How to get rid of redness on your face from face wash that you're allergic to?

Benadryl (diphenhydramine): Start with Benadryl (diphenhydramine) (oral tablets) but if no better in a few days, see your doctor. Perhaps at that point they might use systemic (oral or injectable) steroids as well, or topical steroids for the face. I usually don't recommend use of otc cortisone cream for this unless you've been seen by a doctor and it was recommended.