The red rash on both sides of the buttocks is particularly itchy may be due to ringworm, contact dermatitis, urticaria and other diseases. 1. ringworm: the disease is caused by fungal infection, mostly seen in red trichophyton, flocculent epidermolysis bullosa, etc., which can be transmitted through indirect contact or direct contact. It is often triggered by factors such as low immunity and heavy sweating, resulting in red rashes on the buttocks and groin of patients, accompanied by itching. 2. Contact dermatitis: this disease refers to when the skin comes into contact with exogenous allergens, causing irritation to the skin and triggering an allergic reaction, which can be seen in underwear materials, detergents, soaps and so on. The contact area will appear erythema, itching and other symptoms, can be manifested as a red rash on both sides of the buttocks especially itchy. 3. Urticaria: The causes of this disease are complex, such as excessive stress, animal dander, dust mites, mangoes, etc., but also related to viruses, bacteria, fungi, parasitic infections. The typical symptom is that the patient suddenly feels localized itching of the skin, localized red or pale-white masses, so a red rash on both sides of the buttocks is particularly itchy may be hives. It is recommended that patients with a particularly itchy rash on both sides of the buttocks go to the hospital to clarify the specific cause.