The red spots on the arms are painless and itchy and may be caused by cherry angioma, perifollicular keratosis, purpura and other diseases. 1. Cherry hemangioma: a more common type of hemangioma, mostly seen in the elderly, that is, in the arm, trunk and other parts of the diameter of a small red papule, pressure can fade, but there is no obvious performance, often painless and itchy. 2. Keratosis pilaris: it is a kind of dominant hereditary skin disease, the most common parts are face, neck and outer side of the arms, etc. The main features are pinpoint size and firmness. The main feature is the pinpoint size and hard papules, the color can be the same as normal skin, can also be shown as red, brown and other colors, usually painless and itchy. 3. Purpura: It may be thrombocytopenic purpura or allergic purpura, which can be induced after being subjected to external forces, and usually has no conscious symptoms. If the red spots on the arm are painless and itchy, you can observe them for a period of time. If they increase significantly or symptoms such as itching and pain appear, it is recommended to go to the hospital for examination in time.