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Study Links Some Hair Dyes to Kind of Cancer
Published: January 24, 2004
Scientists have found more evidence for a possible link between non-Hodgkin's lymphoma and long-term use of dark hair dye. A study of more than 1,300 women in Connecticut shows that those who began coloring their hair before 1980 increased their chance of developing the disease by 40 percent.
And among those who used permanent rather than nonpermanent dyes, who chose dark colors — browns, reds and black — and who dyed their hair frequently (eight times a year or more) for at least 25 years, the risk doubled, said Dr. Tongzhang Zheng, a Yale epidemiologist who led the study. The results are published in the current issue of the American Journal of Epidemiology.
"For those who used light colors, there was no such increase in risk," Dr. Zheng noted.
Nor was there significantly increased risk among women who used nonpermanent dyes. The difference between permanent and nonpermanent dyes is that permanent ones are mixed with an oxidizing agent. In that process, new chemicals are created, some of which may be carcinogenic, Dr. Zheng said.
Non-Hodgkin's lymphoma is a form of cancer that begins in the body's lymph system. The average American woman has a 1-in-57 chance of developing the disease in her lifetime, according to the American Cancer Society. For a man, the chance is 1 in 48.
Suspicions that hair dyes might increase cancer risk have been around since the 1970's, said Dr. Eugenia Calle, the cancer society's director of analytic epidemiology, but studies over the years have found no connection between the dyes and most forms of cancer.
The Yale researchers and the National Cancer Institute are now looking into whether there are any genetic influences that might make certain women more likely to develop lymphoma after exposure to dye.
Because all the studies done so far, including the latest one, have been observational rather than clinical, their findings do not provide evidence that hair dye causes lymphoma, said Gerald McEwen, vice president for science at the Cosmetic, Toiletry and Fragrance Association, a trade group in Washington.
"There's no smoking gun here," Mr. McEwen said, "no causal relationship."
In this study, the researchers found no increase in cancer risk among women who started dying their hair after 1980, no matter how frequently they did so or what color they used. In the late 1970's, hair dye makers stopped using certain coal-tar ingredients that had been found to cause cancer when fed to laboratory rats and mice.
"This is the first study that's been able to look at the time period after 1980," said Dr. Shelia Hoar Zahm, deputy director of cancer epidemiology and genetics at the National Cancer Institute, who collaborated on the study. "It suggests that the later formulations are safer. If the risk is limited to those people who started use before 1980, it means we're really in better shape now."
Another possibility, however, is that women have not had time to use the new products long enough for them to have any adverse effect, Dr. Zheng said. "It's very hard for us to say that now the products are safe," he said.
Previous studies on the association between hair dye and non-Hodgkin's lymphoma have been mixed. A few have shown no association, but two, one done in 1988 and one in 1992, have suggested that there may be a link.
If hair dye does play some role in lymphoma, Dr. Calle said, it would make sense that the darker colors, which have greater concentrations of ingredients, would have the strongest effect.