HYDROQUINONE

Hydroquinone = 1,4-Benzenediol = HQ = 1,4-Dihydroxybenzene

CAS Number: 123-31-9 
EC Number: 204-617-8
Chemical formula: C6H6O2
Molar mass: 110.112 g·mol−1

Hydroquinone, also known as benzene-1,4-diol or quinol, is an aromatic organic compound that is a type of phenol, a derivative of benzene, having the chemical formula C6H4(OH)2. 
Hydroquinone has two hydroxyl groups bonded to a benzene ring in a para position. 
Hydroquinone is a white granular solid. 
Substituted derivatives of this parent compound are also referred to as hydroquinones. 
The name "hydroquinone" was coined by Friedrich Wöhler in 1843
Hydroquinone is applied to the the skin to lighten areas that have darkened. 
Hydroquinone also contain sunscreens.
Hydroquinone is an organic chemical that is normally produced industrially and has a very similar structure to the precursors of Melanin.
The most common use of Hydroquinone is in skin lightening products, although it can also be used in a technique for developing black and white photos.
Hydroquinone is the most commonly prescribed depigmenting agent worldwide.

Hydroquinone is a topical skin-bleaching agent used in the cosmetic treatment of hyperpigmented skin conditions. 
The effect of skin lightening caused by hydroquinone is reversible when exposed to sunlight and therefore requires regular use until desired results are achieved. 
Various preparations are available including creams, emulsions, gels, lotions and solutions. 
Hydroquinone is available over the counter in a 2% cream and can be prescribed by your dermatologist in higher concentrations.

Mechanism: 
Hydroquinone produces reversible lightening of the skin by interfering with melanin production by the melanocytes. 
Specifically, inhibition of the enzymatic conversion of tyrosine to DOPA (dihydroxyphenylalanine) results in the desired chemical reduction of pigment. 
Ultimately, this causes a decrease in the number of melanocytes and decreased transfer of melanin leading to lighter skin.

Uses: 
Popularized by Hydroquinones usage as a photo-developer, hydroquinone can be used in any condition causing hyperpigmentation. 
Common conditions of Hydroquinone include melasma, freckles, lentigines, age spots and acne scars. 
Skin sensitivity to hydroquinone may be determined before treatment by applying a small amount of cream to the hyperpigmented area and noting any redness or itching. 
If no reaction occurs, initiate treatment. 
As a general rule, always ensure the area is clean and dry then apply a thin film to the lesion and rub it into the skin well. 
Hands should be washed after the application to avoid unwanted lightening of the fingers.

To maintain the desired affect, hydroquinone should be used concurrently with a strong sunscreen. 
Many preparations are available as a combination product. 
Lightening of the skin should be noticed within 4 weeks of initiation, if no change is seen in 3 months, contact your dermatologist for further recommendations.

Hydroquinone is a chemical that a person can use to lighten their skin tone. 
Hydroquinone is available as a cream, gel, lotion, or emulsion. 
Hydroquinone is generally safe to use, but some people may experience side effects, such as dry skin.

Hydroquinone is a chemical that bleaches the skin. 
Hydroquinone can come as a cream, emulsion, gel, or lotion. 
A person can apply Hydroquinone directly to the skin.
Creams that contain 2% hydroquinone are available to buy over the counter in most drugstores. 
Stronger creams are available with a prescription from a doctor.
People may use hydroquinone as a form of treatment for hyperpigmentation skin conditions, wherein some areas of skin grow darker than surrounding areas.
Some conditions that people may use hydroquinone for include:
-Hydroquinone and Melasma
-People with melasma have brown or gray-brown patches on their skin. 
-These patches tend to develop on the face, such as the cheeks or nose. 
-They can also appear on areas of skin with high sun exposure, such as the forearms and neck.

Hydroquinone and Freckles
Freckles are darker spots or patches that usually occur in fair skin. 
Hydroquinone can become more noticeable with exposure to sunlight.

Hydroquinone and Lentigines
Lentigines, or age spots, develop on areas of skin with the highest sun exposure. 
For example, Hydroquinone can appear on the face or the backs of the hands.
They tend to be flat, dark, and between 0.2 centimeters (cm) and 2 cm in width.

Hydroquinone and acne scars
Excess oil, dead skin cells, and bacteria can build up in skin pores and cause acne. 
The body tries to repair the damage, but sometimes, it leaves scars.

Other uses of Hydroquinone:
Some people may want to lighten their skin for cosmetic reasons. 
Hydroquinone can have benefits for confidence and self-esteem.
Hydroquinone is important to note that the above conditions are all harmless.

How does Hydroquinone work?
Melanin is a pigment that gives the skin and hair their color. 
Hydroquinone is responsible for freckles and other dark patches on the skin. 
Melanin is made by melanocytes, which are cells present in the skin and other parts of the body.
When a person applies hydroquinone to the skin, it reduces the number of melanocytes. 
Fewer melanocytes means that the body produces less melanin in the treated area. 
The skin usually appears lighter within about 4 weeks.
Exposure to sunlight reverses the effects of hydroquinone. 
Doctors recommend that people who use this product also use a strong sunscreen.

Hydroquinone is known to inhibit melanogenesis both in vitro and in vivo. 
In this study, 2% and 5% hydroquinone creams were topically applied to the hyperpigmented skin of 56 patients. 
Hydroquinone used in this way, hydroquinone was a moderately effective depigmenting agent in 80% of cases. 
The 2% cream appeared to be as effective therapeutically as the 5% cream and to evoke untoward side effects (primary irritation) much less often. 
Therapy with topically applied hydroquinone did not lead to complete disappearance of pathological hypermelanosis, but results were satisfactory enough to help most patients become less self-conscious about their pigmentary abnormalities.

Hydroquinone production
Hydroquinone is produced industrially by two main routes.
The most widely use of Hydroquinone route is similar to the cumene process in reaction mechanism and involves the dialkylation of benzene with propene to give 1,4-diisopropylbenzene. 
This compound reacts with air to afford the bis(hydroperoxide), which is structurally similar to cumene hydroperoxide and rearranges in acid to give acetone and hydroquinone.
A second route involves hydroxylation of phenol over a catalyst. 

Hydroquinone topical (for the skin) is used to lighten areas of darkened skin such as freckles, age spots, melasma (sun damage), or chloasma (darkened skin caused by hormonal changes).
Hydroquinone topical may also be used for purposes not listed in this medication guide.

The conversion uses hydrogen peroxide and affords a mixture of hydroquinone and catechol (benzene-1,2-diol):
C6H5OH + H2O2 → C6H4(OH)2 + H2O
Other, less common methods include:
A potentially significant synthesis of hydroquinone from acetylene and iron pentacarbonyl has been proposed. 
Iron pentacarbonyl serves as a catalyst, rather than as a reagent, in the presence of free carbon monoxide gas. 
Rhodium or ruthenium can substitute for iron as the catalyst with favorable chemical yields but are not typically used due to their cost of recovery from the reaction mixture.
Hydroquinone and its derivatives can also be prepared by oxidation of various phenols. 
Examples include Elbs persulfate oxidation and Dakin oxidation:
Hydroquinone was first obtained in 1820 by the French chemists Pelletier and Caventou via the dry distillation of quinic acid.

Hydroquinone Reactions
The reactivity of hydroquinone's hydroxyl groups resembles that of other phenols, being weakly acidic. 
The resulting conjugate base undergoes easy O-alkylation to give mono- and diethers. 
Similarly, hydroquinone is highly susceptible to ring substitution by Friedel–Crafts reactions such as alkylation. 
This reaction is exploited en route to popular antioxidants such as 2-tert-butyl-4-methoxyphenol (BHA). 
The useful dye quinizarin is produced by diacylation of hydroquinone with phthalic anhydride.

