The largest study of its kind has found no positive association between personal use of permanent hair dye and the risk for most cancers and cancer mortality.
The findings come from the Nurses’ Health Study, an ongoing prospective cohort study of more than 117,000 women who have been followed for 36 years and who did not have cancer at baseline.
The findings were published online on September 2 in the BMJ.
The results “offer some reassurance against concerns that personal use of permanent hair dyes might be associated with increased cancer risk or mortality,” write the investigators, with first author Yin Zhang, PhD, of Harvard Medical School, Boston.
The findings, which are limited to White women in the United States, indicate correlation, not causation, the authors emphasize.
Nevertheless, the researchers found an increased risk for some cancers among hair dye users, especially with greater cumulative dose (200 or more uses during the study period). The risk was increased for basal cell carcinoma, breast cancer (specifically, estrogen receptor negative [ER–], progesterone receptor negative [PR–], and hormone receptor negative [ER–, PR–]), and ovarian cancer.
A British expert not involved in the study dismissed these findings. “The reported associations are very weak, and, given the number of associations reported in this manuscript, they are very likely to be chance findings,” commented Paul Pharoah, PhD, professor of cancer epidemiology at the University of Cambridge (England).
“For the cancers where an increase in risk is reported, the results are not compelling. Even if they were real findings, the associations may not be cause-and-effect, and, even if they were causal associations, the magnitude of the effects are so small that any risk would be trivial.
“In short, none of the findings reported in this manuscript suggest that women who use hair dye are putting themselves at increased risk of cancer,” he stated.
A U.S. researcher who has previously coauthored a study suggesting an association between hair dye and breast cancer agreed that the increases in risk reported in this current study are “small.” But they are “of interest,” especially for breast and ovarian cancer, said Alexandra White, PhD, of the National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, N.C.
Hair dyes include compounds that “are not just potential carcinogens but also act as endocrine disruptors,” she said in an interview.
“In both breast and ovarian cancer, we know that hormones play an important part in the etiology ... so it’s biologically plausible that you would see [these associations in the current study],” added Dr. White, who was approached for comment.
However, she added that, even with the “modest” 20%-28% increase in the relative risk for certain breast cancers linked to a heavy cumulative dose of dyes in the current study, “there doesn’t seem to be any strong association with any cancer type.”
But she also pointed out that the most outstanding risk association was among ER–/PR– breast cancers, which are the “most aggressive and difficult to treat,” and thus the new findings are “important.”
Dr. White is the lead author of a 2019 study that received a lot of media attention because it rang an alarm bell about hair dyes and breast cancer risk.
That study concluded that ever using permanent hair dye or hair straighteners was associated with a higher risk for breast cancer than never using them and that this higher risk was especially associated with Black women. However, the study participants were from the prospective Sister Study. The participants in that study had no history of breast cancer, but they each had at least one sister who did. This family history of breast cancer may represent selection bias.