Blisters are generally referred to as blisters, and small blisters on the arms in hot weather may be caused by contact dermatitis, eczema, prickly heat and so on. 1. Contact dermatitis: contact dermatitis is considered to be related to contact with exogenous substances, and patients will have skin erythema, blisters, papules and other manifestations. If the patient’s body sweats a lot when the weather is hot or contact with special substances, resulting in contact dermatitis triggered by arm skin irritation, there will be symptoms of small blisters on the arm. 2. Eczema: the cause of eczema is not clear, considering heredity, blood circulation disorders, mental factors, environmental heat and other causes. Patients will have symptoms such as pimples, papules, small blisters, etc. Therefore, patients with eczema on their arms in hot weather may have small blisters. 3. prickly heat: prickly heat is due to in the hot and stuffy environment, the body a lot of sweat is not easy to be evaporated, so that the stratum corneum impregnated with swelling said. If the patient arm prickly heat will appear pinpoint-sized blisters, blisters around the red halo and other manifestations. It is recommended that patients with small blisters on the arm in time to seek medical attention, the doctor will be clear after the cause of the selection of targeted measures to treat, do not self-medication.