Can you be allergic to Imuran without being allergic to 6mp?

They start out as different chemicals but after metabolic processing the chemical is identical. Imuran breaks down into 6mp.

It might be important to distinguish side effect, from allergy, form intolerance. All of these can suck, but each has different implications.

A side effect might be managed with dosing, food, or additional drugs. Allergy will involve antigens, might also be managed with something like an antihistamine.

Intolerance means all management options failed.

I see you report Mesalamine intolerant. BE careful about concluding 6mp intolerance too quick, because you can run out of drug options.

Most medication reactions on the skin are everywhere, not localized to just the face... Ask your doctor, and also consider if anything else has changed recently that might also be to blame (new shampoo, moisturizer, or anything else applied to the face).