Hair colour used by millions of people at home may contain powerful cancer causing chemicals, UK scientists have warned.
Researchers say chemicals in permanent hair dyes can react with tobacco smoke and other pollutants in the air to form one of the most powerful cancer-causing compounds known.
With more than a third of women and one in ten men regularly colouring their hair in the UK, the researchers say it is "imperative" that the risk to health is quantified.
However, the cosmetics industry in UK has strongly disputed the claim, the 'Daily Mail' reported.
Scientists at Leeds-based company Green Chemicals who conducted a review of the chemistry surrounding hair dye said that all the information was already available and they simply "joined the dots" to make the link with cancer.
They warn that chemicals called secondary amines, which are either found in all permanent hair dyes or are formed in them, can penetrate the skin and stay on the hair for weeks, months or even years after the dye is applied.
Over time, they could react with tobacco smoke and exhaust fumes, to form highly poisonous carcinogenic chemicals called N-nitrosamines.
These are banned from use in cosmetics. However, the researchers argue that they can still be generated via a simple chemical reaction, the report said.
"At this stage, we can't be sure of the amount of N-nitrosamines produced or the level of risk these compounds pose but it is clear a potential hazard exists," Professor David Lewis, one of the authors of the study, and an expert in the chemistry of various dyes, said.
"In the interest of consumer safety, it is imperative that a thorough and independent investigation is conducted to establish the levels of toxicity of these compounds and the potential risks," said Lewis.
But manufacturers insist that the possibility of the chemical reaction has been long known.
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