Sebum has many purposes. Once this oily substance makes its way to the surface of your skin, it keeps your skin waterproof. It's a barrier in two ways: It keeps too much water from getting into your body, and it prevents you from losing too much water through your skin. Sebum also protects skin from bacterial and fungal infections.
Sebum plays an important role in keeping your skin healthy, but too much sebum can also be bad for your skin. When hair follicles become clogged with sebum and dead skin cells, bacteria grow and cause acne [source: Mayo Clinic]. Clogged follicles below the surface cause whiteheads, and clogged follicles on the skin's surface cause blackheads. But sometimes the follicle wall can break down from the pressure of this buildup, and when this happens sebum leaks into tissue and forms pustules [source: WebMD].
You're born producing sebum, and you'll continue to produce it throughout your life, but certain factors can cause sebum production to increase and decrease. Sebum production is typically at its peak during puberty. In fact, the amount of sebum produced in males during puberty can more than double [source: New Zealand Dermatological Society]. Other hormonal changes can also trigger sebum production -- sebum often increases during a woman's menstrual cycle, during pregnancy and during menopause [source: American Academy of Dermatology]. As you age, your body typically produces less sebum, which is why older people are more likely to have dry skin [source: WebMD].
What exactly is in this oily secretion we call sebum? Keep reading to find out.