Red dots on the legs may be caused by papular urticaria, allergic purpura, periosteal keratosis and other causes. 1. Papular urticaria: common in hot summer, if the legs are bitten by mosquitoes, it is easy to induce papular urticaria, which may lead to red pimples on the legs, and may also be accompanied by pain, itching and other symptoms. 2. Anaphylactic purpura: It may be related to infection, food, drugs and other factors, which may cause red spots on the skin of the legs, which are slightly higher than the surface of the skin, and may be accompanied by symptoms such as swollen and painful joints, abdominal pain and bloating. 3. Perifollicular keratosis: related to autosomal dominant inheritance, vitamin A deficiency and metabolic disorders, it can make a lot of follicular red dots appear on the legs, and some of the hair follicles can be seen with curly hair and light brown keratin plugs. Red dots on the legs may also be caused by other reasons, you should seek medical attention as soon as possible, give targeted treatment after a clear diagnosis.