Use of permanent hair dye or hair straightening chemicals were both associated with a higher risk for breast cancer than 'never use' — and the risks are particularly pronounced among black women, a new analysis of a 50,000-participant study shows.
"Hair products contain more than 5000 chemicals, including some with mutagenic and endocrine-disrupting properties such as aromatic amines," senior author Alexandra White, PhD, head of the National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina, and colleagues explain.
"Overall, [our] results support the hypothesis that hair dye and straightener use, which are highly prevalent exposures, could play a role in breast carcinogenesis," they conclude.
The study was published online December 3 in the International Journal of Cancer.
Notably, prior findings on the association between hair dye use and breast cancer have been inconsistent. "While a few studies have reported a positive association, many concluded that there was no elevated risk," the authors write.
The prospective Sister Study enrolled 50,884 women aged 35 to 74 years living in the United States and Puerto Rico between 2003 and 2009.
The enrollees themselves had no history of breast cancer but had at least one sister who did.
"Current hair dye and straightener use, defined as use in the 12 months before enrollment, was assessed by questionnaire and was completed by 47,650 participants," investigators write.
Over an average follow-up of 8.3 years, there were 2794 cases of either invasive breast cancer or ductal carcinoma in situ (DCIS) in the cohort.
The authors report that 55% of participants reported using permanent dye at enrollment. Permanent dye use was associated with a 45% higher breast cancer relative risk in black women (hazard ratio [HR], 1.45), and a 7% higher relative risk in white women (HR, 1.07; heterogeneity P = .04). Importantly, neither the use of semi-permanent dye nor temporary dyes increased breast cancer risk.
Among all participants, use of chemical treatments to straighten or relax hair was associated with breast cancer risk (HR, 1.18), with a higher risk associated with increased frequency (P for trend = .02).
Asked by Medscape Medical News to comment on the findings, Stephanie Bernik, MD, chief of breast surgery at Mount Sinai West Hospital in New York City, called the study "provocative" and suggested that it does raise questions as to the safety of permanent hair dyes.
However, "these women already inherently have an increased risk of breast cancer because each woman in the study had a sister with breast cancer," cautioned Bernik, who was not involved with the study.
"Therefore, the results are not conclusive," she emphasized in an email.
More frequent use of hair dye was associated with an even higher relative risk of breast cancer, again among black women. For those who colored their hair at least every 5 to 8 weeks, the risk of breast cancer was 60% higher compared with non-users, and this association was equally true for both dark-colored and light-colored hair dyes.
In contrast, among white women, the relative risk of breast cancer was increased by only 12% with the use of light-colored hair dye; however, the same risk was not seen with the use of dark-colored hair dye.
Almost three quarters (74.1%) of black women in the study reported using some form of hair straightener within 12 months of study enrollment compared with only 3% of non-Hispanic white women.
Indeed, women who used a chemical product to straighten their hair every 5 to 8 weeks had a 31% higher relative risk of breast cancer compared with non-users.
And while non-Hispanic white women were far less likely to use any product to straighten their hair, the increased risk of breast cancer was evident for both black women and non-Hispanic whites, the authors note.
Whereas semi-permanent dye use was not associated with risk, nonprofessional application of semi-permanent hair dye to another person's hair was associated with a 28% increased relative risk of breast cancer.
A higher risk for breast cancer was also apparent for nonprofessional application of chemical straighteners to another person's hair, where the risk was increased by 27%, researchers add.
Again, this risk did not vary by ethnicity and was seen in both black and non-Hispanic white women.
Somewhat surprisingly, there was a 30% higher relative risk of premenopausal breast cancer associated with light dye use; however, the nonprofessional application of both semi-permanent dyes and straighteners to others at slightly over 30% with both uses was most evident for postmenopausal breast cancer.
Importantly, adjusting for alcohol and hormone replacement therapy (along with the exclusion of women who had ever worked in a hair salon) did not materially change results, the investigators point out. There was also no evidence that body mass index affected study results, the researchers add.
As the authors note, in the early 2000s, Brazilian Keratin Treatments, which contain formaldehyde or one of its derivatives that reacts with keratin when heated, were introduced to global markets.
Formaldehyde is a known carcinogen, the authors point out, and findings from the current analysis of the Sister Study are the first reported estimate of the potential association between straightener use and breast cancer risk after this formaldehyde-containing product was introduced to US markets.
"We were not able to evaluate the formulation of the hair dyes or straighteners assessed, nor are they reliably documented on labels, which is a limitation," the authors acknowledge.
"But these findings…provide evidence to support the relationship of hair dye and straightener use with breast cancer risk and highlight potential differences in associations by ethnicity. As hair dye and straighteners are common exposures, these findings have the potential for substantial public health impact," they argue.
Calls for More Study
Mount Sinai's Bernik also suggested that if a woman is already at high risk for breast cancer — as women in this study were — they might want to use caution when dying their hair permanently at home and seek a better alternative, such as a salon treatment with semi-permanent dye.
"But more definitive studies would need to be carried out before doctors would recommend against permanent hair color," Bernik said.
Coinvestigator Dale Sandler, PhD, chief of the epidemiology branch of the National Institute of Environmental Health Sciences, seconded the notion that these results need to be replicated in other studies.
She also agreed that physicians should use common sense before telling women to stop dyeing or straightening their hair.
"We are exposed to many things that could potentially contribute to breast cancer and it is unlikely that any single factor explains a woman's risk," Sandler said in a statement.
"While it is too early to make a firm recommendation, avoiding these chemicals might be one more thing women can do to reduce their risk of breast cancer," she added.
The study was supported by the Intramural Research Program of the NIH, National Institute of Environmental Health Sciences. White, Sandler and Bernik have disclosed no relevant financial relationships.
Int J Cancer. Published online December 3, 2019. Abstract
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Cite this: Hair Dyes Linked to Elevated Breast Cancer Risk - Medscape - Dec 05, 2019.