The appearance of small red dots on the lower legs may be caused by mosquito bites, contact dermatitis, allergic purpura, pigmented purpura dermatosis and other conditions. 1. Mosquito bites: when bitten by mosquitoes, small red dots may appear on the calves and be accompanied by certain itching. 2. Contact dermatitis: when the calf comes into contact with allergens or irritants, it may also cause skin metamorphosis or irritation, resulting in the appearance of small red dots, accompanied by itching, stinging, burning sensation. 3. Anaphylactic purpura: this disease is mostly seen in children, caused by various allergens stimulation leads to capillary rupture bleeding, manifested in the appearance of small red dots on the skin, at this time it is recommended to immediately consult a doctor for related treatment. 4. Pigmented purpura dermatosis: the etiology is unknown, gravity and elevated venous pressure are important triggers, often manifested as clustered pinpoint-sized red petechiae on the lower extremities, usually without conscious symptoms. There may be other causes of small red dots on the lower legs, it is recommended to seek medical advice, consult a professional doctor and relevant treatment.