Scientists at Brigham and Women’s Hospital and Harvard Medical School used data from nearly 120,000 participants in the Nurses’ Health Study cohort, which is one of the largest investigations into the risk factors for major chronic diseases in women. The participants were followed for 36 years; none had cancer at the beginning of the study.
According to the researchers, women whose natural hair color was blond or light brown were more likely to use permanent hair dyes than were women whose hair wsa dark brown, black or red. Ever users also were more likely to be smokers and consumed more alcohol than those reporting no history of personal permanent hair dye use.
“We explored the association between personal use of permanent hair dyes and cancer mortality. Multivariable analyses showed no significant association between status, duration, frequency, or cumulative dose and cancer related death, and stratified by natural hair color,” the researchers wrote in their study, which was published Wednesday in the British Medical Journal.
Specifically, the study found the use of hair dye did not increase risk of cancers of the bladder, brain, colon, kidney, lung, blood and immune system, or most cancers of the skin or breast.
“The headline result is that overall there is no difference in the rate of cancer in general in women who have used hair dyes and those that have not,” said Paul Pharoah, professor of cancer epidemiology at the University of Cambridge. He was not involved in the study.
Researchers did find a higher risk of the basal cell carcinoma of the skin in women with light hair. Women with darker hair had an increased risk of Hodgkin’s lymphoma.
Pharoah said that part of the study could be misleading, because it could be interpreted to mean that permanent hair dye causes an increase in risk. Because this is an observational study, however, causality cannot be assumed.
“For the cancers where an increase in risk is reported the results are not compelling,” Pharoah continued. “The reported associations are very weak and given the number of associations reported in this manuscript they are very likely to be chance findings. Even if they were real findings the associations may not be cause-and-effect and even if they were causal associations the magnitude of the effects are so small that any risk would be trivial.
“In short, none of the findings reported in this manuscript suggest that women who use hair dye are putting themselves at increased risk of cancer.”