New research raises concern about the safety of permanent hair dye and chemical hair straighteners, especially among African American women. The study was published Wednesday in the International Journal of Cancer.
Previous research in animals has found links between certain chemicals in hair dye and straighteners and cancer. But findings from other human studies on the association between hair dyes and straighteners and cancer have been inconsistent. This large, prospective study provides firmer evidence of a link.
Researchers analyzed data from an ongoing study called the Sister Study, looking at medical records and lifestyle surveys from 46,709 women between the ages of 35 and 74. Women answered questions about their use of hair dyes and straighteners. While earlier studies on hair dye and cancer risk included mostly white women, the new study includes 9% African American women.
Researchers found that women who used permanent hair dye or chemical straighteners were at higher risk of developing breast cancer.
"The association was notably higher among black women," says epidemiologist Alexandra White, study author and an investigator with the National Institute of Environmental Health Sciences, who studies environmental risk factors for breast cancer.
After eight years of follow-up, White found permanent hair dye use was associated with about a 7% higher risk of developing breast cancer among white women, "whereas in black women that risk was about 45 percent."
That risk was even higher among black women who dyed their hair frequently, every one or two months.
Researchers don't know which ingredients in the products might be of concern. The study did not look at the specific ingredients in the products women were using, only at whether they had used the product and whether they developed breast cancer.
All women in the Sister Study were already at high risk for breast cancer since they had a sister who had breast cancer. This family history put them at increased risk but that does not influence the findings of this analysis since all the women in the study had this same family history, but only some of them used hair dye and straighteners.
Researchers note that in the United States, breast cancer incidence remains high for all women and appears to be increasing for non-Hispanic black women, who also are more likely to be diagnosed with more aggressive forms of the disease and more likely to die from it.
Hair products contain more than 5,000 chemicals, according to researchers, including those with mutagenic and endocrine-disrupting properties such as aromatic amines, which can raise cancer risk, according to White.
When it came to chemical straighteners, risk didn't vary by race. Both black and white women who used hair straighteners were about 30% more likely to develop breast cancer than those who didn't use the products. However, black women are more likely to use them, with about 75% of black women in the study reporting they straighten their hair.
"For the chemical straighteners one of the big concerns there is formaldehyde, which is a known carcinogen," says White. She notes that in the early 2000s just before the study began, Brazilian keratin treatments came on the market. This new treatment, commonly called a Brazilian blowout, contains formaldehyde, while earlier hair straightening treatments did not.
The study findings should be understood in context, says Dr. Otis Brawley, a medical oncologist with Johns Hopkins University. The actual risk found for use of these hair treatments is quite low, he adds, especially compared with other known carcinogens like tobacco or radiation. "This is a very weak signal that these things might be causing cancer in the population," he says.
Much more research is needed, he says, to know for sure how risky these products are. For example, long-term clinical trials with a control group and placebo would be more definitive, but this type of study "would be difficult if not impossible to do."
"Sometimes science just cannot give us the answers that we want it to give us," says Brawley.
In the meantime, Brawley says, there are certain lifestyle factors that have stronger evidence of a link to cancer and are more important for women to focus on. "It is for certain that obesity, consuming too many calories and lack of exercise is a risk factor for breast cancer, a definite risk factor," he says, while the findings of this study only add up to a "perhaps" when it comes to risk.
Dr. Doris Browne, a medical oncologist and former president of the National Medical Association, suggests women start a conversation with their doctor about their risk for breast cancer.
"I think it's important for women, particularly African American women, not to panic every time a study comes out," she says. "But it should raise questions for our primary care providers."
For example, Browne suggests doctors and patients discuss the use of hair products like dyes and straighteners along with other aspects of a "social history" like alcohol consumption, smoking, obesity and living near environmental contaminants.
According to Browne, the key lesson from this study for both doctors and patients is that "when we are aware of a new association (of breast cancer risk) we need to increase our surveillance" to include this potential risk factor in doctor-patient discussions.
For both races, there was no increased risk for women who used semi-permanent or temporary dyes, the kind that eventually wash out with shampooing. To reduce risk, researcher White says women might want to choose these products instead.