Itchy red spots on the legs may be caused by insect bite dermatitis, allergic purpura, contact dermatitis and other diseases. 1. Insect bite dermatitis: this disease is an allergic skin disease that occurs when the body is bitten by insects, the secretions of insects are allergens, commonly found in bedbugs, mosquitoes, lice, fleas and so on. Prevalent in the limbs extension surface, buttocks and other places, the bite will appear red spots, swelling, blisters, itching and other discomforts, so the patient exists on the legs long red spots very itchy situation. 2. Anaphylactic purpura: the causes of this disease include bacterial infection, viral infection, parasitic infection, heredity, cold stimulation, pollen contact, etc., but also with cephalosporin antibiotics, antipyretic and analgesic medications related to the limbs and buttocks, often in the limbs and buttocks, which can be manifested as red spots on the legs, with or without itchy. 3. Contact dermatitis: the disease is caused by contact with allergens, such as insect hair, pollen, detergents, clothing materials, etc., mainly in contact with the site will appear clear boundaries and accompanied by itchy erythema, so the red spots on the legs itchy may be caused by contact dermatitis. It is recommended that patients with itchy red spots on the legs go to the hospital to clarify the cause of the disease.