Mixed news on hair dyes and cancer risk

Science News, Feb 5, 1994 by K.A. Fackelmann

In this era of cancer scares at every turn, a new study offers women mostly reassuring news about the cancer risk of hair dyes.

The large study finds that most women who use permanent hair coloring do not face an increased risk of fatal cancers. The research does, however, uncover a link between very prolonged use of black hair dye and two immune system cancers.

Hair colorings contain substances similar to the chemicals in coal tar that cause cancer in laboratory animals. Yet studies of the link between hair dyes and human cancer have proved inconclusive.

Most previous research efforts involved asking volunteers who already had cancer about their hair-coloring habits, a retrospective approach that can skew findings. Furthermore, past studies often focused on a small number of participants and thus lacked the statistical muscle to pick up an association between hair coloring products and malignant tumors in a specific subgroup.

To help get a clearer idea of cancer risk, Michael J. Thun of the Atlanta-based American Cancer Society and his colleagues embarked on a large-scale pro, spective study that queried healthy women about their use of permanent hair dye. The researchers collected information on 573,369 women enrolled in a study of cancer mortality. About one-third of the women used permanent hair dye, the investigators reported in the Feb. 2 JOURNAL OF THE NATIONAL CANCER INSTITUTE.

A statistical analysis revealed that women who reported any use of permanent hair-coloring products actually showed a slightly lower risk of all fatal cancers than women who had never used such dyes. That finding underscores the belief that such products generally do not increase the risk of cancer, Thun says.

"I think we can rule out hair dyes as a major [cancer] concern," adds epidemiologist Graham A. Colditz of the Harvard Medical School and Brigham and Women's Hospital in Boston. Colditz wrote an editorial accompanying the new study.

These data are "reassuring," comments epidemiologist Shelia Hoar Zahm of the National Cancer Institute in Bethesda, Md. However, Zahm is quick to point out that this new study does add to evidence suggesting that hair colorings can pose specific cancer risks to a select group of women.

For example, Thun and his colleagues found that, compared to women who didn't color their hair, women who used permanent black hair dye for 20 years or longer ran about a four times greater risk of dying from non-Hodgkin's lymphoma, a cancer of the lymph tissue, or multiple myeloma, a malignancy of the bone marrow cells that produce antibodies.

That finding is consistent with an earlier study by Zahm and her colleagues. The team found that using hair-coloring products (particularly the darker colors) heightened a woman's risk of developing non-Hodgkin's lymphoma and multiple myeloma. That study, in the July 1992 AMERICAN JOURNAL OF PUBLIC HEALTH, revealed that semipermanent hair coloring products also raise the risk of such immune system cancers.

It could be that dark hair dyes contain higher concentrations of mutagenic chemicals and thus are associated with a greater risk of these specific cancers, Zahm notes. The skin absorbs the chemicals in hair colorings during the application process, she adds.

Another hint that hair-coloring products may lead to non-Hodgkin's lymphoma--and certain other cancers--comes from a study of hairdressers conducted by epidemiologist Paolo Boffetta of the International Agency for Research on Cancer in Lyon, France.

Boffetta's team studied the incidence of non-Hodgkin's lymphoma and ovarian cancer among women who worked as hairdressers in four European countries. The team discovered no overall pattern of risk; however, Danish hairdressers had an increased risk of both ovarian cancer and non-Hodgkin's lymphoma. Boffetta and his coworkers report their findings in the January JOURNAL OF OCCUPATIONAL MEDICINE.

Still, the evidence that on-the-job exposure to hair dye boosts the risk of such cancers remains far from conclusive, Boffetta says.

The full story of cancer risk and hair-coloring products remains of considerable importance to people who work in beauty salons and to women who rely on such products, Zahm says. "We have an exposure here that we know is carcinogenic in animals," she says. "We need further research."