Large red erythema on the thighs is considered to have the following possibilities: i. It may be erythema multiforme, which mainly occurs on the thighs, upper limbs, and circumference, and can be seen in mucous membrane areas, such as oral mucosa or vulvar mucosa that can break down, which may be due to infection or allergy, and other factors. For clinical treatment, oral loratadine capsules can be taken once/day, 1 capsule/time. Combined compound glycopyrrolate capsules 3 times/day, 2 capsules/dose. Topical treatment with denuded ointment 1:1 mixed with zinc oxide ointment of boric acid. Second, may consider urticaria, mainly due to infection, or serious medical diseases, such as renal failure, heart failure, or due to allergies and other factors, in the treatment can be oral Avastin capsules, and topical application of Furfuracan lotion for treatment.