Recent research published in Occupational & Environmental Medicine carried out by Swedish scientists has again highlighted the exposure of hairdressers to potentially hazardous chemicals, this time of carcinogenic and sensitising toluidines in hair dyes and hair-waving (‘perming’) products.
This is just the latest in a long line of news stories about chemicals in personal care products – including methylisothiazolinone in suncream, triclosan in antibacterial products, and phthalates in nail polish,
The latest research, led by Gabriella Johansson at Skåne University Hospital in Lund, Sweden, has been picked up by a number of outlets, including Reuters, ChemicalWatch, SpectroscopyNOW, Medical Xpress, Nature World News and MedicalResearch.com. What the researchers found was that m-toluidine was present above the limit of detection in the blood of >97% of a cohort of hairdressers, personal dye users and controls (a total of 387 people), with the figure for o-toluidine being ~50%. The chemicals were detected indirectly by GC–MS analysis of their adducts with haemoglobin, which is a good way of assessing average exposure because of haemoglobin’s relatively long lifetime.
This of course isn’t the first time that chemicals originating from hair dyes have raised alarm bells – p-phenylenediamine gained attention in late 2011 following a death from a suspected allergic reaction. The issue this time is that toluidines, unlike p-phenylenediamine, were banned from cosmetics in the EU in the late 1970s (as stipulated on page 18 of the original 1976 EU directive), so it is a surprise to find them in the blood at all.
Two facts uncovered in Johansson’s study seem to suggest that these haircare products are the source of the toluidines. Firstly, they found that o-toluidine concentrations increased with the number of hair-waving treatments, and that m-toluidine increased with the number of hair-dyeing treatments. Secondly, and more tellingly perhaps, they analysed a commerical (multi-component) hair-waving product and found both o-toluidine (up to 0.23 ng/g) and m-toluidine (0.15 ng/g).
However, the matter is not as clear-cut as it might seem, because, as the authors say “We evaluated the exposure … [for] hairdressers, consumers and controls, and found no overall significant difference.” Likewise, research last year led by Marie Thi Dao Tran at Copenhagen University Hospital found that “the prevalence and the severity of fragrance-related symptoms [of chemical intolerance] were similar in hairdressers and the general population”.
Such research points to a complex picture, with possibly multiple routes of exposure subject to factors not accounted for in the current study. Clearly, there is a need to devote more attention to where the compounds are coming from, as the authors themselves suggest: “A study measuring both exposure to aromatic amines and product analysis … would strengthen the conclusions about hairdressers’ exposure to carcinogenic aromatic amines, and is encouraged”.
Indeed, such analysis should really go hand-in-hand in this sort of study, and is essential in order to draw any meaningful conclusions from the work. Analysing all the haircare products used by several hundred people is not going to be a small task, but perhaps is illustrative of the amount of effort that needs to be made to link cause and effect in such a complex area.
The good news is that this sort of analysis – once a highly labour-intensive endeavour – is becoming increasingly quick and straightforward, because of advances in sample preparation and automation. Advanced analytical techniques like GC×GC–TOF MS are also playing their part, by making it possible to get reliable, quantitative information out of such highly complex samples – as we’ve illustrated ourselves in Application Note 522 for the case of allergens in cosmetics.
David Barden received his Ph.D. in Organic Chemistry from Cambridge University in 2004, and during his time as an editor at the RSC wrote news pieces for Chemistry World on various scientific topics. He is now Technical Copywriter at Markes International, where he draws on the expertise of his colleagues to explain how new thermal desorption and mass spectrometry technologies can be applied to analyse volatile organic compounds in a wide variety of situations.