Contact dermatitis refers to an acute inflammation occurring in the region of the skin and mucous membrane after contacting some substances and is divided into allergic contact dermatitis and primary irritable contact dermatitis. The pathogenesis of allergic contact dermatitis belongs to type IV delayed allergy. The contact substances are not irritable, but a few people can be allergic.After contacting this substance again, dermatitis can happen in the contact region and nearby region 12-48 hours later. The contact substances to cause primary irritable contact dermatitis are strong irritable, such as strong acid and strong base, etc. Dermatitis can happen in any person after contact. "Paint Boil" and "Plaster Boil" explained in Chinese medicine belong to the category of this disease.