Occupational exposures of hairdressers and barbers and personal use of hair colourants.

Throughout history and across cultures, women as well as men have felt the need to change the natural colour of their skin, lips and hair, or to restore the colour of greying hair. For thousands of years, cosmetic dyes have been a part of all human cultures. The use of hair dyes can be traced back at least 4000 years; evidence from royal Egyptian tombs suggests the use of henna for dyeing of hair and fingernails. Henna contains the dye Lawsone (2-hydroxy-1,4-naphthoquinone), which, in its pure form, is also used as a synthetic direct (semi-permanent) hair dye. In the days of the Roman Empire, grey hair was darkened by combing it with lead combs dipped in vinegar. Interestingly, it has recently been shown that this application produces darkening of grey hair by deposition of lead sulfide nanoparticles (diameter of about 5 nm) on the surface of the hair (Walter et al., 2006; Nohynek et al., 2004a). Traditional, lead acetate-based products for darkening grey hair are still found on the international market, although their importance is minor. Today, millions of consumers use a large variety of cosmetic dyes and pigments to change the appearance of their skin, lips, nails or hair. Hair dyeing has become a common practice in modern industrialised societies; the hair-dye industry has estimated (unpublished data) that between 50 and 80% of women have used hair dyes in the USA, Japan and the European Union. During the last century, synthetic dyes have taken a pivotal role in hair colouration. Their chemistry, use and safety have been reviewed (Corbett 1999, 2000; Corbett et al., 1999; Nohynek et al., 2004a; Zviak & Millequant 2005a,b).