What can II use on blister lips or rash due to alergic reaction?

Depends... On cause of blister. If it's a cold sore (herpes) otc zilactin or some topical rx medication can be used. If it's truly allergic you can try a small amount of otc topical Hydrocortisone (don't swallow it), however the source of the allergy should be hunted. If you're having any shortness of breath, tongue swelling or difficulty swallowing you should go to the er now.