Hydroquinone’s reputation precedes it. First discovered as a powerful photographic developing agent in 1880 by Sir William de Wiveleslie Abney, Hydroquinone eventually made its foray into skincare, gaining popularity as a skin-lightening ingredient in such regions as Africa and Asia. But its possible side effects—burning, redness, permanent discoloration—and the conversation surrounding the societal pressure on women to bleach their skin have made the ingredient a controversial additive to beauty products.
Today, you can find hydroquinone available in up to 2% concentration over the counter (often as an ingredient in skincare products, like serums) or above 2% strength by prescription. Hydroquinone is often used in skin conditions that cause melanin hyperpigmentation, such as traumatic scars, acne scars, age spots, freckles, melasma and lentigines.
Hydroquinone lightens the complexion by reducing the number of melanocytes (cells that incite melanin production and are responsible for pigmentation) in the skin. “The ingredient acts by suppressing an important enzymatic reaction in the melanocytes that prevents the conversion of tyrosine to dihydroxyphenylalanine, and this ultimately leads to a reduction in the amount of melanin in the skin,” says Dr. Aranmolate. This process is reversible, and exposure to sunlight or ultraviolet light will cause rebound hyperpigmentation and darkening of bleached areas.
Classified as a skin allergen and potentially dangerous, hydroquinone has been banned in the European Union, Japan and Australia. Chronic, long-term use of hydroquinone has also been linked to an increased risk in the development of disorders such as ochronosis. “Ochronosis is a syndrome caused by the accumulation of homogentisic acid [which is associated with the production of brown pigment] in connective tissues,” says Dr. Aranmolate. “This often leads to hyperpigmentation and ‘caviar-like’ lesions on the skin.”
In addition to its potential side effects, hydroquinone has come under scrutiny due to reports of products containing the ingredient also being laced with mercury, making them extremely poisonous and even life-threatening.
It’s been confirmed that mercury in high levels is toxic for humans, but the jury is still out as to whether hydroquinone is unsafe.
Although some concerned individuals are asking to have hydroquinone reevaluated by the FDA (Dr. Germain says the agency will likely comply soon), so far there are no peer-reviewed credible studies showing hydroquinone to be unsafe in humans.