The causes of itchy body when hot include hives, sweat herpes, prickly heat, ringworm and so on. 1. Urticaria: In case of hives, the swelling of the skin is triggered by the stimulation of allergens, so it itches when it gets hot. 2. Sweat herpes: the stimulation of sweat triggers the redness and swelling of the skin, so the body will itch when it gets hot. 3. prickly heat: due to hot and humid lead to sweat pore blockage, the skin will quickly occur of small pimples and blisters, so the phenomenon of itching. 4. Ringworm: When the skin is infected by fungi, these fungi can damage the skin barrier, and the symptom of itching when it is hot will also appear. Finally, it is recommended to go to the hospital in time to do a systematic examination of the phenomenon of itching when the body is hot.