The product secreted and excreted by the sebaceous glands is called sebum. It is a mixture containing a variety of lipids, mainly saturated and unsaturated free fatty acids, glycerides waxes, steroids, squalene and liquid paraffin. Sebum excretion to the surface of the skin, part of the attachment in the hair, play the role of moisturizing hair; the other most of the sweat glands and the stratum corneum discharged water and a variety of substances together to form a kind of covering the surface of the pores of the lipid film, also known as the surface of the sebaceous membrane, the role of which is to lubricate the skin, to maintain moisture, to prevent the skin from drying, cracking. The secretion and excretion of sebum is generally considered to be subject to neuroendocrine control and is closely related to factors such as ethnicity, age, gender and temperature. The sebaceous glands are the target organs of testosterone. Androgens can induce hyperplasia and hypertrophy of sebaceous glands and increase secretory activity, while large amounts of estrogen can inhibit the secretory activity of sebaceous glands. Androgen levels are high during puberty, so the sebaceous glands are enlarged and leafy, and sebum secretion is the most vigorous, easy to form acne in the face, chest and back, and other seborrheic areas due to excessive sebum secretion and pore blockage. And older people as they age. Androgens, especially testosterone levels are declining, sebaceous glands gradually atrophy, sebum secretion gradually reduced, so the elderly will be more and more dry skin, especially after menopause women performance is more obvious. Men, on the other hand, will have drier skin after the age of 70. In addition, the secretion of sebaceous glands and the environmental temperature relationship is also very close, the epidermal temperature rises when the amount of sebum increases, the skin temperature rises 1 ℃, sebum secretion rises 10%. In the winter sebum secretion with the lower temperature and secretion is reduced, so the elderly winter skin dryness is more obvious.