It’s OK to Wash Away the Gray

It’s OK to touch up the gray. A study of 99,000 women has found no evidence that long-term use of hair dye can cause certain types of cancer.

“The totality of evidence today is far more reassuring than alarming about any hazards of hair dye use,” Dr. Charles H. Hennekens, head of the preventive medicine department at Harvard Medical School and co-author of the study, said Tuesday.

Hennekens said that a study of nurses ages 30 to 55 found that over a 14-year period there was no increase in what are called hematopoietic cancers among those who used permanent hair dye. Hematopoietic cancers include leukemia, multiple myeloma, Hodgkin’s disease and non-Hodgkin’s lymphoma.

A report on the study is to be published today in the Journal of the National Cancer Institute.

The new study is the largest yet on the issue of cancer and hair dye, and it is statistically more powerful than most earlier work because the women were interviewed about their lifestyles before getting any disease and then were followed for years.

Hennekens said most earlier research that had found some association between hair dye and cancer were retrospective studies in which women who had cancer were asked to recall things about their diets, smoking and cosmetic use. He said those studies are weaker because the conclusions depended upon the memory of people who are seeking reasons for their illness.

Recent studies sponsored by the American Cancer Society also have found no association between hair dye and cancer.

Hennekens did acknowledge that some laboratory studies showed that some mice painted with hair dye did develop tumors, although the numbers of mice with the cancers were only slightly above normal.

“It is not clear the precise relevance of these animal studies to humans,” he said.

Dr. Francine Grodstein, a researcher at the Harvard School of Public Health and a co-author with Hennekens of the Journal study, said the only possible exception to the general conclusion about hair dye safety is for women who use black hair dye for more than 20 years.

She said there is a suggestion in some studies that there may be a very slight increase in some cancers among these women, but that even this conclusion is uncertain and needs more study.

“This is a very small number of women, a subgroup within a subgroup,” Grodstein said. “For the vast majority of hair dye users, there is no problem.”

Grodstein said that questionnaires used in her study asked about use of hair dye but did not ask about the color used. But the researchers did analyze the study data for women with naturally dark hair--those most likely to use black hair dye--and found no statistical evidence that they had more cancer than any of the other women in the study, Grodstein said.

Still, she said the study concludes that “further investigation of the dark hair dyes and hematopoietic cancer is warranted.”