Namely
Methylisothiazolinone, better known by the acronym MIT, is used as a synthetic preservative in cosmetics. It has been used as a substitute for parabens in so-called "paraben free" products by a number of brands. But, it turns out that the molecule is extremely allergenic, it's nerd! The American Contact Dermatitis Society even designated it in 2013 as the "ALLERGEN OF THE YEAR"!
Due to many cases, European legislation has recently adapted:
The ingredient has been completely banned in rinsed products since February 2017 and since April 2018, the maximum permitted levels of MIT in rinsed products have been largely revised downward (see below).
MIT is mostly used with CMIT (Methylchloroisothiazolinone).