Redox
Hydroquinone undergoes oxidation under mild conditions to give benzoquinone. 
This process of Hydroquinone can be reversed. 
Some naturally occurring hydroquinone derivatives exhibit this sort of reactivity, one example being coenzyme Q. 
Industrially this reaction is exploited both with hydroquinone itself but more often with its derivatives where one OH has been replaced by an amine.
When colorless hydroquinone and benzoquinone, a bright yellow solid, are cocrystallized in a 1:1 ratio, a dark-green crystalline charge-transfer complex (melting point 171 °C) called quinhydrone (C6H6O2·C6H4O2) is formed. 
Hydroquinone dissolves in hot water, where the two molecules dissociate in solution.

Amination
An important reaction is the conversion of hydroquinone to the mono- and diamine derivatives. 
Methylaminophenol, used in photography, is produced in this way:
C6H4(OH)2 + CH3NH2 → HOC6H4NHCH3 + H2O
Similarly diamines, useful in the rubber industry as antiozone agents, are produced similarly from aniline:
C6H4(OH)2 + 2 C6H5NH2 → C6H4(N(H)C6H5)2 + 2 H2O

Hydroquinone uses
Hydroquinone has a variety of uses principally associated with its action as a reducing agent that is soluble in water. 
Hydroquinone is a major component in most black and white photographic developers for film and paper where, with the compound metol, it reduces silver halides to elemental silver.
There are various other uses associated with its reducing power. 
As a polymerisation inhibitor, exploiting its antioxidant properties, hydroquinone prevents polymerization of acrylic acid, methyl methacrylate, cyanoacrylate, and other monomers that are susceptible to radical-initiated polymerization. 
By acting as a free radical scavenger, hydroquinone serves to prolong the shelflife of light-sensitive resins such as preceramic polymers.
Hydroquinone can lose a hydrogen cation from both hydroxyl groups to form a diphenolate ion. 
The disodium diphenolate salt of hydroquinone is used as an alternating comonomer unit in the production of the polymer PEEK.

Skin depigmentation
Hydroquinone is used as a topical application in skin whitening to reduce the color of skin. 
Hydroquinone does not have the same predisposition to cause dermatitis as metol does. 
This is a prescription-only ingredient in some countries, including the member states of the European Union under Directives 76/768/EEC:1976.
In 2006, the United States Food and Drug Administration revoked Hydroquinones previous approval of hydroquinone and proposed a ban on all over-the-counter preparations.
The FDA stated that hydroquinone cannot be ruled out as a potential carcinogen.
This conclusion was reached based on the extent of absorption in humans and the incidence of neoplasms in rats in several studies where adult rats were found to have increased rates of tumours, including thyroid follicular cell hyperplasias, anisokaryosis (variation in nuclei sizes), mononuclear cell leukemia, hepatocellular adenomas and renal tubule cell adenomas. 
The Campaign for Safe Cosmetics has also highlighted concerns.
Numerous studies have revealed that hydroquinone, if taken orally, can cause exogenous ochronosis, a disfiguring disease in which blue-black pigments are deposited onto the skin; however, skin preparations containing the ingredient are administered topically. 
The FDA had classified hydroquinone in 1982 as a safe product - generally recognized as safe and effective (GRASE), however additional studies under the National Toxicology Program (NTP) were suggested in order to determine whether there is a risk to humans from the use of hydroquinone.
NTP evaluation showed some evidence of long-term carcinogenic and genotoxic effects.

While using hydroquinone as a lightening agent can be effective with proper use, it can also cause skin sensitivity. 
Using Hydroquinone a daily sunscreen with a high PPD (persistent pigment darkening) rating reduces the risk of further damage. 
Hydroquinone is sometimes combined with alpha-hydroxy acids that exfoliate the skin to quicken the lightening process. 
In the United States, topical treatments usually contain up to 2% in hydroquinone. 
Otherwise, higher concentrations (up to 4%) should be prescribed and used with caution.
While hydroquinone remains widely prescribed for treatment of hyperpigmentation, questions raised about its safety profile by regulatory agencies in the EU, Japan, and USA encourage the search for other agents with comparable efficacy.
Several such agents are already available or under research, including azelaic acid, kojic acid, retinoids, cysteamine, topical steroids, glycolic acid, and other substances. 
One of these, 4-butylresorcinol, has been proven to be more effective at treating melanin-related skin disorders by a wide margin, as well as safe enough to be made available over the counter.

What Is Hydroquinone?
Hydroquinone is the common name for the ingredient 1,4-dihydroxybenzene, and may be used safely in a variety of cosmetics.

Why is Hydroquinone used in cosmetics and personal care products?
Hydroquinone is used in cosmetics as an antioxidant, fragrance ingredient and oxidizing agent in hair dyes.  
Hydroquinone may also be used as a stabilizer that inhibits the polymerization of the adhesive in artificial nails.

Natural occurrences
Hydroquinones are one of the two primary reagents in the defensive glands of bombardier beetles, along with hydrogen peroxide (and perhaps other compounds, depending on the species), which collect in a reservoir. 
The reservoir opens through a muscle-controlled valve onto a thick-walled reaction chamber. 
This chamber is lined with cells that secrete catalases and peroxidases. 
When the contents of the reservoir are forced into the reaction chamber, the catalases and peroxidases rapidly break down the hydrogen peroxide and catalyze the oxidation of the hydroquinones into p-quinones. 
These reactions release free oxygen and generate enough heat to bring the mixture to the boiling point and vaporize about a fifth of it, producing a hot spray from the beetle's abdomen.
Farnesyl hydroquinone derivatives are the principal irritants exuded by the poodle-dog bush, which can cause severe contact dermatitis in humans.
Hydroquinone is thought to be the active toxin in Agaricus hondensis mushrooms.
Hydroquinone has been shown to be one of the chemical constituents of the natural product propolis.
Hydroquinone is also one of the chemical compounds found in castoreum. This compound is gathered from the beaver's castor sacs.
In bearberry (Arctostaphylos uva-ursi), arbutin is converted to hydroquinone.

WHAT IS HYDROQUINONE?
Hydroquinone is an organic compound that can be found naturally in different fungi, plants and animals but was first synthetically produced in the 1800s for the purposes of developing black and white photography. 
Later on, in the beginning of the 20th century, the effects of Hydroquinone on the skin as a melanin inhibitor, and antioxidant were discovered and the ingredient was put to use in topical skincare. 
For the last 50+ years, Hydroquinone has been the gold standard for dark spot correcting and recommended by a number of board-certified dermatologists including SLMD founder, Dr. Sandra Lee, for reducing the appearance of pigmentation resulting from acne, melasma, and sun exposure. 
Misinformation and confusion has caused Hydroquinone to become a controversial ingredient, but we’re here to set the record straight and share the right info with you!

IS Hydroquinone DANGEROUS?
The first misconception that Hydroquinone is dangerous stemmed from a controversy in South Africa, in 1980, after they identified products containing Hydroquinone to be hazardous. 
As a result, South Africa placed a ban on the ingredient, and Japan, EU and Australia followed suit. 
However, further research uncovered that these products they identified as hazardous also contained mercury and other illegal contaminants. 
Therefore, there was no substantial evidence that the reason for this toxicity was due to the Hydroquinone, and plenty more research upholds Hydroquinone to be safe and effective when used topically!
A skin disorder known as exogenous ochronosis, which causes skin to darken with blue-black pigmentation, has been linked to the use of prescription strength Hydroquinone chronically (long-term) and at very high percentages. 
Hydroquinone is important to note that this occurrence is very rare — there have been less than 40 cases recorded in the US. 
For this reason, when using prescription strength HQs, dermatologists will recommend that after a couple months of use you take a break from the product before continuing your treatment.
Similarly, there has been no evidence or study that indicates that use of a topical Hydroquinone causes cancer in humans. 
Hydroquinone is true that hydroquinone should not be ingested orally in high doses, but as it's manufactured in its powdered form for topical skincare, it's a very stable, safe ingredient!

