New research featuring over 46,000 women in the U.S. has revealed potentially worrying links between the use of certain hair products and the risk of developing breast cancer.
The study, published yesterday in the International Journal of Cancer, suggests that women who use products such as permanent hair dyes and chemical straighteners could be increasing their risk of breast cancer by up to 60%.
“Researchers have been studying the possible link between hair dye and cancer for a long time, but results have been inconsistent,” said Alexandra White, Ph.D., head of the National Institute of Environmental Health Sciences Environment and Cancer Epidemiology Group and senior author of the study.
As well as warning of an overall increase in risk of breast cancer for women who use these hair products, the paper reports huge differences in the risks posed by various products to black women and white women.
For white women dying their hair regularly the risk of developing breast cancer seemed to increase by 7%, but for black women, this was far higher at 45%. For ‘heavy’ usage of hair dye, defined as at least once every 5-8 weeks, the increased risk was 8% for white women and 60% for black women.
“In our study, we see a higher breast cancer risk associated with hair dye use, and the effect is stronger in African American women, particularly those who are frequent users,” said White.
The incidence of breast cancer in black women is slightly lower than in white women, but black women are likely to be diagnosed at a later stage of disease than white women and are far less likely to survive their cancer.
The new study is correlative and does not describe a direct cause-and-effect relationship between hair products and breast cancer risk, but considering some of the components of these products have been described to be potential carcinogens or chemicals that can interfere with hormones such as estrogen, there is reason to believe the conclusions of the study.
“The associations seen certainly could be causal, especially since there are known carcinogens contained in many of these products,” said Dr. Anne McTiernan, M.D., Ph.D., an epidemiologist in the Public Health Sciences Division at Fred Hutchinson Cancer Research Center in Seattle. “One thing that surprised me was that the effects of hair dyes and straighteners were seen in both black and white women. Often, studies don’t have enough numbers of women from diverse race and ethnic groups in order to do that,” she added.
“Obviously this topic is useful to look at,” said Dr Larry Norton, medical oncologist and medical director, Evelyn H. Lauder Breast Center at Memorial Sloan Kettering Cancer Center in New York. “Does this work merit further study? Yes, absolutely. Does this prove hair straighteners and hair dyes cause breast cancer? No. There’s a weak association but this association does not equal causation,” he added.
The research looked at women between the ages of 35 and 74 recruited between 2003 and 2009, who had no personal history of breast cancer, but had a sister diagnosed with the disease. The women regularly answered questions about their overall health and lifestyle, including their use of hair products over a period of just over eight years on average.
When they enrolled in the study, 55% of women reported using permanent hair dyes in the year prior to enrolling. During the study, 2,794 women developed breast cancer, with the research finding that permanent (but not semi-permanent or temporary) dyes increased the risk of developing breast cancer.
“One limitation is that the researchers only asked about exposures in the 12 months before the women entered the study,” said McTiernan, explaining that women who had used the products in the past but stopped would be considered non-users, as would those who began after entering the study. “What this does to the data analysis is to underestimate the effect. In other words, the effects of these products on breast cancer risk could very well be larger,” she added.
Worryingly, the study also cited previous research suggesting that these chemicals, which can interfere with estrogen, may be found in higher levels in products targeted to black women.
“The risk associated with permanent dye was small for white women (<10%), but for Black women was much higher (45%), suggesting the type or amount of dye used or application method varies substantially and influences risk,” said White, summarizing the findings on Twitter.
The study also looked at chemical straightening products and found that the risk was increased by 30% for all women, irrespective of race, contradicting a study featuring a similar number of women from 2007, which found no increased risk of breast cancer from these products.
“We saw no higher risk for semi-permanent or temporary dyes. For straightener use, we saw a 30% higher risk in both Black and white women BUT Black women are way more likely to use these products,” said White on Twitter, noting that previous studies on hair dye have largely been in white women.
This is not the first time recently where the safety of beauty products has been called into question. This week, research described the presence of potentially dangerous microbes in common makeup items and earlier this year, the levels of some cancer-causing chemicals in nail salons were found to be higher than in auto garages, potentially putting workers at risk.
“It’s critical, in my opinion, that the FDA be given the ability to regulate cosmetic products because we know that they are absorbed, and if there are carcinogens in them, they can be harmful. If women are worried about their breast cancer risk, this [hair dyes and chemical straighteners] may be one exposure they could avoid. However, hair is very important to many women,” said McTiernan.
So what can be done to further investigate the relationship between breast cancer risk and the use of these hair products?
“It would be reasonable to look at the chemicals involved and put them through more assays to see if there’s any hints of carcinogenicity. Usually in these situations – there would have to be a combination of lab studies to show a potential mechanism and corroborating studies with other populations of people. It is reasonable to do these studies to evaluate the risk further,” said Norton.
Should women who use these products change anything in light of this new work?
“Should a person stop dying their hair? Everything in life has cost and benefit, there’s always risk in everything you do, it depends how important this activity is for you. I wouldn’t tell someone not to use these products, this study doesn’t give anywhere near enough evidence to prove the products in this products are cancer-causing,” said Norton.
This piece was edited at 4.20pm ET on 4th December to add in comments from Dr Norton.