What Is Sebum?

Why It's Produced and How to Fix Dry or Oily Skin

A cross-section of human skin.
A cross-section of human skin. BSIP/UIG/Getty Images

Looking for a sebum definition? Sebum is a light yellow, oily substance that is secreted by the sebaceous glands that help keep the skin and hair moisturized. Sebum is made up of triglycerides, free fatty acids, wax esters, squalene, cholesterol esters, and cholesterol. The oil on the surface of the skin isn't just made up of sebum, however. It also includes lipids from skin cells, sweat, and environmental matter.

Where Sebaceous Glands Are Located

Sebaceous glands can be found almost everywhere on the body, except on the palms of the hands and the soles of the feet. There is a greater concentration of sebaceous glands on the middle of the back, the genital area, and the face—particularly the forehead and the chin. Most sebaceous glands are connected to a hair follicle, although some open up directly to the surface of the skin, like the glands on the eyelids and the preputial glands and Fordyce spots on the genitals and upper lip.

How Sebum Is Produced

Before sebum makes its way to the surface of the skin, it combines with cells that are in the process of being sloughed off inside the hair follicle. When the follicle fills up, sebum spreads over the surface of the skin, making it moisturized and healthy. When this process works too well, it results in oily skin and hair, a condition that is known medically as seborrhea.

An excess of sebum, dead skin cells, and dirt trapped inside pores can also lead to acne. Conversely, when not enough sebum is produced, the skin becomes dry.

Why Sebum Is Important

If you get a lot of pimples, you might feel frustrated by sebum and wonder why it's necessary for the body to produce it.

Keep in mind that, beyond keeping the hair and skin moisturized, sebum serves other important purposes, including maintaining the skin's flexibility and acting as a barrier to protect the skin from bacterial and fungal infections. 

Factors That Affect Sebum Production

Sebum production is controlled by hormones—specifically, androgens like testosterone. During puberty, the sebaceous glands enlarge and the hormones become more active and produce more sebum. This is why ​acne is such a hallmark of adolescence. During puberty, males produce up to five times more sebum than females. Sebum production starts to decrease by age 20 and continues to slow with age.

The amount of sebum that your body produces can also be affected by certain diseases. For example, disorders related to the pituitary and adrenal glands, the ovaries, and the testicles can either increase or decrease sebum production. Starvation reduces production, and Parkinson's disease increases it.

Certain medications like oral contraceptives, antiandrogens, and vitamin A derivatives like isotretinoin are all known to reduce sebum production. Others, like testosterone and progesterone, are known to increase sebum production.

How to Fix Dry Skin

If your body isn't producing enough sebum, your skin might be dry, red, flaky, or itchy.

Dry skin is exacerbated by using soaps that are too harsh for the skin and taking frequent, long, hot showers. Luckily, dry skin can be treated easily and cheaply. After showering, pat the skin dry and apply a quality moisturizer all over the body.

Look for a moisturizer that contains ceramides, emollients, sorbitol, glycerin, or humectants. Thicker, greasier moisturizers contain ingredients like petroleum jelly and mineral oil. They're more effective, but they take a while to sink into the skin and can clog pores.

How to Fix Oily Skin

If you have the opposite problem and your body is producing too much sebum, your hormones are probably to blame.

Wash your face twice daily and use a gentle, exfoliating scrub a few times a week. Look specifically for skin products (like makeup) that are labeled "oil-free."

Always wash your face and remove any makeup before going to bed. Allowing that dirt, oil, and makeup to stay on your skin is just asking for trouble. If you wear makeup, be sure to keep your makeup brushes clean, too.

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