HOW DOES HYDROQUINONE WORK?
Hydroquinone works to reduce the appearance of dark spots over time by decreasing the production of melanin (the protein that gives your skin pigment) and increasing the breakdown of melanocytes (the cells that create melanin). 
This works because Hydroquinone prevents the activity of tyrosinase, the enzyme needed to make melanin.
Melanin is a natural function of our skin — it’s how we get the pigment in our skin, eyes, and hair, but it becomes problematic when Melanocytes (which sit in the Dermis layer of our skin) are stimulated to release extra melanin that form dark spots on the top layer of our skin. 
This process can be triggered by UV exposure and trauma (from picking at your skin). 
Hydroquinone also has some antioxidant properties that help protect the skin from UV damage and brighten complexion. 
Because Hydroquinone functions on the cell-level, it requires consistent use to see results  — it is not bleaching your skin over time, just making the melanin production of your skin more even. 

Safety Information: 
CIR Safety Reviews

Hydroquinone’s safety has been assessed by the Cosmetic Ingredient Review (CIR) Expert Panel on four separate occasions since 1986. 
CIR concluded that hydroquinone is safe at concentrations of ≤ 1% in cosmetic formulations designed for discontinuous, brief use followed by rinsing from the skin and hair. 
In addition, hydroquinone is safe for use as a polymerization inhibitor in nail adhesives and in artificial nail coatings that are cured by LED light. 
However, hydroquinone is not safe for use in other leave-on cosmetic products.

European Union (EU)
Hydroquinone is listed in Annex III, entry 14 which allows the use of hydroquinone in artificial nail systems with a maximum concentration of 0.02% (200 ppm) after mixing for use, by professionals only. 
This is the only approved cosmetic use in the EU.

What is hydroquinone?
Hydroquinone is a skin-lightening agent. 
Hydroquinone bleaches the skin, which can be helpful when treating different forms of hyperpigmentation.
Historically, there’s been some back-and-forth on the safety of hydroquinone. 
In 1982, the U.S. Food and Drug Administration recognized the ingredient as safe and effectiveTrusted Source.
Several years later, concerns about safety prompted retailers to pull hydroquinone from the market. 
The FDA went on to discover that many of the products in question contained contaminants like mercury. 
They established that these contaminants were behind reports of adverse effects.
Since then, the FDA has confirmed that hydroquinone can be safely sold over the counter (OTC) in 2 percent concentrations.
Read on to learn more about how it works, who might benefit from use, products to try, and more.

How does Hydroquinone work?
Hydroquinone bleaches your skin by decreasing the number of melanocytes present. 
Melanocytes make melanin, which is what produces your skin tone.
In cases of hyperpigmentation, more melanin is present due to an increase in melanocyte production. 
By controlling these melanocytes, your skin will become more evenly toned over time.
Hydroquinone takes about four weeks on average for the ingredient to take effect. 
Hydroquinone may take several months of consistent use before you see full results.
If you don’t see any improvements within three months of OTC use, talk to your dermatologist. 
They may be able to recommend a prescription-strength formula better suited to your needs.

What is hydroquinone topical?
Hydroquinone decreases the formation of melanin in the skin. 
Melanin is the pigment in skin that gives it a brown color.
Hydroquinone topical is used to lighten areas of darkened skin such as freckles, age spots, Chloasma, and Melasma. 
Hydroquinone works by inhibiting an enzyme reaction in skin cells.

How should I use hydroquinone topical?
Do not use hydroquinone topical on skin that is sunburned, dry, chapped, or irritated, or on an open wound. 
Hydroquinone could make these conditions worse. 
Discontinue use if excessive irritation develops. 
Apply the medication to clean, dry skin.
Dispense a pea size amount on the back of your hand, apply to cheeks, forehead and then to chin. 
Blend in the product to cover face. 
Avoid the corners of the mouth and nose; these areas can be irritated easily. 
Apply to the affected area(s) morning and night. 
For Melasma, once the discoloration has resolved or adequately faded, you may either discontinue use or continue weekly maintenance.
Hydroquinone may take 3 months or more to see improvements. 
For Lentigines, use the creams for a maximum of 3 months.

What skin conditions can benefit from Hydroquinone?
Hydroquinone is used to treat skin conditions related to hyperpigmentation. 
Hydroquinone includes:
-acne scars
-age spots
-freckles
-melasma
-post-inflammatory marks from psoriasis and eczema
Although hydroquinone can help fade red or brown spots that have lingered, Hydroquinone won’t help with active inflammation. 
For example, Hydroquinone can help minimize acne scarring, but Hydroquinone won’t have an effect on redness from active breakouts.

What do I need to tell my doctor BEFORE I take Hydroquinone?
If you have an allergy to hydroquinone or any other part of hydroquinone.
If you are allergic to hydroquinone; any part of hydroquinone; or any other drugs, foods, or substances. 
Tell your doctor about the allergy and what signs you had.
Hydroquinone may interact with other drugs or health problems.

What is hydroquinone?
Hydroquinone is a topical cream that is used to lighten dark patches of the skin (also called hyperpigmentation). 
Hydroquinone is available as a prescription alone and as a combination cream containing a topical steroid and a topical retinoid. 
In some countries, including the United States, Hydroquinone is available over the counter, most often in a 2-3% formulation. 

What is hydroquinone used for?
Hydroquinone is used to lighten dark patches of the skin. 
These dark spots can be related or triggered by many factors including pregnancy, birth control pills, inflammation, and injury to the skin.  
The most common use is for melasma, a condition in which people develop dark patches on the face and other areas of skin, such as the arms.

How is Hydroquinone used?
Safe use of hydroquinone includes using it under the supervision of a dermatologist. 
Hydroquinone should be applied only to the affected darkened areas of skin to avoid lightening of normal skin. 
Hydroquinone should not be used for extended periods of time as it can cause a paradoxical darkening. 
Cycling of use with breaks is recommended to limit overuse and the side effect known as exogenous ochronosis.  

What else do I need to know about hydroquinone?
Hydroquinone is an out of pocket expense as insurance will not cover this medication. 
If using Hydroquinone to treat melasma, Hydroquinone should be used in combination with a broad-spectrum sunscreen SPF 30 or higher daily. 
Sunscreen should be applied to the affected areas after hydroquinone to avoid relapse of the condition. 
Dark areas may recur if the cream is discontinued but this is less likely happen if sun protective measures are followed.

Tell your doctor and pharmacist about all of your drugs (prescription or OTC, natural products, vitamins) and health problems. 
You must check to make sure that it is safe for you to take hydroquinone with all of your drugs and health problems.
Do not start, stop, or change the dose of any drug without checking with your doctor.

Hydroquinone cream is the standard depigmentation or skin lightening agent. 
Clinically Hydroquinone is used to treat areas of dyschromia, such as in melasma, chloasma, solar lentigines, freckles, and post-inflammatory hyperpigmentation. 
This activity outlines the indications, mechanism of action, methods of administration, important adverse effects, contraindications, and monitoring of hydroquinone, so providers can direct patient therapy to optimal outcomes in conditions where it is indicated.

What is Hydroquinone?
Hydroquinone also known as tocopheryl acetate, hydroquinone is found in skin-lightening creams, serums, cleansers, and moisturizers. 
"Hydroquinone is a topical skin treatment for melasma, freckles, age and sun spots, and even acne scars," Shafer says. 
"Hydroquinone is used in combination with other acne products such as Retin-A, hydroquinone can help dramatically improve skin complexion.
"Shamban adds to this, reporting that hydroquinone can also be used to lighten up freckles as well as post-inflammatory hyperpigmentation, which is usually seen after an injury such as a burn or inflammatory acne.

