A new study finds that using hair dye more than nine times a year increases the risk of chronic lymphocytic leukaemia (a form of cancer of the blood cells) by 60 per cent. But opinions differ on whether dyeing is that dangerous.

The study had also found that women who regularly used dyes before the Eighties were at even greater risk because older products contained toxic ingredients not found in today's hair products.

Women who used dark hair dyes were 50 per cent more likely to develop another type of blood cancer - follicular lymphoma. (Colours such as black, brown and red are thought to be more risky because it takes more chemicals to make the darker shades).

The research also suggests the risk of developing another type of cancer is increased by dark colours.

If non-permanent dark dyes are used the risk increases to 70 per cent, according to the study reported in the American Journal of Epidemiology.

The research was carried out by an international team of scientists, led by Dr Yawei Zhang of Yale School of Public Health in the U.S.

But hair dye manufacturers insist their products are among the most thoroughly tested on sale. And there is no consensus on the issue.

Hair colouring is hugely popular. In the UK, more than 60 per cent of women and around ten per cent of men colour their hair at some point in their lifetime - either at home or in a salon - according to the Cosmetic Toiletry and Perfumery Association, Daily Mail reports.