The new study in Occupational & Environmental Medicine reveals a team of researchers led by Gabriella Johansson to have measured levels of eight potentially carcinogenic chemicals in the blood of 295 hairdressers, 32 regular users of hair dyes and another 60 who had not used hair treatments for over a year.
The authors decided to use a much greater number of hairdressers than other groups because they wanted to study dose-response associations, which requires a large sample group.
Samples were analysed with gas chromatography–tandem mass spectrometry where levels of haemoglobin adducts were firstly determined in blood to provide a long-term exposure estimate.
According to Johansson, although levels varied considerably, these concentrations were generally similar in all three groups of participants.
o- and m-toluidines
The team went on to discover levels of o- and m-toluidines rose for hairdressers, depending on the number of weekly permanent light hair colour treatments and perms that they recorded.
These chemicals are banned in cosmetic products in Europe. However, studies in the US and Turkey screening for these banned substances in commercial hair dye products still report levels of carcinogenic aromatic amines.
"Hairdressers who use light-colour permanent hair dyes, other permanent hair dyes and hair waving treatments seem to be exposed to o- and m-toluidine as indicated by associations with the number of treatments performed," say the authors.
"Analyses of hair waving and hair dye products should be performed to identify the possible sources of exposure to o- and m-toluidine," they add.
The researchers also recommend that hairdressers should minimize exposure risk by wearing gloves and by doing any tasks that cannot be performed wearing gloves - such as cutting hair - before any dyes or perms are applied
Hair dye safety issues
Over the years, concerns that some hair-dye chemicals may increase the risk of bladder cancer in hairdressers has led to a phasing out of classified carcinogenic aromatic amine chemicals.
However, when the team analysed a perming treatment, randomly purchased in Sweden, they found it to contain o- and m-toluidines.
“Future studies should focus on finding exposure sources of o- and m-toluidine in products used by hairdressers," they concluded.