While hydroquinone is effective at lightening spots, the results aren't immediate. 
Hydroquinone may take a matter of weeks (or months) before results are discernible to the naked eye. 
"Patients need to understand that the treatment is working at the cellular level to reduce the production of pigment," Shafer explains. 
"So the effects take several weeks to realize. 
As the old skin sheds and new skin is produced, the amount of pigment will be less, leading to a more even skin tone."

Benefits of Hydroquinone for Skin
Hydroquinone has several benefits for the skin.
Lightens dark spots (hyperpigmentation): Hydroquinone is one of the most effective ingredients to lighten hyperpigmentation. 
"If you have dark areas from melasma, age spots, or brown spots left from acne, hydroquinone helps by decreasing the formation of melanin in the skin (the pigment in the skin that gives it a dark color)," says Buttiglione. 
Ng adds: "To date, hydroquinone is considered the topical gold standard in dermatology for reducing hyperpigmentation."
Evens out skin tone: Because hydroquinone lightens certain areas of the skin that are darkened, the end result is a more balanced, even complexion.

Treats melasma: "Hydroquinone serves as the backbone of any treatment for a wide variety of conditions, including melasma," notes Shamban. 
"Melasma, which is manifested by patches of darker skin typically on the forehead, cheeks, and upper lip, often runs in families and is triggered by UV and visible light exposure often in combination with hormonal shifts such as birth control pills, pregnancy or hormone replacement therapy." 
Hydroquinone can help rectify the side effects of melasma.

How to Use Hydroquinone
"Over the years I have never found a more effective treatment for unwanted pigmentation than glycolic acid and hydroquinone," says Bottiglione. 
"I recommend using hydroquinone after cleansing the skin with a glycolic acid cleanser, like the Dermatologist's Choice pH Balanced Cleanser with Glycolic Acid ," says Bottiglione. 
"The key is to eliminate excess oil, dirt, and makeup that can block the hydroquinone from entering the pores. 
The deeper the hydroquinone can penetrate into the skin, the better the benefits." 
And, while we all know the harmful effects of the sun on our skin, Hydroquinone can cause further darkening of spots, so using a UV-blocking sunscreen during the time you're using any hydroquinone product is a must.
"Most people don't need it all over the skin, just in particular areas," Bottiglione advises. 
"You should use Hydroquinone in the areas with hyperpigmentation." 

If you tend to be sensitive, Bottiglione recommends using Hydroquinone on alternating days, which can help the skin tolerate Hydroquinone better. 
"Using an over-the-counter option at a low concentration can help the skin tolerate it better as well," he notes.
Over-the-counter hydroquinone products are available at concentrations up to 2%. 
Anything higher than that requires a prescription. 
"I usually recommend evening before bedtime as I like to use the cellular regenerative hours overnight for the product to get to work," says Shamban. 
Also, Ng notes that hydroquinone makes skin more susceptible to UV damage and that insufficient sun protection during treatment can lead to the development of more hyperpigmentation—always ensure your skin is protected while donning a hydroquinone treatment.

What do I do if I miss a dose?
-Put on a missed dose as soon as you think about Hydroquinone.
-If Hydroquinone is close to the time for your next dose, skip the missed dose and go back to your normal time.
-Do not put Hydroquinone on 2 doses or extra doses.

Preferred IUPAC name:
Benzene-1,4-diol

What is Hydroquinone?
HYDROQUINONE (hahy droh kwi NOHN) is applied to the the skin to lighten areas that have darkened. 
Some products also contain sunscreens.
Hydroquinone may be used for other purposes; ask your health care provider or pharmacist if you have questions.

COMMON BRAND NAME(S): Aclaro, Aclaro PD, Alera, Alphaquin HP, Alustra, Claripel, Complex B, Dermarest Skin Correcting Cream Plus, Eldopaque Forte, Eldoquin Forte, EpiQuin Micro, Esoterica, Glyquin, Glyquin XM, Lustra, Lustra-AF, Lustra-Ultra, Melanex, Melpaque HP, Melquin HP, Melquin-3, Nava-SC, Nuquin HP, Skin Bleaching, Solaquin Forte

What should I tell my health care provider before I take Hydroquinone?
They need to know if you have any of these conditions:
-an unusual or allergic reaction to hydroquinone, sunscreens, other medicines, foods, dyes, or preservatives
-pregnant or trying to get pregnant
-breast-feeding

How should I use Hydroquinone?
Hydroquinone is for external use only. 
Do not take Hydroquinone by mouth. 
Follow the directions on the prescription label. 
Wash your hands before and after applying Hydroquinone. 
Make sure the skin is clean and dry. 
Apply Hydroquinone just enough to cover the affected area. 
Rub in gently but completely. 
Do not apply Hydroquinone near the eyes, mouth, or other areas of sensitive skin. 
If accidental contact occurs, large amounts of water should be used to wash the affected area. 
If the eyes are involved and eye irritation persists after thoroughly washing, contact your doctor. 
If you are using other skin medicines, apply them at different times of the day. 
Do not use Hydroquinone more often than directed.
Talk to your pediatrician regarding the use of Hydroquinone in children. 
Special care may be needed.

Overdosage: If you think you have taken too much of Hydroquinone contact a poison control center or emergency room at once.

NOTE: 
Hydroquinone is only for you.
Do not share Hydroquinone with others.

What if I miss a Hydroquinone dose?
If you miss a dose, apply Hydroquinone as soon as you can. 
If Hydroquinone is almost time for your next dose, use only that dose. 
Do not use Hydroquinone double or extra doses.

What may interact with Hydroquinone?
benzoyl peroxide
This list may not describe all possible interactions. 
Give your health care provider a list of all the medicines, herbs, non-prescription drugs, or dietary supplements you use. 
Also tell them if you smoke, drink alcohol, or use illegal drugs. 
Some items may interact with Hydroquinone.

Hydroquinone, the major benzene metabolite, is a ubiquitous chemical in the environment due to its widespread application in human and industrial activities. 
Hydroquinone can be used as a developing agent in photography, dye intermediate, stabilizer in paints, varnishes oils, and motor fuels. 
In addition, hydroquinone has been used as an antioxidant in the rubber and food industry. 
From 1950s to 2001 hydroquinone was applied in the commercially available cosmetic skin lightening formulations in European Union countries and since 1960s it was commercially available as a medical product. 
Hydroquinone is also present in cosmetic formulations of products for coating finger nails and hair dyes. 
On the other hand, hydroquinone can be a component of high molecular aromatic compounds (e.g., resin), an intermediate, or appear as a degradation product generated by transformation of aromatic compounds. 
Advanced oxidation processes (APOs) of aromatic compounds, particularly of phenol, yield several benzene derivatives, such as hydroquinone, catechol, and resorcinol, as intermediate metabolites of its transformation. 
The formation of hydroquinone and -benzoquinone at early stages of phenol oxidation increases the toxicity of phenol wastewaters, showing that these compounds were more toxic and less degradable than the original pollutant. 
Meanwhile, in the oxidative degradation of hydroquinone under a supercritical condition (409.9°C and 24.5 MPa) and subcritical condition (359.9°C and 24.5 MPa), -benzoquinone was to be an important intermediate. 
Despite the toxic properties, a number of microorganisms can utilize hydroquinone, especially under aerobic conditions, which has led to the development of low-cost treatment of polluted effluents. 
The chemical method applied conventionally to the treatment of industrial wastewater used FeSO4 and H2O2; however, the application of this technology generates ferric sulfate, which enables recycled reactants. 
Therefore, biological transformations are generally preferred for being considered as more economical and environmentally friendly.

What should I watch for while using Hydroquinone?
Contact your doctor or health care professional if your condition does not improve in the first two months or if you experience too much skin irritation.
Hydroquinone will work best if you avoid excessive exposure to sunlight and wear sunscreens and protective clothing. 
Some hydroquinone products contain sunscreens. 
Use a sunscreen (SPF 15 or higher). 
Do not use sun lamps or sun tanning beds or booths. 
Do not apply Hydroquinone to sunburned areas or if you have a skin wound in the area of application.
Most cosmetics, sunscreens, and moisturizing lotions may be worn over Hydroquinone. 
Wait several minutes after application of v before applying them.

