Women who use permanent hair dye and chemical hair straighteners are at a higher risk of developing breast cancer than those who do not use these products, according to a study which analysed data from nearly 47,000 women. The data was collected from participants in the Sister Study, a nationwide effort by the US National Institute of Environmental Health Sciences (NIEHS) to learn how the environment and genes may affect the chances of developing breast cancer. The researchers, including those from the NIEHS, said women who used hair straighteners at least every five to eight weeks were about 30 percent more likely to develop breast cancer. While the association between straightener use and breast cancer was similar in African American and white women, its use was much more common among African American women, they said.