Sebum – Its Composition and Functions
Components of Sebum
Sebum is made up of lipids (fats) in different proportions that combine to protect the surface of the skin. The surface of the skin acts as a barrier that protects the internal structures of the body.
The fats in human sebum include triglycerides (57%), wax esters (26%), squalene (12%), and cholesterol (2%).1Human sebum is unique in this composition and differs from other mammals.2Furthermore, the exact composition of sebum differs from person to person based on the the micro-organisms present on the skin’s surface, the exact pH (acidity) of a particular person's skin, enzymes present in the skin, and the temperature of the environment at the time of measurement.1, 3, 4Researchers suggest that the individual differences in sebum composition may hold the key to a person’s chemical signature, potentially showing how dogs can recognize people after sniffing them.4
Functions of Sebum
Sebaceous glands are already formed and producing sebum while in the womb. In fact, sebum is a major component of the white substance called vernix caseosa that covers newborn babies.2It is theorized to help moisturize the fetus’s skin and make the passage through the birth canal easier, also while conserving heat, protecting the skin, and providing antibacterial effects for the newborn.
Throughout the lifespan of all mammals, sebum serves complex protective functions, including:
- Lubricating the surface of the skin and hair to prevent drying, thereby reducing damage from friction.
- Creating a barrier to make the skin waterproof and to prevent it from losing heat and water.2
- Possessing antimicrobial, pro-inflammatory, and anti-inflammatory properties.3
- Acting as a mechanism to transport and distribute antioxidants in the form of squalene, coenzyme Q10, and vitamin E, to the skin’s surface.
- Transporting pheromones, which are hormones that act on other mammals through smell, to the skin.1This might be nature’s purpose for the increased production of sebum during adolescence.
Only mammals have sebaceous glands, and thus, sebum. Sebaceous gland development and function are controlled throughout life by androgens, which are the male hormones present in both males and females.
In humans, sebaceous glands are found on all parts of the body, except on the palms of the hands and soles of the feet. They are most abundant on the face, particularly in the T-zone, followed by the neck and shoulders, and they are abundant also on the back and chest. The number and activity of sebaceous glands also varies with age and gender.4
Sebaceous glands are filled with specialized cells known as sebocytes. Sebum accumulates inside these cells, causing the cells to burst, releasing their contents into the hair follicle (pore). The sebum then slowly travels up the hair follicle until it reaches the surface of the skin.5
Sebocytes not only produce sebum, but together with skin cells they act as an immune organ to fight against invading microbes. On recognizing specific bacteria, such as P. acnes (acne bacteria), sebocytes and skin cells can react by altering the lipid composition of sebum and also by producing inflammatory and antimicrobial molecules to fight the "invaders."6
During embryonic development, maternal androgens regulate the development of sebaceous glands. The number of glands remains about the same throughout life, but they increase in size.2
During the lifespan, there is an increase in sebum production when the levels of androgens in the body are high. High levels of androgens are seen from birth to about one week of age, with a corresponding high level of sebum production, after which androgens and sebum production subside. Sebum production then increases again from about age nine, when the body starts producing androgens to prepare for puberty, until about 17 years of age, when androgen levels in adults are reached.
The pituitary gland, located in the brain, is a master gland that controls hormone production. However, interestingly, sebaceous glands themselves also produce androgens.2
The Role of Sebum in Acne
More sebum = more acne
Most teenagers who have acne will confirm the link between acne and oily skin, and acne researchers have established a clear link between increased sebum and more acne symptoms, but the exact process in which increased sebum leads to acne is not clear.
Imbalanced sebum = more acne?
Studies also have also shown that individuals who have acne display changes in the ratios of sebum lipids as well as in the composition of these lipids. For instance, people with acne tend to have fewer anti-inflammatory lipids in their sebum and more squalene, a pro-inflammatory (produces inflammation) lipid, in their sebum.7Since acne is primarily an inflammatory disease, this change in lipids may be part of the development or worsening of acne.
The changes in sebum lipids seen in people who develop acne also may also stimulate keratin production. Keratin is a sticky protein that makes up much of the skin. In other words, sebum with an imbalance of lipids may cause the skin to become thicker and stickier, thus leading to pore clogs.
Early studies found that people who had acne also had a decreased amount of a protective lipid called linoleic acid, in their sebum. The researchers postulated that low levels of linoleic acid were involved in increased skin cell formation in the pore, which contributed to the development of clogged pores. Low levels of linoleic acid also reduce the barrier function of the skin as well, which can make it is easier for inflammatory substances to penetrate the pore, perhaps leading to more acne.7
Most significantly, these changes in lipids, in combination with excess sebum, create an ideal environment for acne bacteria (P. acnes) to grow and multiply.3 Acne bacteria leads to more inflammation in the skin, and can make the redness and soreness of acne lesions worse.
Medications that reduce sebum also reduce acne
The fact that sebum contributes to the development of acne is supported by the fact that isotretinoin, an acne medication which destroys sebocytes, is effective in treating acne. Furthermore, hormonal therapy such as oral contraceptives and anti-androgens like spironolatone that reduce androgens in women, are known to reduce sebum levels and acne as well.2
Sebum is essential in maintaining healthy skin. However, too much sebum or an imbalance in the components of sebum may lead to acne. While treatment with isotretinoin and hormonal therapy both are effective in reducing the severity of acne, these treatments also come with side effects. Proper application of a topical skin care regimen can reduce sebum production and keep acne at bay until a person's hormone production calms down and acne naturally subsides.