As you may guess, if something is only recommended in products that you rinse off (cleansers and shampoos), then it’s probably not the best ingredient for the skin.
Methylisothiazolinone (MI) is a preservative that' super efficient against bacteria at surprisingly low concentrations. The problem with it though is that it can also sensitize and irritate the skin quite easily when it comes in leave-on formulas.
Currently, some countries are considering to ban it entirely (like Denmark) and the permitted use level is very low (under 0.01%). Luckily there are plenty of products on the market with other preservative options so if you are a better safe than sorry type it's probably best to avoid it.