Red spots on the back of the hands may be caused by diseases such as insect bite dermatitis, sweating herpes, and allergic purpura. 1. Insect bite dermatitis: the occurrence of this disease is mainly related to the secretion injected into the skin after insect bites, which is the allergen of insect bite dermatitis, commonly found in mites, bedbugs, mosquitoes, fleas and so on. The site of the bite will appear erythema, edema, itching and other symptoms, so red spots on the back of the hand may be insect bite dermatitis. 2. Sweat herpes: the cause of this disease is not clear, may be related to allergies, ultraviolet radiation, dermatophyte infection, intravenous immunoglobulin, mental stress and other reasons. Sweat herpes is mainly manifested by the presence of itchy blisters on the hands or feet, usually starting with red spots, accompanied by symptoms such as tingling or burning sensation. 3. Anaphylactic purpura: Studies have shown that the causes of this disease include pathogenic microbial infections as well as antibiotics, antipyretic and analgesic drugs. Its typical symptom is skin purpura, which can be manifested as red spots on the back of the hands, and can also occur on the face, trunk, buttocks and other places. To summarize, there are more reasons for patients to have red spots on the back of the hands, and they need to go to the hospital for consultation to clarify the specific cause of the disease.