Scientists have called for more research into hair dyes and perming products to assess whether they contain a harmful substance which has been linked to causing cancer.
The comments come after researchers found that hairdressers had a high concentration of a type of carcinogenic chemical in their blood.
Toluidines are supposed to be banned from EU products, but the Swedish study found that hairdressers who apply light-colour permanent dyes or perform perms on their clients seem to be exposed to certain types of the compounds.
The paper, published in the journal Occupational and Environmental Medicine, examined blood samples from 295 female hairdressers, 32 users of hair dyes and 60 controls.
They found that concentrations of ortho-toluidine and meta-toluidine increased significantly with the weekly number of hair waving and permanent hair dyeing treatments.