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Hair Dye May Raise Cancer Risk: Study
Women who have been colouring their hair for 24 years or more have a higher risk of developing a cancer called non-Hodgkin lymphoma, US researchers report.
They said their study of 1,300 women could help explain a mysterious rise in the number of cases of the cancer that affects the lymphatic system.
Writing in the American Journal of Epidemiology, they said women who dyed their hair starting before 1980 were one-third more likely to develop non-Hodgkin lymphoma (NHL) and those who used the darkest dyes for more than 25 years were twice as likely to develop the cancer.
"Women who used darker permanent hair colouring products for more than 25 years showed the highest increased risk," Tongzhang Zheng, associate professor of epidemiology and environmental health at Yale School of Medicine, said in a statement.
Cancer experts note that a person's absolute risk of developing lymphoma is very low, so doubling that risk still means a woman who dyes her hair is very unlikely to develop lymphoma.
The American Cancer Society says NHL will affect an estimated 54,000 Americans this year and will kill 19,000.
It affects slightly more men than women.
The incidence of NHL has doubled since the mid-1970s and no one knows why.
Experts suspect exposure to chemicals can be a factor.
The lymphatic system is part of the immune system, so people with immune weaknesses are at special risk, notably AIDS and organ transplant patients.
Dr Zheng and colleagues studied 600 Connecticut women who had NHL.
They were asked to specify what hair colouring products they might have used and when.
They were compared to 700 healthy women.
The Yale University researchers did not find any larger risk of cancer in women who started using hair dye in 1980 or later.
"This could reflect the change in hair dye formula contents over the past two decades, or indicate that recent users are still in their induction and latent period," Yawei Zhang said, who also worked on the study.
"Hair colouring products have undergone tremendous change over the last 20 years," Dr Zheng said.
"Since 1980, many carcinogens have been removed from some formulas, which vary depending on whether the dye is permanent, semi-permanent, darker or lighter."