I discovered I was allergic to Methylisothiazolinone about 7 years ago. They replaced parabens (about 3% allergic to it) with Methylisothiazolinone and its brother and sister chloroisothiazolinone and benzoisothiazolinone, which according to reports from the EU have caused an explosion of allergic dermatitis, otherwise known as eczema. It's a preservative. Each individual manufacturer will be testing whether their product is safe in isolation, but nobody is testing whether the onslaught we are subjected to is safe - the chemical is a neurotoxin. It's in spray cleaners, shampoos, conditioners,washing up liquid, washing liquids, clothing conditioners, lotions, paints, you name it - even mouthwashes. The EU has asked manufacturers to remove it from anything "leave on" like creams and moisturisers and sun creams. I'd be surprised if the Purell has any need for preservative, but if it is scented, the scent may have it in, and it's REALLY hard to find out from manufacturers if that's the case if you are sensitive.
It will sometimes be listed as Kanthan on labels. It will sometimes NOT be listed on labels but be included in the scent additive, and that is why some people of my age have suddenly developed eczema having never suffered from it before. I try really hard to keep it out of my home, and to avoid contact with it, but it is ubiquitous outside the home. I don't have such a bad allergy as some people - I generally get eczema on my foot and eyelid (yes! I know! weird...) but some nurses with the allergy have looked like they have gone ten rounds with Mike Tyson, with swollen faces etc, and have had to leave the profession, due to the extent of the contact with this chemical, which is added to floor cleaners and surface cleaners and a lot of other stuff.