What side effects may I notice from receiving Hydroquinone?
Side effects that you should report to your doctor or health care professional as soon as possible:
-severe burning, itching, crusting, or swelling of the treated areas
-unusual skin discoloration

Side effects that usually do not require medical attention (report to your doctor or health care professional if they continue or are bothersome):
-mild itching or stinging
-reddening of the skin
This list may not describe all possible side effects. 
Call your doctor for medical advice about side effects. 
You may report side effects to FDA at 1-800-FDA-1088.

Hydroquinone is one of the most effective skin brightening agents in skincare. 
However, Hydroquinone’s scientifically proven to have negative side effects. 
Are the Hydroquinone dangers worth risking your health?
Snow White set the bar high when Hydroquinone comes to fair skin.
Many women want overall brighter complexions, and they’re enlisting the help of cosmetics marketed towards brightening dull skin and lightening dark spots.
Skin brightening is so popular and in demand that Hydroquinone’s become its own industry with Asian countries accounting for more than half of sales.

What is Hydroquinone?
Hydroquinone is a skin lightening agent frequently used in skin brightening spot treatments and face creams. 
Hydroquinone’s been long established as the most effective ingredient for lightening skin, fading uneven skin tone, and improving dark spots.
How does hydroquinone work? Hydroquinone bleaches the skin and, therefore, alters the skin tone.
Your skin tone is determined by the amount of melanocytes present in the skin. 
Melanocytes are skin cells that create melanin, a dark brown or black pigment. 
Melanin is also responsible for making skin appear tanned or darker when exposed to sunlight. 
Melanin is beautiful, but Hydroquinone disagrees.
If bleaching your skin doesn’t sound safe to you, you’re right. 
Hydroquinone’s not safe or healthy. 
Yes, Hydroquinone works for its desired purposes, but Hydroquinone’s not good for your skin or body.
Despite its popularity and effectiveness, hydroquinone use is controversial for health and safety reasons.

Where should I keep my medicine?
Keep out of the reach of children.
Store at room temperature between 15 and 30 degrees C (59 and 86 degrees F). 
Do not freeze. 
Throw away any unused medicine after the expiration date.

NOTE: This sheet is a summary. 
Hydroquinone may not cover all possible information. 
If you have questions about this medicine, talk to your doctor, pharmacist, or health care provider.

How to use Hydroquinone
A person should check to see if they are at risk of side effects before they start to use a hydroquinone cream, gel, or lotion regularly. 
HydroquinoneThey can do this by applying a small amount of the product to the affected area of skin.
Check for signs of irritation, such as itching or redness. 
If there is no reaction, Hydroquinone is usually safe to start treatment.
First, make sure that the area is clean and dry. 
Apply Hydroquinone a thin layer of product to the affected skin and rub it in well. 
Lastly, wash the hands thoroughly. 
This will stop the hydroquinone from lightening the skin on the fingers.
Repeat this process as often as the product label advises. 
Hydroquinone is important to protect the affected areas of skin from sunlight. 
Hydroquinone will stop the sun from reversing the effects of the cream.
According to the AOCD, people should start to notice that they have lighter skin within about 4 weeks of using the product. 
If there are no changes after 3 months, a person can speak to a doctor or skin specialist.

Other names:
Hydroquinone
Idrochinone
Quinol
1,4-Dihydroxybenzene
1,4-Hydroxy benzene

Hydroquinone is the LeBron James of skin care. 
The skin lightener is as controversial as Hydroquinone is effective. 
When incorporated into your complexion regimen properly, hydroquinone decreases the production of melanin by inhibiting tyrosinase, an enzyme needed for melanin production, to decrease the appearance of hyperpigmentation. 
Because of this, many people consider Hydroquinone to be a skin-bleaching ingredient.
According to Miami-based board-certified dermatologist Roberta Del Campo, it should be considered a "color blender" instead. 

What are some things I need to know or do while I take Hydroquinone?
-Tell all of your health care providers that you take hydroquinone. 
-This includes your doctors, nurses, pharmacists, and dentists.
-After stopping hydroquinone, some of the color change may come back.
-If you have a sulfite allergy, talk with your doctor.
-This medicine may cause harm if swallowed. 
-If hydroquinone is swallowed, call a doctor or poison control center right away.
-Avoid sun, sunlamps, and tanning beds. 
-Use sunscreen and wear clothing and eyewear that protects you from the sun.
-Tell your doctor if you are pregnant or plan on getting pregnant. 
-You will need to talk about the benefits and risks of using hydroquinone while you are pregnant.
-Tell your doctor if you are breast-feeding. 
-You will need to talk about any risks to your baby.

Boiling Point: 285.0°C to 287.0°C
Flash Point: 165°C
Packaging: Glass Bottle
Sulfated Ash: 0.05% max.
Quantity: 5g
Melting Point: 170.0°C to 174.0°C
Color: White
Density: 1.32
Infrared Spectrum: Authentic
Assay Percent Range: 99.4% min. (HPLC)
Linear Formula: C6H4(OH)2
Beilstein: 06,836
Fieser: 05,341; 14,249
Merck Index: 15,4845
Solubility Information: 
Solubility in water: 70g/L in water (20°C). 
Other solubilities: soluble in alcohol and ether,slightly soluble in benzene,readily soluble in ethanol,acetone and methanol
Formula Weight: 110.11
Physical Form: Needle-Like Crystals or Crystalline Powder
Percent Purity: 99.5%
Chemical Name or Material: Hydroquinone, p.a.

How is Hydroquinone best taken?
-Use hydroquinone as ordered by your doctor. 
-Do not take hydroquinone by mouth. 
-Use Hydroquinone on your skin only. 
-Keep out of your mouth, nose, and eyes (may burn).
-Wash your hands before and after using Hydroquinone. 
-Do not wash your hands after use Hydroquinone if putting this on your hand.
-Clean affected part before use. 
-Make sure to dry well.
-Put Hydroquinone a thin layer on the affected skin and rub in gently.
-Practice good skin care and avoid the sun.
-Do not use Hydroquinone coverings (bandages, dressings, make-up) unless told to do so by the doctor.
-Do not use Hydroquinone on irritated skin.

Is Hydroquinone safe for all skin types and tones?
Although hydroquinone is generally well-tolerated, there are a few exceptions.
If you have dry or sensitive skin, you may find that hydroquinone causes further dryness or irritation. 
Hydroquinone usually tapers off as your skin adjusts to the ingredient.
People who have normal or oily skin are less likely to experience these side effects.
Hydroquinone tends to work best on fair skin tones. 
If you have a medium-to-dark skin tone, talk with your dermatologist before use. 
Hydroquinone may actually worsen hyperpigmentation in darker skin tones.

How effective is hydroquinone?
In most cases, lightening of skin should be seen after four weeks of treatment. 
Sometimes Hydroquinone may take longer to see any change, but if no bleaching effect is seen after three months of treatment, you should stop using hydroquinone.
To increase the effectiveness of hydroquinone, you should stay out of the sun, or wear protective clothing and use an SPF15+ sunscreen when outdoors. 
Do not use sunlamps or tanning salons.
Hydroquinone is important to use hydroquinone regularly as directed until you achieve the desired bleaching, after which use as needed to maintain results.

