The rise in prevalence of contact allergy to methylisothiazolinone in the British Isles.

Since 2005, in the EU, the use of methylisothiazolinone (MI) as a single-agent preservative has been permitted in both leave-on and rinse-off cosmetic products at concentrations of up to 100 ppm. Like others, we have observed a recent large increase in the number of patients with contact allergy to MI. Fourteen dermatology centres from across the British Isles (10 in England, one in Scotland, two in Wales, and one in Ireland) provided their patch test data on MI and methylchloroisothiazolinone (MCI)/MI contact allergy. Nine centres contributed data on both MI and MCI/MI, two centres [number 4 (Cork) and number 14 (Canterbury)] contributed data on MCI/MI alone, and three centres [number 12 (St John’s, London), number 13 (St Mary’s, London), and number 8 (Manchester)] contributed data on MI alone. In 2010, five centres were testing with MI. This number increased over the study period to 12 centres. Analysis was performed on data from January 2010 to June 2013. In all centres, test agents were applied in Finn Chambers® according to International Contact Dermatitis Research Group guidelines. Readings were performed on D2 and D4. Of the 11 centres contributing data on MCI/MI, nine centres tested with MCI/MI 0.02% aq. (Chemotechnique