Contact allergy caused by methylisothiazolinone: the Belgian-French experienceThe chemical Kathon CG ® , a mixture of the preservatives methylchloroisothiazolinone (MCI) and methylisothiazolinone (MI), was the leading cause of a worldwide epidemic of contact-allergic reactions in the eighties. From 2000 on, MI alone became allowed in industrial products and in 2005 authorities gave a green light for its use in leave-on and rinse-off cosmetics up to a maximum concentration of 100 ppm (0.01%). Following initial occupational cases, a continuously increasing number of consumers sensitized to MI have been reported and both Belgian and French allergy groups decided to routinely test MI in their baseline series from 2010 onwards. Two multicenter studies, comprising 8,680 and 7,874 patients in Belgium and France respectively, both clearly show the rise in contact allergy caused by MI, with a spectacular sensitization rate of ∼ 6.0% in 2012, even increasing to 7.0% in 2013. Mostly middle-aged women, presenting with facial-and/or hand dermatitis, were affected, although very young children were reported as well. Furthermore, the data confirmed that sensitization is primarily caused by cosmetics (mostly leave-on, but also rinse-off), household detergents and water-based paint. This unprecedented outbreak of contact sensitization to a preservative agent in Europe, and beyond, should have alerted the authorities much sooner and meanwhile the need for safer use concentrations of MI in cosmetics, detergents and industrial products is becoming more urgent every day.