A glitch in the production process could have resulted in carcinogenic chemicals getting into dyes and perming products, Swedish scientists warned. Researchers at Lund University found that hairdressers had a high concentration of toluidines -  a dangerous chemical banned the EU in the early 1990s. Scientists involved in the study had fear that toluidines could still be found in modern hair dyes.

They measured the levels of eight carcinogenic compounds, including toluidines, in the blood of 295 female hairdressers, 32 regular users of hair dyes, and 50 people who had not used any dyes or perms for 12 months. It was revealed that for people who regularly came into contact with hair dye or perming products, the levels of toluidines were higher, leaving them at higher risk of bladder cancer.

Dr Gabriella Johansson, from Lund University’s Division of Occupational and Environmental Medicine, in Sweden said: 'There’s still a massive debate on whether there are still carcinogenic compounds present in modern hair dyes. We still really have no idea what’s in some of these products, they’re so complex. But we should call for more research into dying and perming products to find out the cause of increased toluidine levels in the blood of people who regularly come into contact with them.

She also added that 'for hair dyes it’s important to work properly with gloves when you apply the colour and then you apply it to the hair, you have to be so careful. We believe that the main exposure is skin contact.’