Hair Dye

Hair coloring products include a wide range of over 5,000 chemical substances, some of which have been reported to be mutagenic and carcinogenic to animals. Hair dye products may be divided into three categories, that is, permanent, semipermanent, and temporary hair colors. Permanent hair colors are the most popular hair dye products. They may be further divided into oxidation hair dyes and progressive hair dyes. Oxidation hair dye products consist of 1.) a solution of dye intermediates, which form hair dyes on chemical reaction, and preformed dyes, which already are dyes and are added to achieve the intended shades, in an aqueous, ammoniacal vehicle containing soap, detergents, and conditioning agents; and 2.) a solution of hydrogen peroxide, usually 6 percent in water.

The prevalence of use of hair dyes is high among women in industrialized countries with more than half of women above age 18 applying hair dyes in Europe and the United States and around 10 percent among males. Consumers use all major types of hair colorants, which may contain aromatic amines, nitro-substituted aromatic amines, high molecular weight complexes, metal salts, and other. The content of hair dye has changed over the years and recent legislation prevents the use of carcinogenic substances in hair dye use.

Some components of hair dyes may cause skin irritation on certain individuals and a preliminary test according to accompanying directions should first be made as it is generally advised by the manufacturers. A major concern on the health effects of hair dyes is, however, the suspicion that they may be linked to cancer. While no clear excess risk of cancer has been observed among hairdressers and barbers, the evaluation of cancer risk among regular users of hair dyes has been poorly evaluated due to lack of adequate data on humans. In 1992, the International Agency for Research on Cancer evaluated hairdressing and barbering as occupations entailing exposures that are probably carcinogenic to humans; personal use of hair colorants could not at that time be evaluated in terms of its carcinogenicity.

Since this last evaluation, several studies have tried to provide human data on regular use of hair dyes. Among the cancer sites that have been most commonly evaluated in association with regular exposure to hair dyes are bladder cancer and lymphomas. Small amounts of [Page 771]the bladder carcinogen 4-aminobiphenyl (4-ABP), an aromatic amine, in eight out of the 11 hair dyes tested have been identified. Although an excess risk has been seen in some studies that included information on personal use of permanent hair dyes and bladder cancer risk, the overall results are not yet converging.

More than half of women in Europe and the United States above the age of 18 use hair dye products.

Use of hair dyes has been inconsistently associated to the etiology of lymphomas. Recently, Yawei Zhang from Connecticut and Silvia de Sanjose reporting from six European countries have shown that the risk of certain types of lymphomas may increase between 20 to 30 percent among regular users of hair dyes. In both studies, the risk was increased mainly among those women using hair dyes before 1980, but no clear association among those using hair dyes during the last 20 years. This observation suggests that more recent hair dyes may have a safe composition. Further, the evaluation of all available studies in humans estimated a 15 percent increased risk for hematopoietic cancer, 23 percent for Hodgkin's lymphoma, and a 1 percent increased risk for bladder cancer.

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