However, when taking into account the risk associated with using chemical hair straightening the products, the gap narrowed.
There was little to no increase in breast cancer risk among women who used semi-permanent or temporary hair dyes, however.
The study, published to the International Journal of Cancer, used data from 46,079 women and found that those who regularly used permanent hair dye in the year prior to enrolling in the study were 9pc more likely to develop breast cancer than women who didn't.
Another finding of the study focused on the link between chemical hair straighteners and cancer.
Scientists at the National Institutes of Health found that women who use permanent hair dye and chemical hair straighteners have a higher risk of developing breast cancer than women who don't use these products. Among this group, the use of permanent dyes every five to eight weeks (or more frequently) resulted in a 60 percent increase in breast cancer risk compared to the 8 percent increase among white women.
The research was conducted by the National Institute of Environmental Health Sciences.
Each woman in the study had a sister with breast cancer, making them part of a high-risk population, which makes the results of the study hard to extrapolate across the general population, according to Ashton.
Well, breast cancer is rarely caused by one thing only. Most notably, vigorous exercise like running and bicycling may reduce your breast cancer risk.
The U.S. Federal Drug Administration (FDA), the agency that oversees the regulation of hair dyes, says on its website it does not "have reliable evidence showing a link between cancer and coal-tar hair dyes on the market today". She pointed out that the Sisters Study's population isn't representative of women as a whole. White and colleagues found that women who used hair straighteners at least every five to eight weeks were about 30% more likely to develop breast cancer.
A United States study has linked frequent permanent hair dye use with a greater risk of breast cancer - but with an important caveat. Many women interviewed in the study might also not accurately recall frequency of use, or whether they used permanent or semi-permanent dyes, Cassell reasoned.
Anne McTiernan, MD, PhD, one of the report's lead authors and a cancer prevention researcher at the Fred Hutchinson Cancer Research Center in Seattle, notes that while being physically active, keeping a healthy weight, and reducing alcohol intake will help you lower your breast cancer risk, you can't control your genes, and you may still get diagnosed with breast cancer even if you run marathons and eat buckets of spinach and kale.
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