Red spots on the arm may be symptoms of cherry angioma, spider nevus, or allergic purpura, and require prompt medical attention to clarify the cause. 1. Cherry angioma: related to the decline of skin function, caused by abnormal proliferation of capillaries, mostly seen in middle-aged and old people. 2. Spider nevus: it is related to high estrogen level in the body, and it is common in pregnant women, and it can also be seen in patients with severe liver disease, such as cirrhosis and liver cancer, which is caused by the low inactivation function of the liver to estrogen. 3. Henochromic purpura: It is caused by the perverse reaction of the small blood vessels of the whole body, and it is related to infection, allergy and other factors. Henochromic purpura is mostly found in the lower limbs, and in serious cases, it can spread all over the body. The specific need to go to the hospital, clear diagnosis and follow the doctor’s instructions to use medication.