There are SO many sensitizing ingredients they use ... and since sensitivity develops from exposure, it's common for people to be sensitive to several of the common ingredients.

I'd start with products you know *don't* sensitize you and compare the ingredient lists to products you want to try. Try to buy something with as few potential culprits as possible before adding in the next one. Maybe you have a friend with less-sensitive skin that you could give your unused product to ... I've thrown away so much moisturizer over the years.