Hydroquinone;
p-Benzenediol;
1,4-Benzenediol;
1,4-Dihydroxybenzene;
Benzene-1,4-diol;
Quinol;
4-Hydroxyphenol

How to use hydroquinone
Consistency is key to treating hyperpigmentation. 
You’ll want to use Hydroquinone every day for maximum results. 
Follow all product instructions carefully.
Hydroquinone’s important to do a patch test before your first full application. 
This will allow you to determine how your skin will react and whether it results in unwelcome side effects.
Hydroquinone is a white, odorless, crystalline solid with an extremely low vapor pressure. 
Hydroquinone is moderately soluble in water and highly soluble in alcohol. 
Hydroquinone occurs in the environment as a result of anthropogenic processes, as well as in natural products from plants and animals. 
In the soil, hydroquinone is expected to biodegrade under aerobic conditions. 
Hydroquinone may be removed from the soil by oxidation processes or by direct photolysis on the surface. 

What is the most important information I should know about hydroquinone topical?
Follow all directions on your medicine label and package. 
Tell each of your healthcare providers about all your medical conditions, allergies, and all medicines you use.

What is hydroquinone topical?
Hydroquinone topical (for the skin) is used to lighten areas of darkened skin such as freckles, age spots, melasma (sun damage), or chloasma (darkened skin caused by hormonal changes).

Hydroquinone topical may also be used for purposes not listed in this medication guide.

What should I discuss with my healthcare provider before using hydroquinone topical?
You should not use this medicine if you are allergic to hydroquinone or peroxide.

Ask a doctor or pharmacist if Hydroquinone is safe to use if you have ever had:
-liver or kidney disease;
-asthma or sulfite allergy; or if you are using any antibiotic medicine.
Ask a doctor before using this medicine if you are pregnant or breastfeeding.
Do not give this medicine to anyone under 12 years old without medical advice.

How should I use hydroquinone topical?
Use Hydroquinone exactly as directed on the label, or as prescribed by your doctor.
Hydroquinone topical is usually applied each morning and at bedtime. 
Follow your doctor's dosing instructions very carefully.
Do not take Hydroquinone by mouth. 
Topical medicine is for use only on the skin.
Before you start using hydroquinone topical, use a "test dose" to see if you have an allergic reaction to Hydroquinone. 
Apply Hydroquinone very small amount of the medicine to a small area of healthy skin, and check the area within 24 hours. 
If there is no reaction other than minor redness, begin using the full prescribed amount of Hydroquinone.
Wash your hands before and after applying Hydroquinone, unless you are using Hydroquinone to treat the skin on your hands.
Apply Hydroquinone only to the affected skin areas that need to be lightened. 
Try not to get any medicine on the skin around these areas applyed Hydroquinone.
Do not use hydroquinone topical on open wounds or on sunburned, windburned, dry, chapped, or irritated skin.
Call your doctor if your symptoms do not improve after 2 months, or if your condition gets worse.
Store Hydroquinone at room temperature away from moisture and heat. 
Keep the Hydroquinone container tightly closed when not in use.

What happens if I miss Hydroquinone dose?
Apply Hydroquinone as soon as you can, but skip the missed dose if Hydroquinone is almost time for your next dose. 
Do not apply two doses at one time.

What happens if I overdose?
An overdose of hydroquinone topical is not expected to be dangerous. 

What should I avoid while using hydroquinone topical?
Avoid getting Hydroquinone in your eyes.
Avoid getting Hydroquinone on your lips or inside your nose or mouth. 
Hydroquinone may cause numbness in these areas.
Avoid exposure to sunlight or tanning beds. Hydroquinone topical can make you sunburn more easily. 
Wear protective clothing and use sunscreen (SPF 30 or higher) when you are outdoors. 
Some hydroquinone products may contain sunscreen. Check the medicine label or ask your doctor to be sure.
Hydroquinone topical may make your skin more sensitive to weather extremes such as cold and wind. 
Protect your skin with clothing and use a moisturizing lotion as needed.
Using hydroquinone topical together with benzoyl peroxide, hydrogen peroxide, or other peroxide products may stain your skin. 
This staining can usually be removed with soap and water.
Avoid using skin products that can cause irritation, such as harsh soaps, shampoos, or skin cleansers, hair coloring or permanent chemicals, hair removers or waxes, or skin products with alcohol, spices, astringents, or lime.

What are the possible side effects of hydroquinone topical?
Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Stop using hydroquinone topical and call your doctor at once if you have:
-severe skin redness, burning, or stinging;
-severe skin dryness, cracking, or bleeding;
-blisters or oozing; or
-blue or black discoloration of the skin (especially if you are Hispanic or African-American).

Common side effects may Hydroquinone include:
-mild burning or stinging of treated skin; or
-mild itching, redness, or other irritation.
This is not a complete list of side effects and others may occur. 
Call your doctor for medical advice about side effects. 
You may report side effects to FDA at 1-800-FDA-1088.

What other drugs will affect hydroquinone topical?
Medicine used on the skin is not likely to be affected by other drugs you use. 
But many drugs can interact with each other. 
Tell each of your healthcare providers about all medicines you use, including prescription and over-the-counter medicines, vitamins, and herbal products.

Where can I get more information?
Your pharmacist can provide more information about hydroquinone topical.

Volatilization would be minimal. 
In the water, Hydroquinone would degrade under either aerobic or anaerobic conditions. 
Hydroquinone can also slowly oxidize to quinone, which is more volatile. 
In the air, hydroquinone undergoes photochemical degradation. 
Hydroquinone is listed as undergoing rapid biodegradation in a commercial activated sludge unit under aerobic conditions. 
The estimated and experimental bioconcentration factors for hydroquinone of 40–65 have been obtained. 
These data indicate that hydroquinone is not expected to significantly bioconcentrate in fish and aquatic organisms. 
Hydroquinone, also, does not persist in the environment.

CAS Number: 123-31-9 
Beilstein Reference: 605970
CHEBI: 17594 
ChEMBL: ChEMBL537 
ChemSpider: 764 
ECHA InfoCard: 100.004.199 
EC Number: 204-617-8
Gmelin Reference: 2742
KEGG: D00073
PubChem CID: 785
RTECS number: MX3500000
UNII: XV74C1N1AE check
UN number: 3077, 2662
CompTox Dashboard (EPA): DTXSID7020716

Hydroquinone is a skin lightening agent available as either a pharmaceutical or a cosmeceutical. 
Hydroquinones mechanism of action depends on its ability to inhibit tyrosinase synthesis, thereby inhibiting the production of melanin. 
Other functions of hydroquinone include its ability to inhibit DNA and RNA synthesis, and to degrade melanosomes. 
Products sold at 2% concentration are available in more than 100 over-the-counter products, whereas those with a 3–10% concentration are prescription products and regulated as drugs. 
New products on the market today use hydroquinone in combination with topical retinoids and topical steroids for treatment of melasma and photopigmentation.
Hydroquinone has received scrutiny recently owing to Hydroquinones risk of ochronosis, a severe but rare side-effect. 
Endogenous ochronosis is a manifestation of a rare metabolic disorder known as alkaptonuria, which results from a deficiency of homogentisic acid oxidase. 
Exogenous ochronosis is a rare cutaneous side-effect of the long-term use of topical depigmenting agents such as hydroquinone. 
Ochronosis is characterized by an asymptomatic blue–black pigmentation of skin and cartilage. 
Although the exact cause of ochronosis from topical hydroquinone is not known, studies suggest that hydroquinone may inhibit homogentisic acid oxidase in the dermis, with the accumulation of homogentisic acid in the dermis causing ochronotic pigment deposition. 
Other agents reported in the literature to cause exogenous ochronosis are antimalarials, resorcinol, phenol, mercury, and picric acid.

Hydroquinone is used as an inhibitor of polymerization. 
Due to Hydroquinones outstanding photo developing properties, Hydroquinone is also used as a photo developer, and as a raw material in manufacturing dye intermediates.

