A new study in Occupational & Environmental Medicine has linked frequency of dye and perm use to raised levels of carcinogens found in hairdressers' blood.
Previous studies have found that hairdressers have an excess risk for bladder cancer. Researchers believe this excess risk comes from exposure to carcinogenic aromatic amines in some hair dyes, which have also been linked to increased risk for non-Hodgkin lymphoma and leukemia.
These carcinogens were present in 89% of commercial hair dyes during the 1970s but were subsequently phased out as restrictions on hair dye formulas were introduced.
However, studies in the US and Turkey screening for these banned substances in commercial hair dye products still report levels of carcinogenic aromatic amines.
In the new study, researchers from the Division of Occupational and Environmental Medicine in Lund, Sweden, wanted to measure long-term exposure to known and suspected carcinogenic aromatic amines among hairdressers.
To do this, they assessed blood samples from 295 female hairdressers, 32 regular users of hair dyes and 60 people who had not used hair dyes in the past year. The researchers also gathered data on the participants' other jobs, hobbies and lifestyle that could have influenced the results.
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.
Carcinogenic toluidines found in hairdressers' blood
Overall, levels of aromatic amines did not differ significantly between the three groups. However, in the hairdressers, their weekly levels of aromatic amines called o- and m-toluidines were shown to correspond with the number of permanent light hair color treatments they applied to clients. Toluidines are known to be carcinogenic.
Higher concentrations of o-toluidines were also associated with use of a hair-waving product, a finding that the researchers describe as "somewhat unexpected."
The researchers note the findings of a recent study that found o-toluidines to be responsible for an increase in bladder cancer among workers at a chemical manufacturing plant.
Hairdressers' weekly levels of carcinogenic aromatic amines were shown to correspond with the number of permanent light hair color treatments they applied to clients.
Given their study's findings, the authors suggest that ingredients of hair dyes and perming products should be analyzed to see if these products continue to expose the public to carcinogens.
A Turkish study that undertook a similar task analyzed 54 permanent hair dyes and found that concentrations of o-toluidine could be up to 100 times stronger in dark-yellow permanent hair dye and up to 500 times stronger in black hair dyes.
"This indicates that there is a high variation between products and further supports our ﬁndings that high o-toluidine adduct concentrations may originate from speciﬁc products," write the authors behind the new study.
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.
In 2011, Medical News Today reported on a study by researchers from the National Allergy Research Centre at Copenhagen University in Denmark. They found that people with allergies to substances such as hair dye and latex rubber may have an immune system that can be triggered into defending against some types of cancer.