Certain adhesives and plasticizers.
Can't use band-aids, so if I get a cut on my finger, for example, I have to wrap it in gauze -- makes the most minor thing look major.
Shoe shopping is hell.
Vinyl has been perfected to look like leather, and if I get vinyl next to my feet they swell up, itch, break out and finally the skin peels off. Takes about 2 weeks for it to clear up. And even if the packaging says something like "all leather uppers" there is often some vinyl components. It's always a treat to see the impatient or stupid expression on the salesclerk's face when I ask about the vinyl.