I’ve never been a fan of these, especially not in products for direct contact with humans & animals, and was saying so for over two decades now.
The main issue of such allergens and not just isothiazolinones is not their chemistry but that they’re often excessively used in many different products of everyday life such as washing detergents (dishes, clothes, cars, you name it), paints, lacquer, glue, fertilisers, pesticides & other agrochemicals, all kinds of industrial liquids down to the stuff used to build our houses, colour our clothes, or clean machines which process our food. I don’t have actual numbers for MIT & CMI but these are produced in many million metric tons per year (guess who sells a metric ton as MOQ?). MIT, CMI and other isothiazolinones are present in nearly everything (literally nearly everything!) which contains water at some point in its production process and isn’t meant for consumption such as paper and in a lot (= estimations talk of ~50%!) of materials potentially degraded by microbes such as fillings and insulation materials. It is virtually impossible to live in a halfway modern world without getting in constant contact with these chemicals and that’s the main issue. No, not just for these two but for nearly every similar product and we will see exactly the same shit going down with ‘modern’, ‘better’, and more ‘natural’ preservatives (as of now, my bet is on caprylhydroxamic acid when it comes to cosmetics).
At least, isothiazolinones have been regulated in cosmetics and allergy prevalence is going down slowly since that day. But, as said ‘same shit, new name’ is so far all humanity managed to produce in too many fields of our lives. We need to rethink the basics and not just find ways around legislations because we can cheat customers and dupe politicians but we can’t cheat nature and we can’t dupe biology.