Sebum is a big part of your skin and your hair as well.
Sebum is the skin's natural oil. It is produced by the sebaceous glands situated below the surface of the skin. Ducts from these glands open into the hair follicles and sebum is thus secreted out on to the skin through the hair follicle opening. The glands only become fully active at puberty. Sebum playes an important role: emulsifies with sweat and becomes the body's moisturizer, a thin layer of fat on the surface of the skin which helps slow the evaporation of water to keep skin supple and healthy. It is slightly acidic and antibacterial, providing extra protection from substances which harm the skin.
Sebum moisturizes the hair shaft, too, smoothing down each hair's scaly suyrface to keep hair silky, healthy and lustruous. There are extra glands on the head for this purpose, and glands are more closely distributed down the centralo panel of the face from forehead to chin, which is why the area readily becomes oily. Sebum production varies from person to person, creating the difference between dry and oily skin and hair. It is affected by hormonal changes and excessive sebum that is involved in problems such acne and blackheads. (when there is blockage of sebaceous gland ducts) While cleaning is important, so is trhis protective acid mantle on the skin. Cleanse twice a day, no more and preferably use ph-balanced products. Remember that over-astringent and medicated products designed to reduce oilness can stimulatesebum production, with the skin suddenly dry, the sebaceous glands spring into action.