My motherinlaw is allergic to Bactrim Sulfa drugs. They have her zinc sulfate and she broke out in rash. I thought sulfate was different. Why rash?

New allergy. You are correct that there is not a relationship between sulfa and sulfate, but some patients can develop an allergy to other things, or the rash is unrelated to the zinc sulfate. Rashes really need to be seen to be accurately diagnosed.