Key points from article :
Permanent hair dyes and chemical straighteners linked to an increased risk of breast cancer.
Nine per cent increased risk of breast cancer, this risk is 45 per cent in African American women.
Risk is not associated with semi-permanent or temporary hair dye.
Can't make firm recommendations using these results, but it's better to avoid permanent hair dye.
Analysed data from 46,709 women enrolled in the Sister Study ranging in age from 35 to 74.
Research by National Institute of Environmental Health Sciences and NIH, published in International Journal of Cancer.