Methylisothiazolinone in rinse-off products: additional fuel to the world epidemics of allergic contact dermatitis to isothiazolinones

ORIGINAL ARTICLE, p 115 In 2005 methylisothiazolinone (MI) was allowed in cosmetics as a preservative at the maximum level of 100 ppm (Cosmetic Directive 2005/42/EC). In four to five years several cases of allergic contact dermatitis (ACD) were published, mainly due to wet wipes for personal hygiene, hair and facial cosmetics, deodorants and sunscreens. In a few years a real epidemic of ACD from MI was installed in Europe1 and all over the world. In some contact dermatitis clinics more than 10% of patients tested were allergic to MI, mostly with relevant reactions.2 3 Young children were also frequently affected.2 4 Although there were several alerts from dermatologists and the European Society of Contact Dermatitis,1 the European regulatory authorities that should protect European citizens have not yet agreed on a final decision to prohibit this potent sensitizer in cosmetic products. As leave‐on cosmetics with such high concentrations of MI are known to elicit ACD and, eventually, also sensitize individuals, some in the cosmetic industry have been slowly removing MI from their leave‐on products. Until now, apart from clinical data, there was no proof that rinse‐off products with MI could also elicit ACD and they are still frequently found in the market. The work elegantly developed by Yazar et al.5 produced definitive proof that rinse‐off products containing MI, even at half the maximum accepted level (50 ppm), elicit ACD in MI‐sensitized individuals. Therefore, MI at 50 ppm is not safe and further studies should be done to determine a ‘safe’ level, if any, of MI in rinse‐off cosmetics.