Tinted - German consumer magazine investigates hair-dyes
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The German consumer magazine  features a new test report on hair-dyes in its Jan 2004 issue. 40 commercial two-component hair dyes were screened for potentially toxic ingredients - with alarming results: none of the dyes came off well, but all contained one or more substances with an adverse health record. The testers also found resorcinol [CAS RegNr 108-46-3], a phenolic compound, in 33 products. Their concern with these findings was serious enough to discourage from use and to stop further investigations at this point. The publication coincides with major efforts of the European Council to re-assess many "old" chemicals, including aromatic amines that were regularly present as coupler dyes.
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On the "plus" side: testers did not find ortho-phenylene diamine [95-54-5], a known carcinogen (class "B2" = sufficient evidence of human carcinogenicity, according to the EPA 1986 classification) that is listed on most carcinogen lists, e.g. the Californian Proposition 65 List. However, they did find 2,5-toluenediamine [CAS RegNo 95-70-5], a congener of the probable human carcinogen 2,4-toluene diamine [CAS RegNo 95-80-7] (also classified as "B2").
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The toxicological role of resorcinol (meta-dihydroxybenzene) in hair dyes has yet to be defined. The compound has been shown to exert irritant and toxic effects with rabbit skin and has been found mutagenic in several mutation assays. However, human data is inadequate and awaits re-evaluation.
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The magazine's comments point to current problems with risk assessment of chemical substances: there have been many examples where aromatic amines have been shown to be allergenic, mutagenic, carcinogenic, or teratogenic. The key question is if this is a class effect. Hardly surprising, industry representatives insist that structural isomers may have totally different chemical and biological properties. More sceptical reseachers point out that the simple lack of studies that demonstrate an adverse health effect may be insufficient even after repeated tries, because the chosen test system may be inadequate. A more serious argument, however, is the fact that modern hair dyes which are administered as two or more components transfer a chemical "laboratory" to scalp and skin that is now being exposed to reactive intermediates of unkown toxicity. The regular presence of detergents may exacerbate the problem by allowing increased penetration across the exposed skin.
My conclusion: "exposure minimization" may be a wise measure to avoid problems.
11:50:51 PM 
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