Hydroquinone has quite a reputation. Discovered as a potent photographic developing agent in 1880 by Sir William de Wiveleslie Abney, it eventually ventured into skincare, becoming a popular skin-lightening ingredient in regions like Africa and Asia. However, its potential side effects – including burning, redness, and permanent discoloration – along with the discourse around societal pressure on women to lighten their skin, have made it a controversial addition to beauty products. Nevertheless, many dermatologists deem it a prime lightening solution, provided it is used responsibly.
What is hydroquinone and what does it do?
Currently, hydroquinone can be found in up to 2% concentration without a prescription (often as an element in skincare products, such as serums), or at a strength above 2% with a prescription. “Hydroquinone is frequently utilized in skin conditions causing melanin hyperpigmentation, like traumatic scars, acne scars, age spots, freckles, melasma, and lentigines,” states Dr. Sheg Aranmolate, a Nashville-based physician and the founder of Leovard Skincare.
Hydroquinone brightens the complexion by reducing the quantity of melanocytes (cells that stimulate melanin production and are accountable for pigmentation) in the skin. “The ingredient functions by suppressing a crucial enzymatic reaction in the melanocytes that hinders the conversion of tyrosine to dihydroxyphenylalanine, and this ultimately results in a decrease in the amount of melanin in the skin,” explains Dr. Aranmolate. “This process is reversible, and exposure to sunlight or ultraviolet light can cause rebound hyperpigmentation and darkening of bleached areas.”
The reason hydroquinone is still regarded as the ultimate choice among skin-lightening options on the market lies in its potency. “While there are numerous other ingredients available for [skin lightening], none works nearly as effectively as hydroquinone because many of them are cosmetic active ingredients, while hydroquinone is a drug active ingredient,” remarks Dr. Marguerite Germain, a dermatologist in Charleston, South Carolina. Drug active ingredients, like hydroquinone, are those that have been listed by the government as approved skin-lightening medications and have undergone extensive safety and efficacy tests to be sanctioned by the U.S. Food & Drug Administration (FDA) as pharmaceutical active ingredients (drugs). According to the FDA, a drug's intended use is “to treat or prevent disease or otherwise influence the structure or functions of the human body.”
Cosmetic active ingredients, on the contrary, are defined by their intended use: “articles intended to be rubbed, poured, sprinkled, or sprayed on, introduced into, or otherwise applied to the human body…for cleansing, beautifying, promoting attractiveness, or modifying the appearance,” as per the Federal Food, Drug, and Cosmetic Act. Essentially, cosmetic active ingredients cannot claim to alter the structure of the skin, as drug active ingredients can.
Other popular, non-hydroquinone lighteners (considered cosmetic active ingredients) encompass kojic acid, arbutin, bearberry, hexylresorcinol, phenylethyl resorcinol, tranexamic acid, and azelaic acid, but Dr. Germain warns against their skin-lightening assertions. “Some cosmetics marketers who are not authorized to sell drug products will exaggerate the potential side effects of hydroquinone, as they can't sell it – [but] the alternatives don't perform as well.”
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The potential side effects of hydroquinone
Classified as a skin allergen and potentially hazardous, hydroquinone has been prohibited in the European Union, Japan, and Australia. “We have discovered that perhaps 16–17% of patients have a sensitivity to hydroquinone, whether [as] an irritant or an actual true allergy,” elaborates Dr. Suneel Chilukuri, a dermatologist in Houston. “It's challenging to define, but we know that hydroquinone can actually worsen your pigmentation [if you are allergic to it] due to the existing inflammatory response.”
Chronic and long-term utilization of hydroquinone has also been associated with an elevated risk of developing disorders such as ochronosis. “Ochronosis is a syndrome caused by the accumulation of homogentisic acid [which is related to the production of brown pigment] in connective tissues,” says Dr. Aranmolate. “This frequently leads to hyperpigmentation and ‘caviar-like’ lesions on the skin.” According to a study in the Indian Journal of Dermatology, the initial reports of ochronosis were found in South Africa, where the skin disorder was described in 28–35% of the black population. Initially, it was believed that ochronosis was only reported among dark-skinned African individuals, but subsequent reports indicated that fair-skinned people, including Europeans and Hispanics, were also affected by the condition. Currently, the condition is rarely reported in the U.S., perhaps due to stricter dosage regulations.
Hydroquinone’s association with mercury
In addition to its potential side effects, hydroquinone has come under examination due to reports of products containing the ingredient also being laced with mercury, making them extremely toxic and even life-threatening. “Mercury is a poisonous and inexpensive ingredient that can lighten the skin while also harming the kidneys and the nervous system,” says Dr. Michelle Henry, a dermatologist in New York City. The FDA has banned mercury-containing skin bleaches, but they still enter our market (often from overseas) and have been linked to recent mercury-poisoning cases. Although both hydroquinone and mercury are used as skin-lightening agents, it is mercury that has been proven to cause harm to the human body when consumed or absorbed in large quantities.
Still, for those residing in societies that value lighter skin tones, the pressure to conform (even at the risk to their health) is significant. There are multiple ethnic groups “that genuinely desire to lighten their skin, as having fair skin is more of a status symbol,” explains Dr. Chilukuri. “It implies that you're not a worker [under the sun], so there's a considerable amount of psychology involved – the fairer your skin, the more attractive you are considered in those cultures.”
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The bottom line
It has been confirmed that high levels of mercury are toxic to humans, but the verdict is still pending on whether hydroquinone is unsafe. “Laboratory studies on bacteria and animal cells have indicated that hydroquinone has some carcinogenic and mutagenic effects, but these effects have yet to be documented in human studies,” says Dr. Aranmolate. In one study, rats were directly fed hydroquinone over a period of time and experienced no adverse effects. In another study, human volunteers ingested up to 500 mg per day for five months, with no negative consequences. “Topically, in facial application, less than 200 mg is applied to the skin – and most of it is not absorbed by the skin,” says Dr. Germain. “Two hundred milligrams is 2,500 times less than [what] was ingested in the human safety study.” Scientific testing and the ingredient's long history of use demonstrate that hydroquinone is safe when used as directed or under a doctor's supervision. Although some concerned individuals are requesting that the FDA reevaluate hydroquinone (Dr. Germain states that the agency is likely to comply soon), as of 2024, there are no peer-reviewed reliable studies indicating that hydroquinone is unsafe for humans.
