Small red dots on the skin like blood spots are considered to be caused by allergic purpura, insect bite dermatitis, eczema and so on. 1. allergic purpura: a skin disease that occurs in the capillaries and small blood vessels, mainly due to contact with allergens caused by the lower extremities, especially in the lower legs, often manifested as a pinpoint of blood, but also may be manifested as a soybean-sized petechiae, and some of the patients with a more serious condition, may involve the upper extremities. 2. Insect bite dermatitis: due to the bites of mosquitoes with strong toxicity, the allergic reaction caused by injecting venom can be manifested as small red dots on the skin, accompanied by itching symptoms. 3. Eczema: generally manifested as a small area or large area of the skin with small red papules, the specific cause of the disease is not clear, may be related to skin allergic reaction, often accompanied by intense itching. Skin with small red dots like blood may also be caused by other reasons, it is recommended to promptly go to the hospital dermatology department to find out the reasons for targeted treatment.