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Does Hydroquinone Have a Dark Side?

They were once mistakenly thought to be caused by a disease of the liver, so they are called “liver spots.” Actually these skin blemishes are caused by a buildup of the skin pigment melanin and are associated with aging and long-term exposure to ultraviolet light.

They were once mistakenly thought to be caused by a disease of the liver, so they are called “liver spots.” Actually these skin blemishes are caused by a buildup of the skin pigment melanin and are associated with aging and long-term exposure to ultraviolet light. Technically referred to as “Lentigo senilis,” these hyperpigmented spots usually just present a cosmetic problem unless they develop irregular borders and undergo a colour change, in which case they need to be evaluated by a physician. People bothered by such “senile freckles” can look to hydroquinone for help.

When applied as an ingredient in a skin cream, this chemical inhibits the activity of tyrosinase, an enzyme that is necessary for the formation of melanin. This brings up three questions. How well does hydroquinone work, what concentration is needed, and what risks, if any, does its use present? Hydroquinone does work, and its efficacy, as is to be expected, is dose related. Need a minimum of 1% in a cream to see any result, and really significant effects kick in at 4%. In the U.S., hydroquinone is available in over the counter products at concentrations up to 2%, anything more than that requires a prescription. In Europe and in Canada all hydroquinone products require a prescription. Why the difference?

Different regulatory agencies arrive at decisions in different ways. In this case, Europe and Canada look at worst case scenarios while the U.S. evaluates hydroquinone based on its actual use in cosmetics. Rat feeding studies have suggested that hydroquinone may be carcinogenic, although this is contentious. In humans, in rare cases, accidental ingestion of photographic developer fluid containing hydroquinone has resulted in toxic reactions, but in a controlled trial with human volunteers, ingestion of 300-500 mgs daily for months produced no observable effects. As far as topical application goes, no systemic reaction has ever been noted, and no link to skin cancer has ever been found. But there is a chance of skin irritation, especially if sun protection is not used after application, as well as a rarely seen blue discoloration known as “ochronosis.” With higher concentrations there is the possibility of losing too much pigment resulting in white spots. It is mainly for the latter reasons, and some concern that hydroquinone has not been studied with enough rigour, that Canada and Europe are concerned about over-the-counter availability.

But aside from hydroquinone products that have been adulterated with mercury compounds, which has happened in Africa, no significant problems with 2% solutions have cropped up. Hydroquinone also occurs in nature, found in the bearberry, madder and mulberry plants, extracts of which are touted as “natural skin lightening agents.” These do work, but whatever issues arise with hydroquinone apply to these preparations as well. The fact that the hydroquinone comes from a natural source is irrelevant. Basically, 2% hydroquinone preparations, no matter what the source, can reduce age spots effectively and the alarm sounded by some activist organizations about such products is not backed up by evidence.