Colourings used in some permanent hair dyes could cause cancer.
The claims are being made by European health officials in Brussels.
They want the hair dye industry to prove the chemicals used in the products are safe.
Semi-permanent dyes safe
The concern centres around dark-coloured permanent dyes used every four to six weeks.
Scientists are not worried about semi-permanent and temporary hair dyes.
The Cancer Research Society is advising people not to use the products until further research has been carried out.
A spokesperson for the Cosmetic Toiletry and Perfumery Association has said hair colourants are among the most thoroughly studied products on the market and they are safe when used properly.
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