The appearance of many small red dots on the lower legs may be related to the causes of allergic purpura, idiopathic thrombocytopenic purpura, and stasis dermatitis. 1. Allergic purpura: It is caused by bacteria, viruses, drugs, food and other factors that cause the body to undergo an immune complex reaction, resulting in inflammation of the blood vessels as well as the perivascular area. This inflammation will increase the permeability of the blood vessel wall, capillary rupture and bleeding, which will lead to the appearance of bruises and petechiae on the skin, and the erythema has the characteristic of not fading when pressed. 2. Idiopathic thrombocytopenic purpura: when the number of platelets decreases sharply, it will affect the normal coagulation of blood, resulting in the appearance of bleeding spots under the skin. 3. Siltation dermatitis: for example, varicose veins of the lower limbs can lead to obstacles in blood circulation, making the veins appear stagnant, which increases capillary permeability, leading to the appearance of eczema-like symptoms in the calves, manifested as erythema, bruises and bruises. When a lot of small red spots appear on the calves, it is recommended to go to the hospital dermatology department in time to clarify the cause of the disease and carry out targeted treatment under the guidance of the doctor, so as not to delay the condition.