Methylisothiazolinone (MI) is a preservative used in many household and industrial products. There has been an unprecedented global rise in allergic contact dermatitis (ACD) from its presence in personal care products (PCPs). In 2005 changes to EU legislation allowed MI, used in combination with methylchloroisothiazolinone (MCI), to be used at concentrations of up to 100ppm, 25 times higher than previously permitted. MI was also permitted to be used alone, whereas previously it was only used in combination with MCI in a 3:1 mix.(1) This resulted in the chain of events that led to the current MI allergy epidemic.By 2010, the first case series of ACD to MI as a cosmetic allergen was published. This article is protected by copyright. All rights reserved.