Hair dyes may cause cancer - and hairdressers and barbers could especially be at risk because of their daily contact with the colourants.
Hairdressers face "a small but consistent risk of bladder cancer", and the dyes may also be responsible for an increased risk of lymphoma and leukaemia. Researchers aren't sure if people who dye their hair at home are also at risk.
Hair dyes were supposed to be safe after known carcinogens were removed in the 1970s, but the latest review from the International Agency for Research on Cancer suggests that hairdressers are still at risk. The dyes, they concluded, were "probably carcinogenic to humans".
Dark hair dyes are believed to come with the greatest cancer risk.
(Source: Lancet Oncology, 2008; 9: 322-3).