Women who use permanent hair dye or chemical straighteners might have an elevated risk of developing breast cancer, national health researchers said in a study published Wednesday.
Scientists found that women overall who used permanent hair dye had a 9% higher risk of breast cancer, while black women had a 45% increased risk. An 18% higher risk was seen among women who used chemical straighteners.
The study, conducted by researchers from the National Institutes of Health and the University of North Carolina-Chapel Hill, was published this week in the International Journal of Cancer.
“Our findings do suggest that women should consider their use of hair products in light of the fact that the chemicals in hair dye and chemical straighteners may influence their risk of developing breast cancer,” said Dr. Alexandra White, one of the study’s researchers and head of the National Institutes of Health’s environment and cancer epidemiology group. “The overall risk is not large and chemical hair products are just one of many factors that may influence a woman’s chances of getting breast cancer.”
She added that since semi-permanent dyes were not associated with breast cancer risk in this study, women could consider switching to these hair products.
The study included data from 46,709 women in the U.S. and Puerto Rico who were part of the Sister Study — women who had no history of breast cancer but had at least one sister diagnosed with breast cancer.
Research into the link between hair dye use and breast cancer risk has been inconsistent, with some studies reporting a positive association while others concluding there is no higher risk.
Recent case control studies have reported a 25% increased risk between hair dye and breast and bladder cancer.
Personal hair product use varies depending on ethnicity. The researchers noted that, for example, black women mostly tend to use straighteners.
“Thus differences in exposure to chemicals through hair products may contribute in part to racial disparities in breast cancer incidence,” the study says.
It is estimated that more than one-third of women over the age of 18 in the U.S. use hair dye.
Hair products contain more than 5,000 chemicals, including additives that can reach breast tissue and disrupt the body’s endocrine system, which includes glands that secrete hormones directly into the blood, the study’s researchers report.
There are many different formulas for hair dye and straighteners, which have evolved over time, making it difficult to pin down which ingredients might contribute to an increased risk of breast cancer. The study did not ask participants about specific products they used, and the researchers were unable to analyze individual compounds found in these hair products.
Treatments that permanently or semi-permanently straighten hair contain a wide range of chemicals, some of them known carcinogens such as formaldehyde.
The National Toxicology Program has labeled some of the chemicals that are currently or were previously used in hair dyes as “reasonably anticipated to be human carcinogens.”
According to the American Cancer Society, the International Agency for Research on Cancer does not consider personal hair dye use as “classifiable as to its carcinogenicity to humans,” but has recognized that workplace exposure as a hairdresser or barber is “probably carcinogenic to humans” based on data regarding bladder cancer.
The Food and Drug Administration regulates the safety of cosmetics, including hair dyes, but does not approve each ingredient used in the products before they hit the market, leaving manufacturers responsible for the safety of their products.
Although the study’s researchers observed a positive association between chemical hair dyes and straighteners and breast cancer, they stressed that their findings should not be interpreted as cause and effect.
“We would like to reiterate that the overall risk is not large and chemical hair products are just one of many factors that may influence a woman’s chances of getting breast cancer,” Dr. White said.