Small rashes on the legs in hot weather may be caused by cholinergic urticaria, contact dermatitis, eczema, or other diseases such as insect bite reactions. 1. Cholinergic urticaria: Cholinergic urticaria is mainly caused by various factors such as exercise, stress, alcohol consumption, and eating hot food. The main symptoms of the patient are small and stinging bumps, itching without skin lesions, accompanied by tearing, headache, nausea, diarrhea and other symptoms. 2. Contact dermatitis: Contact dermatitis is usually an allergic reaction caused by contact with irritating, toxic or allergenic substances. The patient will have intensive papules, mild edema, erythema and other symptoms. In addition, contact dermatitis can also lead to erosion, oozing, crusting and other symptoms. 3. Eczema: the cause of eczema is not yet clear, and it is currently considered to be caused by the patient’s own disease or contact with other allergens. The main symptoms of patients are papules, blisters, edema, erythema, etc., and itching, vesicles, oozing, flaking and other symptoms. 4. Other: insect bite reaction, stasis dermatitis and other diseases can also lead to the phenomenon of small rashes on hot legs. Patients with symptoms of a small rash on the legs in the heat of the day should consult a doctor for timely examination and treatment as prescribed by the doctor.