Work as a hairdresser or barber has been confirmed as a potential carcinogenic influcence, according to a Working Group report of the International Agency for Research on Cancer (IARC), as published in the April 2008 issue of The Lancet Oncology.

Hair dyes are presently classified as permanent, semipermanent, or temporary dyes. The permanent (also called oxidative) dyes represent approximately 80% of the available products. They work by combining two chemical agents — an intermediate and a coupler — which are bound in the presence of peroxide to form the dye molecule. Dark dyes tend to contain the highest concentrations of these coloring ingredients. In the 1970s, after positive cancer tests in rodents, the use of some of these colorants was discontinued.

According to Dr Robert Baan, of the International Agency for Research on Cancer, Lyon, France, and colleagues, many new epidemiological studies on cancer in hairdressers, beauticians, and barbers have been published since 1993, the date of the last IARC assessment. “A small, but consistent, risk of bladder cancer was reported in male hairdressers and barbers. Because of few supporting findings by duration or period of exposure, the Working Group considered these data as limited evidence of carcinogenicity and re-affirmed occupational exposures of hairdressers and barbers as ‘probably carcinogenic to humans’.”

They also reviewed the epidemiological studies on the personal use of hair dyes, but this evidence was not adequate for a definitive conclusion about such treatments.

Many other chemicals, like hair dyes, belong to the group of organic molecules known as aromatic amines. Ortho-toluidine, used in many organic production processes including for hair dyes, pigments, and rubber chemicals, is now classified as carcinogenic to humans. Another curing agent, MOCA, which is used as a curing agent in plastics, also has joined this classification.

Carcinogenicity of some aromatic amines, organic dyes, and related exposures
Robert Baan, Kurt Straif, Yann Grosse,Beatrice Secretan, Fatiha El Ghissassi, Veronique Bouvard, Lamia Benbrahim-Tallaa, Vincent Cogliano
The Lancet Oncology, Vol 9, April 2008
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Written by Anna Sophia McKenney