What is “itch”? It is difficult for people to express clearly in words what kind of feeling “itch” is, which is completely reasonable, because itch itself is a complex sensation, with touch, pressure and pain, temperature, cold and other basic sensations are related. For example, gently stimulate the lips with cotton, can cause face and chin extensive itching; mosquito bites, the beginning of the stinging sensation, soon appeared local skin itching; mechanical stimulation of the armpits, can also cause extensive itching and euphoria in the trunk. So far, no special itch receptors have been found from histology, and it is generally believed that itch is closely related to nociception and may be conducted through free nerve endings or peripheral peripheral nerve network around hair follicles. Some scholars believe that itch is mainly transmitted by the epidermal dermal junction of the sensory organs and the superficial skin plexus. The mechanism by which itch occurs is complex, and most of the skin is accompanied by varying degrees of itchiness. Many internal and external factors, such as mechanical scratching, temperature changes, strong acid, acetic acid, formic acid, weak base, methyl bromide, mustard gas, insect venom, some plants (such as lacquer, cat’s-eye grass, nettle) and some of the body’s cellular damage to some of the substances produced (such as histamine, active proteases and peptides), etc., can be induced by itching. Some scholars have done experiments to prove that, after the injection of histamine into the skin, 20 ~ 30 within the injection of local skin itch, a few minutes after the appearance of “itchy skin” around the state, itching intensified, and lasted a long time. It is different from the normal itch, the former hard scratching does not solve the itch, the latter gently rubbing or scratching can stop itching. In addition, the organism internal organ lesions can also cause skin itching, such as chronic infection, diabetes, hyperthyroidism, liver disease, kidney disease, pregnancy, tumors, etc., and mental emotional factors, such as mental tension, emotional excitement, depression, anxiety, etc. can also be different degrees of itching caused or aggravated. In short, the mechanism of itching is more complex, to be further studied.