Women who dye their hair may be increasing their risk of cancer, scientists warn.
Those who use hair dyes more than nine times a year have a 60 per cent greater risk of chronic lymphocytic leukaemia, a study suggests.
Women who regularly used hair dyes before 1980 could be in even greater danger, with a 70 per cent increased risk of developing the blood disease.
This is because dyes sold before then contained toxic ingredients linked to cancer which are not present in modern hair products.
The research also suggests the risk of developing another type of cancer is increased by dark colours.
Women who use dark hair dyes are 50 per cent more likely to develop follicular lymphoma, a non-aggressive blood cancer.
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 US.
They analysed four studies conducted between 1988 and 2003. Of the patients involved, 4,461 had follicular lymphoma and 5,799 did not.
They were asked detailed questions about their hair dye use and other potential risk factors.
Dr. Zhang said the results answered the inconsistencies between previous studies, some of which found no link between hair dye use and cancer.
These inconsistencies could be explained by genetic differences between the patients involved affecting their risk of cancer, she claimed.
The study follows a report from the International Agency for Research on Cancer last month which found hairdressers and barbers were “probably” at greater risk of bladder cancer.
But it said there was not enough evidence to decide whether the personal use of hair dyes increases the risk.
Jamie Page, chief executive of the charity the Cancer Prevention & Education Society, said: “For some time now links between hair dyes and cancer have been known.
“It is important that people are aware that many chemicals in consumer products have not been adequately tested for safety.
“It is absolutely vital that regulatory authorities require that all product ingredients have been properly tested for safety before allowing them to be used by the general public as well as workers such as hairdressers.”
Hair dye manufacturers insist their products are among the most thoroughly tested on sale. “The News”