Prevalence of sensitization to methylisothiazolinone in an italian skin allergy unit

An alarming increase in the prevalence of sensitization to the preservative methylisothiazolinone (MI), alone or in combination with methylchloroisothiazolinone (MCI), has recently been reported, mainly in Northern Europe. Prevalence data from Southern Europe are scanty. We evaluated the prevalence of contact allergy to MI and MCI/MI among 1392 patients consecutively patch tested in 2012 - 2013 at the Clinica Dermatologica of San Martino Hospital, Genoa, Italy. The patients were patch tested with 2000 ppm MI aq. in addition to the Italian baseline series. The MOAHLFA index was registered for all patients. Relevant exposures to MI and/or MI/MCI were determined and the patients' clinical outcome after isothiazolinones avoidance was evaluated. The prevalence of sensitization to MI showed a steep increase of prevalence from 2.3% in 2012 to 6.9% in 2013 while sensitization to MI/MCI rose from 6.76% in 2012 to 9.04% in 2013. Hand and face dermatitis were significantly prevalent in MI allergic patients. Cosmetics, followed by household products, were the most common sources of relevant exposure to both MI and MI/MCI. Clinical improvement after avoidance of isothiazolinones containing products was reported by 85.3% of followed up patients.