To do this:
Rub a small amount of the product into the inside of your forearm.
Cover the area with a bandage.
Wash your hands to prevent the product from staining your clothes or other materials.
Wait 24 hours.
Discontinue use if you experience severe itching or other irritation during this time.
If you don’t experience any side effects, you should be able to safely add it to your skin care routine. 
You should apply Hydroquinone after cleansing and toning, but before your moisturizer.

Hydroquinone is used to lighten the dark patches of skin (also called hyperpigmentation, melasma, "liver spots," "age spots," freckles) caused by pregnancy, birth control pills, hormone medicine, or injury to the skin.
Hydroquinone works by blocking the process in the skin that leads to discoloration.

If OVERDOSE is suspected:
If you think there has been an overdose, call your poison control center or get medical care right away. 
Be ready to tell or show what was taken, how much, and when it happened.

How do I store and/or throw out Hydroquinone?
Store Hydroquinone at room temperature.
Store Hydroquinone in a dry place. 
Do not store Hydroquinone in a bathroom.
Keep Hydroquinone in a safe place. 
Keep Hydroquinone out of the reach of children and pets.
Throw away unused or expired drugs. 
Do not flush Hydroquinone down a toilet or pour down a drain unless you are told to do so. 
Check with your pharmacist if you have questions about the best way to throw out drugs. 
There may be drug take-back programs in your area.

Consumer information use
If your symptoms or health problems do not get better or if they become worse, call your doctor.
Do not share your drugs with others and do not take anyone else's drugs.
Some drugs may have another patient information leaflet. 
Check Hydroquinone with your pharmacist. 
If you have any questions about hydroquinone, please talk with your doctor, nurse, pharmacist, or other health care provider.
If you think there has been an overdose, call your poison control center or get medical care right away. 
Be ready to tell or show what was taken, how much, and when it happened.

Hydroquinone, a bleaching agent, is most frequently used to treat melasma. 
A 2% concentration is available over the counter, whereas 4% hydroquinone cream requires a prescription. 
Hydroquinone is applied twice daily to affected areas. 
Sunscreens with a SPF of 30 should be used prophylactically. 
If after several months no lightening has occurred, tretinoin cream 0.1% may be cautiously applied daily in addition to the use of hydroquinone and a sunscreen. 
In addition, a combination product containing fluocinolone, hydroquinone, and tretinoin (Tri-Luma) is effective. 
Less commonly used treatments include azelaic acid cream (Azelex) and chemical peels.

How to use Hydroquinone Skin Bleaching Cream
Follow all directions on the product package, or use as directed by your doctor. 
Before using, apply a small amount of Hydroquinone to an area of unbroken skin, and check the area within 24 hours for any serious side effects. 
If the test area is itching, red, puffy, or blistering, do not use Hydroquinone and contact your doctor. 
If there is just mild redness, then treatment with Hydroquinone may begin.
Apply Hydroquinone to the affected areas of skin, usually twice daily or as directed by your doctor. 
Hydroquinone is for use on the skin only. 
If Hydroquinone is used incorrectly, unwanted skin lightening may occur. 
Avoid getting Hydroquinone in your eyes or on the inside of your nose or mouth. 
If you do get Hydroquinone in those areas, flush with plenty of water.
Hydroquinone may make the treated areas of skin more sensitive to the sun. 
Avoid prolonged sun exposure, tanning booths, and sunlamps. 
Use Hydroquinone a sunscreen and wear protective clothing on the treated areas of skin when outdoors.
Use Hydroquinone regularly to get the most benefit from it. 
To help you remember, use Hydroquinone at the same times each day.

Hydroquinone is a depigmenting agent used to lighten areas of darkened skin such as freckles, age spots, chloasma, and melisma caused by pregnancy, birth control pills, hormone medicine, or injury to the skin. 
Hydroquinone decreases the formation of melanin in the skin. 
Melanin is the pigment in skin that gives it a brown color.

Chemical formula: C6H6O2
Molar mass: 110.112 g·mol−1
Appearance: white solid
Density: 1.3 g cm−3, solid
Melting point: 172 °C (342 °F; 445 K)
Boiling point: 287 °C (549 °F; 560 K)
Solubility in water: 5.9 g/100 mL (15 °C)
Vapor pressure: 10−5 mmHg (20 °C)[2]
Acidity (pKa): 9.9[3]
Magnetic susceptibility (χ): −64.63×10−6 cm3/mol

Hydroquinone has been used for over 40 years to treat several disorders of hyperpigmentation.
Hydroquinone is the most commonly studied agent for lightening pigment. 
Hydroquinone inhibits the activity of tyrosinase, the enzyme necessary for melanin biosynthesis. 
There are many formulations in the market that combine hydroquinone with alpha hydroxy acids (AHAs), retinol, vitamin C, and topical steroids.
The authors instruct patients to apply a 4% hydroquinone topical cream to the entire face twice daily. 
Patients are cautioned against “spot treatment” to avoid developing a blotchy complexion. 
Patients should be reassured that contrary to popular opinion, hydroquinone does not bleach the skin but rather restores the skin to the patient's baseline skin color.
The evening application should be applied prior to the patient's evening topical retinoid. 
Pretreatment with hydroquinone before skin resurfacing plays an important role in minimizing post-inflammatory hyperpigmentation (PIH).

Take just a small amount of the product and apply it evenly across the entire area of skin. 
Gently massage into your skin until it’s completely absorbed.
Make sure you wash your hands after use — this will prevent the product from affecting other areas of skin or staining your clothes and other materials.
You should also wear sunscreen while using this ingredient. 
Sun exposure can not only make hyperpigmentation worse, but also reverse the effects of your hydroquinone treatment.
Sunscreen is usually the last step of a skin care routine. Be sure to reapply as needed throughout the day.
While consistency is important for maximum results, you shouldn’t use it for long periods of time. 
If you don’t see any improvement after three months, discontinue use.
If you do see improvement, you can use the product for up to four months, and then begin to taper off use. 
You shouldn’t use Hydroquinone for more than five months at a time.
If you want to begin using the product again, wait two to three months before you resume use.

Normally hydroquinone is very well tolerated, however side effects may be seen. 
These include dryness, irritation, pruritus, erythema, and a mild irritant contact dermatitis. 
Furthermore, remember to avoid contact with eyes and use sparingly on the face. 
Prolonged usage of hydroquinone has been associated with ochronosis, a blue-black pigmentation with caviar-like papules on the skin.

Hydroquinone is available under the following different brand names: Lustra, Melquin, Melquin HP 4%, Melquin-3 Topical Solution, Lustra-AF, Lustra-Ultra, Alphaquin, Claripel, Clarite, Eldopaque, Eldoquin, Epiquin Micro, Esoterica, Melanex, Melpaque, Nuquin HP Cream, Nuquin HP Gel, and Solaquin.

What is Hydroquinone?
Hydroquinone is an organic compound that’s used to treat a variety of discoloration-related skin conditions. 
Hydroquinone’s a skin lightening agent that works by reducing your production of melanin. When used topically, hydroquinone can cause your skin to lighten in color.
Hydroquinone is widely used as a scar treatment. 
Applied topically, Hydroquinone can cause darkened scars to lose some or all of their extra pigmentation, causing them to blend in and match the color of the surrounding skin.
Hydroquinone’s also used as a treatment for skin hyperpigmentation caused by UV exposure (spending too much time in the sun) and inflammation.
Topical hydroquinone creams are available as prescription medication to treat melasma and other pigmentation-related skin conditions. 
You can also buy limited strength hydroquinone as an over-the-counter medicine in most pharmacies.

What is Hydroquinone used for?
Hydroquinone is a skin-bleaching agent that is used to lighten areas of darkened skin. 
Hydroquinone decreases the formation of melanin in the skin. 
Melanin is the pigment in skin that gives it a brown color.
Hydroquinone has been prescribed for your present skin condition only and should not be given to other people or used for other problems.

