You could say that your body has a love-hate relationship with sebum. When you have just the right amount of this oily substance, it helps protect your skin. But if your skin has too much sebum, you'll probably be battling acne, and if it has too little sebum, you could end up with dry, cracked skin.
Sebaceous glands, which produce your body's sebum, are found everywhere on your skin with the exception of the palms of your hands and soles of your feet. Different parts of the body have different numbers of sebaceous glands. Your hands and feet don't have many, but your back, forehead and chin have the most -- anywhere from about 2,600 to 5,800 sebaceous glands per square inch (400 to 900 per square centimeter). Even your ear canal has sebaceous glands [source: New Zealand Dermatological Society].
Sebaceous glands have a rounded appearance, and they lie just below the surface of the skin in the dermis layer. Sebum eventually makes its way from the dermis to the surface of the skin through pores, or hair follicles [source: KidsHealth]. Sebum and hair follicles have a close relationship. A follicle is a tubular home for hair -- each hair gets its own follicle. A hair follicle begins in the subcutaneous layer of the skin underneath the dermis. The sebaceous gland usually meets the follicle in the dermis layer -- sebum is secreted from the sebaceous gland through the follicle.
Now that you know the basics of sebum, read on to learn more about what it does.
Function of Sebum
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.
Sebum is composed of lipids, or fats. Lipids don't dissolve in water, which is how sebum is able to create a barrier that traps some water in the skin and keeps other water out. Carbon, hydrogen and oxygen are all elements in lipids, and lipids are found in both plant and animal cells [source: Medicine Net].
Sebum contains a variety of different lipids, including cholesterol, glycerides, fatty acids, squalene, and wax and cholesterol esters, but the exact composition of sebum varies with a person's age. For example, a newborn's sebum is very similar to an adult's sebum. However, after about six months, the composition changes. Sebum in a young child contains more cholesterol and less wax and squalene. The composition changes again around the age of eight and then again during puberty [source: New Zealand Dermatological Society].
For information on sebum, see the links on the following page.
Related HowStuffWorks Articles
- American Academy of Dermatology. "Glossary." 2008. (Accessed 9/20/09) http://www.skincarephysicians.com/acnenet/glossary.html
- Brown, Sonya K., M.D. and Alan R. Shalita, M.D. "Acne Vulgaris, Folliculitis, and Rosacea." American Academy of Dermatology, 2009. (Accessed 9/20/09) http://www.aad.org/education/students/acnevulgaris.htm
- KidsHealth. "Your Skin." 3/09. (Accessed 9/21/09) http://kidshealth.org/kid/htbw/skin.html
- Mayo Clinic. "Acne." 4/30/08. (Accessed 9/20/09) http://www.mayoclinic.com/health/acne/DS00169
- Mayo Clinic. "Acne Treatments: Emerging Therapies for Clearer Skin." Mayo Clinic, 4/19/08 (Accessed 9/20/09)http://www.mayoclinic.com/health/acne-treatments/SN00038
- Mayo Clinic. "Cradle Cap." 6/6/08. (Accessed 9/20/09) http://www.mayoclinic.com/health/cradle-cap/DS01074
- Medicine Net. "Definition of Lipid." (Accessed 9/21/09) http://www.medterms.com/script/main/art.asp?articlekey=4168
- Medline Plus. "Medical Encyclopedia: Hair Follicle Anatomy." 11/13/06. (Accessed 9/21/09) http://www.nlm.nih.gov/medlineplus/ency/imagepages/9703.htm
- New England Dermatological Society. "Seborrhea." 8/16/09. (Accessed 10/5/09) http://dermnetnz.org/acne/seborrhoea.html
- New Zealand Dermatological Society. "Sebum." 6/15/09. (Accessed 9/20/09) http://dermnetnz.org/acne/sebum.html
- WebMD. "How Skin Ages." (Accessed 10/22/09) http://www.webmd.com/skin-problems-and-treatments/effects-of-aging-on-skin
- WebMD. "Understanding Acne: The Basics." (Accessed 10/22/09) http://www.webmd.com/skin-problems-and-treatments/understanding-acne-basics