Red rashes from skin allergies all over the body may be caused by allergic purpura, urticaria, contact dermatitis and other diseases. 1. allergic purpura: the cause of this disease is pathogenic microbial infection, heredity, vaccination, insect bites, pollen, animal dander, etc. Typical symptoms are the presence of purplish-red papules on the face, upper limbs, trunk, suppression of non-fading, so the whole body skin allergy with red rash may be due to allergic purpura. 2. Urticaria: The allergens of this disease are fish, shrimp, eggs, peanuts, mangoes and other foods, as well as dust mites, chemicals, dust and other exogenous substances, as well as physical factors such as sunlight exposure and friction. The occurrence of urticaria may also be related to mental and pathogenic microbial infections. The main manifestation is red or pale white rashes or wind clouds all over the body, which may be accompanied by itching. 3. Contact dermatitis: Studies have shown that exogenous substances that can cause this disease include detergents, leather, clothing materials, insect poisonous hair, adhesive tape, etc. Erythema, papules, edema, blisters and other symptoms will appear at the site of contact, which can be manifested as a generalized skin allergy with a red rash. It is recommended that patients with generalized skin allergy with red rash go to the hospital, complete the relevant examination to clarify the cause of the disease.