As you can see from this picture, sebaceous glands are located in the hair follicles of our body. The sebum is secreted here, then attach to the hair and migrate to the surface of our skin. Sebum is composed of about 25% wax, 41% triglycerides, 16% free fatty acids, and 12% squalane. It is a good source of Vitamin E, which can help with retarding oxidation of those fatty acids and provide some subcutaneous skin protection (underneath our skin).
When these wonderful lipids reach the surface, they change. The triglycerides are hydrolyzed to produce glycerine and free fatty acids (you soap makers might recognize this as saponification!) and the cholesterol is esterified (which sometimes offers that recognizable smell of oily hair or skin). These free fatty acids contribute to the acidity or pH of our skin surface. At the surface, the sebum blends with the stratum corneum lipids to produce a lipidic film that covers our skin.
We have sebaceous glands all over our body - except the palms of our hands and the soles of our feet - and the most active are found on our head, face, neck, shoulders, and thorax (don't I know this!). Hyperseborrhea, meaning too much oil produced, can be a function of the number of glands and how much they produce. Our sebum production is dependent on our genetic make-up, endocrine system, and environmental factors. We rarely produce sebum before age 7. It increases through adolescence, then declines until about age 50.
As a note, if you're over 50 and find you have dry eyes, this is because the Meibomian glands (modified sebaceous glands in our eyes that act as tear evaporation preventers) have reduced their sebaceous output. Apparently glycerin works really really to re-hydrate your eyes. Obviously not a diagnosis or treatment plan, just something I read recently.
Sebum can be a royal pain in the bum for those of us who produce too much of it, but it does serve a great purpose! It can help protect our skin from environmental and chemical insult, help protect against bacteria and fungi, and keep us looking younger (the oilier the skin, the fewer wrinkles we tend to produce). It makes our skin wettable as it is a natural surfactant, allowing oils and water to mix so we can clean our skin and hair.
Interestingly enough, although it can help reduce trans-epidermal water loss, it doesn't actually have an effect on how hydrated our skin can be. We can have really oily skin, but still show signs of dryness (itching and flaking, for instance). If you find yourself in a position of having oily skin that is really dry, glycerine is the answer! Yep, a lotion or gel containing a lot of glycerine really helps increase skin hydration and plasticity.
But it's not all hearts and flowers with sebum. (Check out this post on comedogenicity and acnegenicity to see the mechanisms of acne! I'm sure you don't want me to copy the entire thing here!)
If you have too much oil, I'm sorry to say there are no creams or lotions you can create that will reduce the amount of sebum you are producing in your skin or hair. The studies to date on over-production of sebum are inconclusive when it comes to topical products, except for retinols. The best idea of those of us who are normally to hyper-oily is to cleanse our hair or skin with mild cleansers. If we use harsh detergents, we can strip too much oil away and it will only come back a little quicker. Mild cleansing, followed with something nice to soothe our skin (if necessary) like a toner or oil-free moisturizer, is the key. For oily hair, mild cleansing followed by a non-oil containing conditioner is the best idea. (I'll get more into the details of this in a few days when we look at the oily skin type!)
Join me tomorrow as we take a look at different skin types and how we can create awesome products that will work with each one!