Women who regularly use permanent hair dye could be increasing their risk of breast cancer up to 60 percent, according to scientists writing in the International Journal of Cancer.
A study based on the medical records of more than 45,000 women found a positive correlation between permanent hair dye and breast cancer—particularly among those who are black.
While the paper is based on patterns and trends and, as such, doesn't confirm a direct cause, it adds to research suggesting there may be carcinogens lurking in commonly-used beauty products.
"The results do not surprise me," Otis W. Brawley, medical oncologist and epidemiologist at the Hopkins-Kimmel Cancer Center, told Newsweek. "Many of us have worried that the chemicals in especially the permanent hair dyes and hair straighteners have the potential to cause cancer."
Taken as a group women who regularly dyed their hair appeared to be increasing their risk of developing breast cancer by 9 percent. However, for black women, the risk of developing breast cancer was significantly higher—at 45 percent.
This increased even further, to 60 percent, among black women who heavily used hair dye, defined in this case as once (or more) every five to eight weeks. The associated risk for white women, in contrast, was 7 percent for regular use and 8 percent for heavy use.
There also appeared to be differences depending on the type of hair dye used. Dark hair dye was associated with a 51 percent increase in risk for black women and an 8 percent in risk for white women. When it came to light hair dye, there appeared to be a 46 percent increase in risk for black women and a 12 percent increase risk for white women.
Why there are racial variations is unclear, but the researchers suggest it may be linked to differences in the way it is used or differences in the way products marketed for black and white audiences are made. The study's authors reference previous research that suggests those made for black women could have higher levels of endocrine-disrupting chemicals.
"Black women are already at an increased risk of breast cancer, and drawing a clear line to hair products is difficult," Stephanie Bernik, MD, Chief of Breast Surgery at Mount Sinai West in New York told Newsweek.
"Having said that, I do believe the study gives us enough evidence to call for a prospective trial designed to specifically look at this one factor to see if the increased risk of cancer persists. In the meantime, I would caution patients that there is a possible link between hair dyes and cancer, although more research is needed."
They also found a significant correlation between breast cancer risk and chemical hair straighteners, with the researchers emphasizing this needs to be backed up by other research. (Other studies have confirmed no breast cancer risk associated with hair relaxers)
However, in this case, the risk was consistent, increasing across all races by 30 percent for women who use chemical hair straighteners every five to eight weeks or more. Though, as the study authors point out, this is likely to affect black women more as chemical straighteners are used by black women more than they are by white women.
As far as their advice for women who dye or chemically straighten their hair goes, Dale Sandler, Ph.D., chief of the NIEHS Epidemiology Branch who was involved in the research, points to the numerous other carcinogenic chemicals people are regularly exposed to.
Brawley advises women use hair dye and chemical hair straighteners very carefully but says there are other things that will have more of an impact on whether someone will develop cancer or not.
"I would also point out that the combination of obesity, consuming too many calories and lack of physical activity has a much higher relative risk for breast cancer in both black and white women," said Brawley, a former Chief Medical and Scientific Officer of the American Cancer Society.
Michael Jones, Senior Staff Scientist in Epidemiology at The Institute of Cancer Research, said: "It is too early to make a firm recommendation on the basis of one study, and further research is needed. The whole literature needs to be evaluated by expert groups, bringing together the evidence to make recommendations" he told Newsweek. He adds there are limitations to the study.
"The Sisters Study is a good prospective cohort study—but women were recruited to the study because they had a sister with breast cancer, so the conclusions wouldn't necessarily hold true for women in the wider population, hence the need for further confirmation."
There were no observable differences in cancer risk between women who did not die their hair period and those who used temporary or semi-permanent dye.
The research was based on the medical records of more than 46,000 women aged 35 to 74 from the Sister Study, meaning all women involved had a close relative who had died of breast cancer. The results include information from a follow-up period of roughly 8 years, when 2,794 breast cancers were identified.
The article has been updated to include comments from Stephanie Bernik, Chief of Breast Surgery at Mount Sinai West, and Otis W. Brawley, medical oncologist and epidemiologist at the Hopkins-Kimmel Cancer Center.