The appearance of many small red dots on the legs may be related to allergic purpura, insect bite dermatitis, periosteal keratosis and other causes. 1. Anaphylactic purpura: related to allergic reactions induced by bacteria, viruses, food, drugs, etc. The appearance is similar to a bleeding spot, slightly higher than the surface of the skin, which mainly occurs in the lower limbs, mainly on the extensor side of the calf. 2. Insect bite dermatitis: after the insect bites the skin of the leg, due to the acid in the saliva, it can cause abnormal immune response of the body, and a lot of small red dots appear. 3. Perifollicular keratosis: related to autosomal dominant inheritance, vitamin A deficiency, and metabolic disorders, the typical manifestations are keratin plugs at the mouth of hair follicles and keratinized papules consistent with the location of hair follicles. It is recommended that those who have a lot of small red dots on the legs go to the hospital in time to clarify the cause of the disease and standardize the treatment under the guidance of the doctor, so as not to delay the condition.