How should I use this medicine?
Wash the skin with cleanser, then rinse and pat dry.
Apply enough Hydroquinone to cover the affected areas, and rub in gently to ensure good absorption.
Apply Hydroquinone once or twice daily, as instructed by your doctor.
You may use a moisturizer to help avoid skin dryness. 
When using moisturizers, sunscreens, cosmetics and other topical preparations together with the hydroquinone cream, apply them in the sequence as instructed by your doctor. 
Wait approximately 3 – 4 minutes before applying the next product.
Do not use the medicine on skin that is sunburned, chapped, or irritated, or on an open wound. 
Hydroquinone could make these conditions worse. 
Wait until these conditions have healed before applying the medicine.
Do not use Hydroquinone in or around the eyes, lips or mouth. 
Hydroquinone may irritate these sensitive areas.

What should I do if I forget a dose?
Skip the missed dose. 
Do not apply more of Hydroquinone to make up for the missed dose as it could result in severe irritation.

What possible side effects may Hydroquinone cause?
Certain side effects of this medicine are not unusual and may even disappear during treatment. 
If any of the following effects on the sites of application persist or are severe, consult your doctor:
-itching
-dryness
-peeling
-mild burning
-redness
-stinging

Stop using Hydroquinone and consult your doctor if the following occurs:
-acne
-blistering
-crusting
-oozing
-scaling
-severe burning
-severe dryness
-severe irritation or itching
-stretch marks
-swelling
-tiny red lines or blood vessels showing through the skin (telangiectasia)

Hydroquinone and unusual skin discoloration
Prolonged use of hydroquinone has been associated with the development of exogenous ochronosis (a persistent blue-black pigmentation). 
Therefore, please use as instructed by your doctor and stop after you have achieved the desired lightening effect.
A very serious allergic reaction to this drug is rare. 
However, seek immediate medical attention if you notice any symptoms of a serious allergic reaction, including: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.
The medication may contain sodium bisulfite, a sulfite that may cause allergic-type reactions including life-threatening or less severe asthmatic episodes in certain susceptible people.

What precautions should I take?
Inform your doctor if you have asthma, other skin conditions (e.g., eczema, psoriasis) or, any unusual or allergic reactions to any topical preparations.

For women: Tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding

Hydroquinone may make the treated areas of skin more sensitive to the sun. 
Avoid prolonged exposure to sunlight, sunlamps or ultraviolet light. 
Use a sunscreen of at least SPF 30 or greater and wear protective covering (e.g. hats, clothing) over the treated areas.

How do I store Hydroquinone?
Keep this medicine away from heat and direct sunlight in a cool, dry place, out of reach of children.

Does Hydroquinone Work for Melasma?
Hydroquinone is one of the most effective topical treatments on the market for melasma. 
Hydroquinone has been thoroughly tested in numerous studies, almost all of which show that it works effectively to reduce pigmentation and even out the blotchy, darkened patches of skin that melasma causes.
In one 2007 study, application of a cream containing hydroquinone and retinol as part of a combination therapy led to “sustained improvements” in skin coloration in people with melasma.
Hydroquinone also performed well in a 2013 study, producing a measurable reduction in MASI scoring (Melasma Area and Severity Index, a scoring system used to assess melasma) over a period of 12 weeks.
In the same study, hydroquinone also produced better results than kojic acid cream—a popular over-the-counter treatment for melasma and skin hyperpigmentation.
In short, hydroquinone is scientifically proven to reduce the amount of skin discoloration caused by melasma. 
For most people, Hydroquinone produces a noticeable improvement after eight to 12 weeks of consistent use, although some people might see improvements in their skin sooner. 
If there is no improvement after two months to three months, you should discontinue and follow up with your healthcare provider. 
However, this doesn’t mean that hydroquinone is guaranteed to treat melasma completely on its own. 
For more severe cases of melasma, hydroquinone is often combined with a topical retinoid such as tretinoin.
For persistent melasma, Hydroquinone’s often used in combination with a retinoid and a corticosteroid. 
This obviously increases the risk of side effects occurring, as many corticosteroids can produce side effects when used over the long term.

How to Use Hydroquinone to Get Rid of Melasma
If you’ve been prescribed hydroquinone, the best approach is to follow the instructions provided by your healthcare provider.
Applying hydroquinone is simple. 
Hydroquinone’s best to test yourself for sensitivity before you begin using hydroquinone regularly. 
To test your skin, apply a small amount of hydroquinone cream to your melasma-affected skin, then check for itchiness or redness over the next 24 hours.

If you don’t experience any itching, soreness or redness, you can start treatment by following the instructions below:
Before applying hydroquinone, clean the hyperpigmented skin.
Make sure the skin is completely dry before applying any hydroquinone cream.
Apply a small amount of hydroquinone cream to the melasma-affected skin. 
Hydroquinone’s best to use just enough cream to cover the hyperpigmented area. 
Take care not to apply any hydroquinone cream to non-melasma skin, as it can potentially lighten its color.
Wash your hands thoroughly after applying the hydroquinone cream. 
Wait for the cream to fully dry before applying makeup, moisturizer, sunscreen or any other topical products.
Take care when applying hydroquinone cream near the eyes, nostrils and mouth. 
If your melasma-affected skin is close to these areas, consider using a cotton swab to apply the cream more precisely.
Avoid using other lightening products on skin you’re treating with hydroquinone, as it’s possible for combinations of lightening agents to cause redness and irritation. 
If you’ve applied too much hydroquinone, wash the excess away using soap and water.

Do not use hydroquinone if you are pregnant or breastfeeding. 
Right now, there simply isn’t enough scientific evidence to show that hydroquinone is completely safe to use in pregnancy — it currently carries a Category C rating from the Food and Drug Administration (FDA).
On average, Hydroquinone takes four to eight weeks for hydroquinone to produce noticeable skin lightening results, meaning you’ll need to apply it consistently before your melasma-affected skin begins to lighten and match the rest of your face.

Is Hydroquinone Safe?
Hydroquinone has been in use for decades, with a good safety record and relatively few safety issues. 
However, like most other skin medications, excessive or improper use of hydroquinone can and often does cause side effects.
The most common side effects of hydroquinone are itchiness, redness, stinging and other forms of skin irritation. 
These are typically mild and temporary. 
Some hydroquinone users notice mild, non-permanent irritation after applying the cream to their skin for the first time.
If you’re sensitive to hydroquinone, it’s also possible for the medication to cause a more severe form of allergic contact dermatitis, which could potentially involve more significant skin burning, itching and crusting. 
In some cases, hydroquinone can cause minor swelling.
If you experience these side effects, it’s best to seek medical advice and cease further use of hydroquinone cream.
Finally, hydroquinone use is linked to the development of ochronosis. 
Hydroquinone is extremely rare, with most cases occurring in Africa. 
Current research indicates that this might be caused by exposure to hydroquinone in combination with antimalarials and other substances.
In general, hydroquinone is a safe, effective medication that’s been successfully used to treat melasma and other skin conditions for decades.

Hydroquinone has been one of the top ingredients physicians use to treat hyperpigmentation. 
There is a lot of controversy on whether to use hydroquinone or go hydroquinone-free. 
With ¼ of all skin care product sales being for hyperpigmentation, this is the time to discuss this controversy.
How you use hydroquinone will depend on how safe Hydroquinone is.  
For over fifty years, hydroquinone has been used in teeth whitening. 
Hydroquinone has even been exposed to humans through industrial and photography development.  
Reportedly, there have been no known reports of anyone developing cancer because of hydroquinone.

Learn More About Melasma
Studies show that hydroquinone works well as a treatment for melasma, helping to reduce skin discoloration and make blotchy, uneven patches of skin more consistent. 
However, it’s far from the only treatment available for melasma and other pigmentation-related skin conditions.
Our guide to melasma goes into more detail on how and why melasma occurs, as well as the most effective treatments available for reducing hyperpigmentation and returning your skin to normal.

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