A new study claim that women of African ancestry are at much higher risk of cancer if they use permanent hair dyes. Researchers looked at almost 47,000 American women over a period of eight years and found that using permanent hair dye, increases their risk of breast cancer by 45%. There is only a 7% risk, they say, for Caucasian women.

The study has been published in the International Journal of Cancer. It says that the more frequently women coloured their hair, the greater the risk was, with black women who used permanent dyes at least every five to eight weeks seeing a rise of 60%.

The reason behind the difference remains uncertain, however some researchers believe that the way the dye is applied, makes the difference.

The study also found using hair straighteners at least every five to eight weeks increased the risk of breast cancer by 31%, regardless of race. About 74% of African American women reported using chemical straighteners as compared to 3% of Caucasian women.