I usually check labels when I buy stuff, but yesterday I quickly chose a shampoo when they didn’t have my usual. Then later I looked at the label. It has methylisothiazolinone. I hadn’t heard of it and googled it. It turns out it is a major allergen and a British study showed 10% of the population has a skin reaction, some serious. Here’s an article about the allergies caused by this chemical: https://www.nytimes.com/2015/01/24/business/allergy-trigger-found-in-many-personal-care-items-comes-under-greater-scrutiny.html?emc=edit_th_20150124&nl=todaysheadlines&nlid=68634180&_r=0
Here’s a youtube BBC segment on it: https://youtu.be/28hyTi56MTo
I also found a website https://www.ewg.org/skindeep/
That lets you search by chemical or product name for cosmetic and skin care products including things like sunscreen, mouthwash, and toothpaste in addition to lotions, shampoos, and makeup.
It rates each product based on all of the individual ingredients and those individual ingredients are evaulated as well. Each chemical compound/ingredient has a list of scientific references to back up what they have said, as well as a list of which countries or regions have banned or restricted a chemical compound’s use in products.