Sebaceous glands are tiny oil-producing glands embedded in your skin. Their primary job is to make sebum, an oily substance that coats your skin and hair to lock in moisture, keep skin flexible, and act as a first line of defense against bacteria and environmental damage. Nearly every one of these glands is paired with a hair follicle, and together they form what’s called a pilosebaceous unit.
Where Sebaceous Glands Are Located
Sebaceous glands sit in the middle layer of the skin (the dermis) and are found almost everywhere on the body. They’re densest on the face, scalp, and upper chest, which is why those areas tend to feel oilier. The palms of your hands and soles of your feet are the only areas that have none at all.
Most sebaceous glands empty their oil into a hair follicle’s canal, where it travels up and spreads across the skin surface. But a handful of “free” sebaceous glands exist without any hair follicle attached. These show up in some specific places:
- Eyelids: Meibomian glands, which produce the oily layer that keeps your tears from evaporating too quickly.
- Lips and inner cheeks: Fordyce spots, the tiny pale dots many people notice on the inside of their lips or along the lip border.
- Nipple area: Montgomery tubercles on the areola.
- Genitals: Tyson glands on the penis and free glands on the labia minora.
What Sebum Is Made Of
Sebum is an oily-to-waxy mixture, not a single substance. By weight, it’s roughly 30 to 60% triglycerides (the same type of fat found in cooking oils), 20 to 30% wax esters, 10 to 30% free fatty acids, and 10 to 20% squalene, a moisture-locking compound. Cholesterol and related molecules make up only about 2 to 4% of the total.
This blend isn’t random. Squalene and wax esters are relatively unique to human sebum and play an outsized role in waterproofing the skin surface. When sebum reaches the skin, bacteria that naturally live there break down some of its triglycerides into free fatty acids. Those fatty acids lower the skin’s pH, creating a mildly acidic environment (often called the acid mantle) that discourages harmful bacteria like Staphylococcus aureus while supporting beneficial microbes.
How Sebaceous Glands Produce Oil
Sebaceous glands use a secretion method that’s unusual in the body. The cells inside the gland gradually fill up with lipid droplets over the course of their life cycle. Once they’re fully loaded with oil, the cells rupture and disintegrate entirely, releasing their contents into the hair follicle canal. In other words, the cells themselves become the product. New cells at the outer edge of the gland continuously divide to replace the ones that were destroyed, keeping the process going nonstop.
This whole-cell breakdown is the reason sebum is such a complex mixture. It contains not just the fats the cells accumulated, but also fragments of cellular material, which contribute to the gland’s protective and antimicrobial functions on the skin surface.
Hormones Control How Much Oil You Produce
Androgens (a group of hormones that includes testosterone) are the main driver of sebum production. Sebaceous glands have receptors that respond to these hormones, and when androgen levels rise, the glands enlarge and produce more oil. This is why sebum output is relatively low in children, then ramps up significantly during puberty as circulating androgen levels climb.
The timeline of peak oil production varies by sex. In a large cohort study, skin surface sebum peaked around age 40 in women and around age 50 in men. Specific components peak earlier: wax ester secretion is highest between ages 15 and 35, while squalene output in men peaks between 20 and 40 before declining. In older men, overall sebum production stays surprisingly stable even into the 80s. For women, production drops more noticeably with menopause as estrogen and androgen levels shift.
How Sebum Supports the Skin Barrier
Beyond simple lubrication, sebum plays an active role in skin defense. The bacterium Cutibacterium acnes (formerly called Propionibacterium acnes) is one of the most common residents of the skin, and it feeds on sebum. As it metabolizes the fats, it produces short-chain fatty acids like propionic acid that lower the skin’s surface pH. That acidic environment helps suppress harmful pathogens and supports the survival of other beneficial bacteria.
Research has shown that the metabolic byproducts of C. acnes also stimulate skin cells to produce more of their own lipids, particularly triglycerides. This boost in lipid production strengthens the skin’s physical barrier, reducing water loss through the skin and improving innate antimicrobial defenses. It’s a cooperative relationship: the glands feed the bacteria, and the bacteria’s activity strengthens the skin. Scientists consider this a sign that C. acnes co-evolved with humans as a mutualistic partner rather than simply a passive bystander.
What Happens When Sebaceous Glands Malfunction
Acne
Acne is the most common condition tied to sebaceous gland dysfunction. It develops through four overlapping factors: excess sebum production, abnormal buildup of dead skin cells inside the follicle, overgrowth of C. acnes bacteria, and inflammation. When androgen hormones (particularly testosterone and insulin-like growth factor) push the glands to overproduce sebum, the extra oil combines with dead skin cells that fail to shed normally. This plugs the follicle, creating a microcomedone, the precursor to whiteheads, blackheads, and inflamed pimples. There’s a direct correlation between the amount of sebum someone produces and the severity and frequency of their acne breakouts.
Sebaceous Hyperplasia
In middle-aged and older adults, sebaceous glands can become visibly enlarged, a condition called sebaceous hyperplasia. These show up as soft, yellowish or skin-colored bumps, typically 2 to 9 millimeters across, most often on the forehead, cheeks, and chin. A telltale sign is a small central dimple (umbilication) in each bump, sometimes with tiny branching blood vessels arranged in a “crown” pattern around it. The glands are enlarged but structurally normal, with four or more sebaceous lobules clustered around a single hair follicle. These bumps are benign but are sometimes mistaken for basal cell carcinoma because of their appearance, so a dermatologist may examine them with a magnifying instrument to confirm the diagnosis.
Age-Related Dryness
As sebum production declines with age, skin gradually becomes drier, rougher, and more prone to flaking and itching. The reduced output of sebaceous and epidermal lipids weakens the skin’s moisture barrier, which is why older skin often feels tight and looks less luminous. This isn’t just cosmetic. A weakened lipid barrier means the skin is less effective at blocking irritants and retaining water, making age-related dryness a functional concern as well as an aesthetic one.