Dry skin, acne, a flaky scalp and oily skin may all be related to your body's production of a substance called sebum. Scientists have studied sebum for years, and while they know what's in it and how it's formed, its exact function is still a mystery.
Sebum is a lipid, which is the scientific name for organic substances--such as oils and fats--that don't dissolve in water. Sebum's chemical makeup includes squalene, which is a building block for cholesterol; cholesterol and triglycerides; and an assortment of fatty acids and chemical salts. The exact chemical makeup of sebum varies little from person to person, according to "The Biology of the Skin," a book written for practicing dermatologists and residents in dermatology. However, the sebum in humans is quite different than the makeup of sebum in other species.
Your sebaceous glands, which are small glands attached to your hair follicles, manufacture sebum, though scientists aren't sure exactly how. The glands hold the sebum in fat droplets, and eventually push those droplets out into your hair follicle, where they coat the hair shaft and carry it up to the surface of your skin. Along the way, it picks up dead skin cells, dirt and bacteria.
Sebum may help your skin protect your body from bacterial infection by forming a barrier to keep microbes out, much like an ointment keeps dirt out of a cut or scrape. Sebum smooths the overlapping cells of hair strands, making your hair softer and more pliable. By extension, that helps your hair do its job of protecting your skin. Sebum also has antimicrobial, anti-inflammatory and pro-inflammatory properties, according to "Acne and Sebaceous Gland Functions," a 2004 review of studies that appeared in "Clinics in Dermatology." On the other hand, "the role of sebum remains unclear," with some scientists taking the stance that human sebum seems to be useless, according to "The Biology of the Skin" by R.K. Frienkel and D.T. Woodley.
Excess production of sebum appears to be a factor in acne, as does a difference in the chemical composition of sebum. Acne also appears to be related to hormone products, which also affect sebum production. Frienkel and Woodley note, too, that acne is an inflammatory disorder, and an imbalance in the inflammatory and anti-inflammatory actions of sebum may play a role.
Other skin eruptions also are related to sebum. When dirt and skin cells block hair follicles, sebum collects in the hair shaft and can't exit onto the surface of your skin. If the blockage is beneath the skin surface, the result is a whitish bump, called a whitehead. If the sebum reaches the surface, it oxidizes and turns dark, creating a blackhead.
Dandruff is made up of sebum and dead skin cells. Dry hair may result, in part, from sebaceous glands that don't produce enough sebum.
If your skin is oily, wash your face twice daily with a mild, anti-bacterial soap, advises University of California Student Health Service. Avoid heavy, oil-based makeup that can block your pores and trap sebum. Dermatologists treat acne with multiple approaches. For instance, peeling agents encourage the skin to shed cells; however, they don't reduce the production of sebum. Treatments also include antibacterials, such as benzoyl peroxide; antibiotic medications, which attack Propionibacterium acnes, the main bacteria present in acne inflammation; and an oral medication, 12-cis-retinoic acid, which must be prescribed by a doctor.