The phenomenon of itchy bumps on the hands when they are hot is usually considered to be caused by herpes sweating, heat contact urticaria and other reasons. 1. sweating herpes: usually symmetrical, easy to recur, can be manifested as itchy hands when hot, and the appearance of small bumps, small bumps are usually small blisters, slightly above the surface of the skin, and varying degrees of burning sensation. 2. Thermal contact urticaria: can be divided into congenital and acquired, congenital patients can be manifested as contact with warm water 1 ~ 2 hours after the appearance of itchy hands, accompanied by small bumps of symptoms. Acquired patients, usually after a few minutes of contact with warmer objects, small bumps with itching appear, and usually subside on their own. To summarize, for the phenomenon that the hands get bumps and itchy when exposed to heat, it is recommended that the hands do not come into contact with too many things during the flare-up of the disease and actively treat it. If necessary, go to the hospital.