Study: Cancer risk and the safety of long-lasting hair dyes discusses cancer risk studies that raise questions about the safety of long-lasting hair dyes. Long-lasting hair dyes are popular, and their safety has been well researched. But new epidemiology studies show their use correlates with increased risk of breast cancer. Most women in developed countries color their hair. Now, after weeks of isolation to tamp down the coronavirus pandemic, those locks may not be looking their best. While many consumers mull the options for at-home treatments, new data from epidemiology studies are raising questions about whether some hair color chemistries may increase the risk of breast cancer. The new studies contrast with decades of toxicology research showing the safety of reactive dye processes used to permanently color hair in salons and at home. Join C&EN to learn how hair color products work and why some experts think they deserve a closer look.

It was not the usual toxicology results but rather findings from two epidemiology studies that have renewed scrutiny of the chemicals in hair color and their potential link to cancer. A December 2019 study by the US National Institute of Environmental Health Sciences found a correlation between the use of permanent hair dye and increased risk of breast cancer (Int. J. Cancer 2019, DOI: 10.1002/ijc.32738).

Llanos looked at data on the use of hair colors and straighteners by Women’s Circle of Health participants. She found that black women who used dark hair dye had a 51% increase in overall breast cancer risk and a 72% increased risk of estrogen receptor–positive (ER+) breast cancer compared with black women in the study who did not color their hair (Carcinogenesis 2017, DOI: 10.1093/carcin/bgx060). These risks were higher for women who used dye more frequently. Women who had salon-applied dyes had a lower risk of breast cancer than those who applied dyes at home.

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