Mercury, long known as a toxic substance, is making a comeback in skin products, and dermatologists should familiarize themselves with both the dangers and the availability of this all-too-common cosmeceutical ingredient.

The ancient Egyptians and Romans used mercury to lighten the skin and in a variety of ointments, and the Greeks and Egyptians used it to treat skin infections (Environ. Health Perspect. 2002;110:11-23).

While versatile and used for diverse purposes for many years, such as in thermometers and in dental amalgams, mercury and its related compounds have long been known to be extremely toxic and should be avoided in food and skin care. Indeed, the wide-ranging adverse health effects of mercury-containing skin-lightening products have been known since the early 1970s (Arthritis Rheum. 2007;56:1721).

While mercury has been banned in skin care products sold in the United States since 1990, it is found in numerous skin-lightening agents sold elsewhere. In Europe, such a ban was enacted in 1976. Recently, some of these products have made their way onto U.S. shelves and, to the surprise of many, have been reported to contain toxic levels of mercury. This column will review some of the latest data on mercury-containing skin products and describe the current emerging controversy.

Renewed Popularity

Skin-lightening agents that contain mercury have become increasingly popular in recent years, especially among women with dark skin (Biometals 2004;17:167-75). In particular, skin-lightening cosmetics that contain hydroquinone, mercury, and/or corticosteroids are used widely in many African countries, and especially in sub-Saharan Africa (Med. Trop. 2007;67:627-34). While effective as a whitening agent, mercury is a toxic heavy metal that can produce deleterious effects on humans, through ingestion, skin contact, or inhalation.

The primary vectors for exposure have been metallic or elemental mercury in dental amalgams, ethylmercury in the form of thimerosal in vaccines, and methylmercury in seafood. Metallic mercury also is found in thermometers, organic mercury is used in paints and fungicides, and inorganic mercury compounds are used in medicinal and skin care formulations. The present surge in the use of mercury in skin-lightening formulations, as well as in some religious rituals, has added avenues for mercury exposure (Biol. Trace Elem. Res. 2009;131:43-54; Crit. Rev. Toxicol. 2006;36:609-62; J. Pediatr. Health Care 2007;21:307-14; Int. J. Dermatol. 2008;47:344-53; Environ. Health Perspect. 2002;110:11-23; Rev. Environ. Health 2005;20:39-56; Br. J. Dermatol. 1968;80:623-4).

Some researchers have noted that in Africa, percutaneous absorption is facilitated by the conditions under which these products are used, that is, for long periods, over a large body surface area, and in hot, humid weather. Palmer et al. showed in a human in vitro model that mercury was readily absorbed in the skin in a comparison between an aqueous formulation, which exhibited a significantly higher rate and further extent of absorption, and a proprietary formulation. Their study was prompted partly by the popularity of the mercurous chloride–containing beauty cream Crema de Belleza-Manning, a popular agent used to lighten and smooth the skin and to treat acne. The cream has been linked to elevated urinary mercury levels in hundreds of people in the southwestern U.S. border states (J. Toxicol. Clin. Toxicol. 2000;38:701-7).