Harvard Women's Health Watch
August 2001

By the Way, Doctor
Q Can you tell me if hair dye can cause cancer?

A This question has been asked for several decades, but the answer is still up in the air. Scientific interest in such a link is grounded in the carcinogenic effects of some hair dye ingredients in laboratory animals. In the 1970s, several reports suggested that hairdressers and cosmetologists, groups that have the most exposure to hair dyes, were especially prone to developing cancers of the blood and lymph systems — specifically, multiple myeloma, non-Hodgkin's lymphoma, and leukemia.

In 1993 researchers from the National Institute of Environmental Health Sciences reported that using hair dyes increased a person's risk of developing leukemia by 50%, and use for 16 years or more increased it by 150%. Also that year, researchers from the Harvard School of Public Health and the University of Athens Medical School announced evidence of another link. They reported that women who dyed their hair one to four times a year had a risk of developing ovarian cancer 70% greater than that of women who never used hair coloring. Women who used hair dye five times per year had a 100% greater risk.

Early in 1994, the American Cancer Society joined forces with the Food and Drug Association (FDA) to try to resolve this question. Their researchers analyzed questionnaires from 573,369 women in a cancer-prevention study and determined that for most women, using permanent hair coloring did not increase the likelihood of dying from cancer. The exception was women who used black hair dye for more than 20 years. They had a slightly increased risk of dying from non-Hodgkin's lymphoma or multiple myeloma. In this investigation, researchers looked only at women who died during the study; they did not evaluate how many were diagnosed with cancer during the study period.

But a report from the Nurses' Health Study (NHS) — also in 1994 — failed to find any connection between use of hair dye and leukemia, lymphoma, or multiple myeloma. During 1976-82, almost 100,000 women participating in that investigation answered questions about their hair dye use and natural hair color. During the follow-up period, which ended in 1990, the rate of these cancers was about the same for all of the women, regardless of whether they used hair coloring or what their natural hair color was.

The topic arose again this February, when researchers from the University of Southern California reported a link between the use of permanent hair coloring and bladder cancer. They analyzed questionnaires from 897 patients with bladder cancer and compared them to questionnaires from 897 similar individuals without bladder cancer. They found that individuals with bladder cancer were three times as likely to have used permanent hair dyes at least once a month for 15 years or more. In addition, subjects who worked for 10 or more years as hairdressers or barbers were five times more likely to have bladder cancer than people who were not exposed to permanent hair dye. There was no association between temporary or semi-permanent dyes and the risk of bladder cancer.

None of these studies contain detailed information about the specific coloring products used or their ingredients. Moreover, these epidemiologic investigations were designed to uncover possible associations between lifestyle habits (hair dye use) and health outcomes (cancer or death from cancer). They do not demonstrate cause-and-effect relationships. To determine whether using hair dye increases cancer risk would require a controlled trial in which thousands of women were randomly assigned to use a specific hair dye or to refrain from coloring their hair. If a significantly larger number of women who used hair dye developed cancer (after researchers had taken into account other influences, such as smoking or exposure to toxins), the hair dye would be regarded as a cause of cancer. For ethical reasons, such a study is unlikely to occur.

Taken together, the evidence is insufficient for scientists to state with certainty whether there is a link between using hair dye and cancer. Such an association, if it exists at all, has been suggested only for those who use dark or permanent dyes. If you use dark hair coloring and want to play it safe, try to use it as infrequently as possible. Wear gloves when applying the dye, don't leave it on your scalp any longer than necessary, and rinse your scalp thoroughly after using it. And choose products that contain henna, which is largely plant-derived, or lead acetate, used to darken hair gradually. The ingredients of both have been tested for safety in accordance with FDA requirements.

Celeste Robb-Nicholson, M.D.

REFERENCES
Gago-Dominguez, M et al. (2001). Use of permanent hair dyes and bladder-cancer risk. International Journal of Cancer 91(4): 575-579.

Grodstein, F et al. (1994). A prospective study of permanent hair dye use and meatopeietic cancer. Journal of the National Cancer Institute 86(19): 1466-70.

Meadows, M. (January-February 2001). Heading off hair-care disasters: use caution with relaxers and dyes, FDA Consumer.

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