The phenomenon of itching on the whole body when it is hot may be physiological reasons, there may also be pathological reasons, such as summer dermatitis, cholinergic urticaria and other diseases. 1. Physiological reasons: the external temperature is high, may cause excessive water loss of the skin, resulting in dry skin, skin barrier function is reduced, the outside world of the slightest stimulus can be caused by itching and other discomforts, so it can be manifested as a hot on the whole body itchy phenomenon, which belongs to the normal physiological phenomenon, it is recommended that the patient out of the hot environment, the availability of moisturizers to alleviate the symptoms of itching. 2. Pathologic causes: (1) summer dermatitis: due to the hot summer climate and caused by a class of seasonal inflammatory skin diseases, usually with the hot environment, excessive sweating, dust stimulation and other factors related to the limbs, trunk symmetrical erythema, papules or blisters and other clinical symptoms, and often accompanied by itching. (2) cholinergic urticaria: a type of urticaria, due to exercise or eating hot drinks and other reasons and make the skin local center body temperature, prompting the cholinergic nerve impulse and release of acetylcholine, the role of mast cells and the onset of the disease, can also be manifested as a hot on the whole body itching phenomenon. If the above symptoms and exclude physiological reasons, it is recommended to enter the hospital in time to identify the cause of the disease and actively cooperate with the doctor for treatment.