Common causes of sudden red nevus on hands include hemangioma, spider nevus, and anaphylactic purpura. 1. Cherry hemangioma: it is the most common hemangioma, the etiology of which is still unclear, and it increases with age, manifesting as round red papules, soft in texture and higher than the skin surface. 2. Spider nevus: this disease may be related to the increase of estrogen level, commonly found in acute hepatitis, chronic hepatitis, cirrhosis and other diseases, as well as healthy pregnant women. It manifests as a red nevus with radial capillaries around it and spider-like appearance and other symptoms. 3. Allergic purpura: the cause and pathogenesis of this disease is not clear, may be related to infection, allergy, drugs, genetics and other factors, manifested as a pinpoint to soybean-sized purpura on the skin, can be accompanied by arthralgia, abdominal pain and kidney damage. It is recommended that patients go to the regular hospital in time, follow the doctor’s instructions to clarify the diagnosis and active treatment.