I have an allergy rash from hair dye. I have been taking Benadryl (diphenhydramine) for a few days and it has still not completely gone away. What should I do?

Rash too? If scalp is red and itchy as part of the dye reaction, you may need application of topical steroid solution, or oral steroids, to calm down the reaction . These are prescriptions available through your primary doctor, or a dermatologist.