Sebum is our skin’s best care product, and the skin barrier function is closely related to its role. Therefore, excessive cleansing not only damages the skin barrier function, but also stimulates the sebaceous glands to secrete more sebum. How does oil come out of the skin? What we call “oil” actually refers to sebum, which is a lipid produced by the sebaceous glands in the skin that secrete sebum and the cells of the stratum corneum that disintegrate. The face, back, and chest of the human body have a high density of sebaceous glands, so these parts of the body like to produce oil. Especially during the green pounding period, under the stimulation of androgen, the sebaceous glands help our body to work overtime to “produce oil”. Why is the skin more oily in summer? In fact, the sebaceous glands do not change with the seasons, but the amount of sweat on the surface of the skin increases when the weather is hot, which changes its surface tension and makes it easier for sebum to be distributed on the face, thus making the skin appear greasier to the individual. How to make oily skin not oily? In this book, there are two kinds of methods, “treatment of the root” and “treatment of symptoms”, for you to choose. The “root” solution is mainly for the sebaceous glands, only to inhibit its secretion, in order to sustainably reduce the role of the oil, generally through the use of drugs such as retinoic acid to achieve the purpose. However, the use of these medications can have some adverse reactions. Therefore, it is only suitable for oiliness caused by increased sebum overflow and related skin diseases. The “symptomatic” approach is the most used, but it has a shorter duration of time. Products such as oil-control cleansers containing surface-active substances, shrinking lotions containing salicylic acid and resorcinol, and foundations containing kaolin and synthetic polymer particles all work by temporarily removing or adsorbing excess sebum. However, they can only temporarily eliminate the symptoms of “oily face”. However, if you are able to do so, you can undergo intense pulsed light (IPL) or laser treatment. After the laser or intense pulse light acts on the skin, due to the photothermal effect, the sebaceous glands are thermally damaged, resulting in a decrease in the sebaceous gland secretion function and a decrease in sebum discharge, thus temporarily inhibiting the sebum secretion effect. This kind of photoelectric treatment has less adverse effects than medication, and the effect and time are better than skin care products and cosmetics.