A lot of red dots on the arm may be related to cherry angioma, perifollicular keratosis, and allergic purpura. 1. Cherry angioma: also called senile hemangioma, commonly seen in middle-aged and old people. Clinical manifestations of localized spherical or hemispherical bright red papules, the etiology is not yet clear, belonging to the formation of capillary proliferation and expansion of benign vascular proliferative diseases. 2. Perifollicular keratosis: a chronic follicular keratosis skin disease, usually manifested as follicular pimples of the size of a needle tip to a grain of corn. It may be related to autosomal dominant inheritance, vitamin A deficiency, metabolic disorders, etc. It usually has no conscious symptoms. 3. Allergic purpura: related to infection, food, drugs and other factors, manifested as pinpoint to soybean-sized red papules on the extremities, palpable purpura. When the arm appeared small red spots, should go to the hospital as soon as possible, to clarify the cause of the disease, under the guidance of professional doctors for standardized treatment.