After the skin allergy, the most important manifestation on the skin is the appearance of red puffs. External factors cause allergy, resulting in mast cell degranulation and release of histamine, which manifests as puffs. Common allergies are mainly caused by the following: first, food caused by allergies, such as eating fish, shrimp, peanuts, apples, peaches, etc.; second, oral medications caused by allergies, such as eating cephalexin tablets, cotrimoxazole tablets; third, environmental factors caused by allergies, such as environmental humidity, environmental dust is more; fourth, other causes of allergies, such as ultraviolet radiation, the body has pathogenic bacteria infection, sports, etc..