Sweating in bed belongs to hyperhidrosis, and sweating in normal people after physical work and in hot environments on hot days is a normal physiological phenomenon and is not called hyperhidrosis. Hyperhidrosis is the phenomenon of abnormal excessive skin sweating. Hyperhidrosis can be confined to a certain area or generalized, that is, generalized hyperhidrosis and restricted hyperhidrosis. The sweat is secreted by sweat glands, which are divided into large sweat glands and small sweat glands. Large sweat glands are only found in a few areas, and small sweat glands can be found everywhere on the human skin, except for the red edge of the lips, nail bed, labia minora, glans and the inside of the foreskin. The small sweat glands open directly on the skin surface and are mainly innervated by cholinergic nerves. Patients who sweat a lot during sleep mainly in the occipital part of the head, and therefore have a wet pillow, belong to postural hyperhidrosis or pressure hyperhidrosis in restrictive hyperhidrosis. The mechanism may be related to the skin pressure receptors and the central cortical inhibition that controls sweating. Patients should first clarify whether sweating is related to mental changes, postural changes or too hot environment, and remove the cause of the disease.