Examining the Link Between Hair Chemicals and Cancer

Does using chemical hair care products, particularly among women, increase the risk of developing cancer? A new study appearing in Carcinogenesis (doi:10.1093/carcin/bgx060) indicates that it might. The possible health risks of using hair care products affects much of the population. According to the National Cancer Institute, more than one-third of women older than 18 years—and about 10% of men older than 40 years—use hair dye. Those products contain more than 5,000 chemicals; some cause cancer in animals. According to NCI, “Given the widespread use of hair dye products, even a small increase in risk may have a considerable public health impact.” Using data from the Women’s Circle of Health Study—a case–control study in New York City and 10 counties in New Jersey—researchers asked women about using dye, chemical relaxers, and deep conditioning creams that contained cholesterol or placenta. The participants included 2,280 breast cancer case patients (1,508 black and 772 white) and 2,005 control subjects (1,290 black and 715 white). Researchers analyzed their use of the products with respect to the subjects’ breast cancer risk and whether the risks varied by estrogen receptor status. The authors then compared the use of hair products between women who did and did not develop breast cancer. More white women than black women use hair dye (58% vs. 30%), whereas relaxer was much more common among black women (88% vs. 5%). The results show associations between using hair dyes (especially darker shades) as well as chemical relaxers or straighteners and increased risk of breast cancer, with some differences by race. According to the Carcinogenesis study, using hair dye was not associated with breast cancer overall among white women even with their higher exposure. However, using hair dye was associated with breast cancer among black women, despite their having lower exposure. Specifically, the researchers found among black study subjects, more of the cancer patients reported they had used darker shades of hair coloring than the controls. Specifically, light shades were used by 140 (9.3%) of the cancer subjects, and 133 (10.3%) for controls, while medium shades were used by 123 (8.2%) of the cancer cases versus 119 (9.2%) of controls. The numbers skewed much higher for dark brown and black shades between the black subjects. Darker shades were used by 242 (16.1%) of the cancer patients versus 138 (10.7%) for controls. “Women use a variety of hair products and other cosmetics and personal care products, and many often don’t consider the possibility that exposure to these products could be harmful.” By contrast, of the 1,487 white study participants, fewer cancer patients than controls had never used hair dye (292 versus 302). As with black participants, there were more cancer subjects who had used darker shades of hair dye than controls (100 versus 79), but unlike in black women, this difference wasn’t statistically significant and didn’t suggest an association with increased risk. Of the 648 ER-positive cases found in blacks, study authors believe there’s a noteworthy difference between those who dyed their hair at least twice per year, versus those who did not (126 versus 85). They also found that among women who dyed their hair at least twice per year, white women were twice as likely as black women to have ER negative disease (17 of 68 versus 30 of 247). The lead author of that study, Adana A.M. Llanos, Ph.D., M.P.H., assistant professor of epidemiology at Rutgers School Public Health in Piscataway, N.J., said she was drawn to the topic because of the dearth of data available on the link between using hair products and breast cancer risk, especially in black women. “Women use a variety of hair products and other cosmetics and personal care products, and many often don’t consider the possibility that exposure to these products could be harmful,” Llanos said. But much of the epidemiologic data available linking hair dye use and breast cancer risk have focused predominantly on white women. “As a black woman, I hypothesized that differences in prevalence and patterns of hair product use could partly explain some of the racial differences in breast cancer risk and generate new hypotheses for further analysis,” she said. The discussion about chemical hair care products and cancer has been around for decades. After finding in 1980 that certain hair dye ingredients caused cancer in laboratory animals and could penetrate human skin, the U.S. Food and Drug Administration required warning labels on packaging. Hair dye companies soon eliminated the guilty ingredients—4-methoxy-m-phenylenediamine; 4-chloro-m-phenylenediamine; 2,4-toluenediamine; 2-nitro-phenylenediamine; and 4-amino-2-nitrophenol—thus reassuring the public that the perceived danger was over. Since then, research has been mostly inconclusive and often has downplayed the risk of hair dyes and other hair care products. Although some studies linked hair dyes with increased risks of non-Hodgkin lymphoma and leukemia, other studies have not supported those findings. Studies of breast and bladder cancer also have yielded conflicting results. The American Cancer Society has said most studies have found no link between hair dye and breast cancer risk. Still, the issue of safety has reemerged in recent years as hair care product use has been strong and steady. Up to 75% of U.S. women use hair coloring products in a range of hues, and industry market firm Technavio predicts that the global hair color market will reach $29.14 billion by 2019, growing by 9% per year. However, study results on safety have continued to be inconsistent, especially regarding black women’s use of the products. For example, researchers performing a study based on the large-cohort Black Women’s Health Study found “no increases in breast cancer risk associated with any categories of duration of hair relaxer use, frequency of use, age at first use, number of burns experienced during use, or type of relaxer used” (Cancer Epidemiol. Biomarkers Prev. 2007;16:1035–7; doi:10.1158/1055-9965.EPI-06-0946). Donna D. Baird, Ph.D., head of the Women’s Health Group at the National Institute of Environmental Health Sciences in Research Triangle Park, N.C., noted that the Carcinogenesis study replicated findings from the Black Women’s Health Study. “This is reassuring, given the high frequency of use in this community.” Although Llanos agrees with the conclusions from the decade-old study, she said, the comparisons between the studies are faulty because her case-controlled study covered a variety of hair care products and cancer, whereas the other focused only on relaxer use. “We cannot conclude from either of these studies that using relaxers or other hair products causes breast cancer, but findings from our study make it clear that exposure to compounds in some hair products (which may be genotoxic and/or endocrine disrupting) warrant further study,” she said. Perhaps the Carcinogenesis study’s most distinct finding is the observed association between using dark hair dye and the risk of estrogen receptor–positive breast cancer; dark hair dye products contain higher levels of chemicals that might be mutagenic or carcinogenic. “This elevated risk seen in the new study for dark hair dye is an interesting finding that needs replication,” Baird said. “We think it’s significant that we found that black women who reported use of dark hair dye shades had an increased risk of breast cancer overall,” Llanos said. “White women who reported use of chemical relaxers/straighteners had an increased risk of breast cancer overall.” Although he doesn’t dispute most of the conclusions of the study, Tongzhang Zheng, M.B., Sc.D., professor of epidemiology at the Brown University School of Public Health in Providence, R.I., questions certain aspects of the analytic method. “The observed increased risk among whites were based on very small numbers,” he said. Baird said she agrees: “The elevated risk associated with relaxer use in the new study for whites was based on a very small sample, since only about 6% of them reported use. Nor was there a dose response with years of use in whites.” Angeline S. Andrew, Ph.D., assistant professor of neurology in the department of community and family medicine at Dartmouth–Hitchcock Medical Center in Lebanon, N.H., said the Llanos study reinvigorates the call for further investigating whether hair care products cause cancer, particularly for dark-colored dyes. Still, she cautioned, “it is important to remember that results of observational studies must be interpreted as ‘associations’ between a lifestyle factor and cancer risk; the causal nature of the relationship with breast cancer still remains to be assessed.”