There can be several hundred sebaceous glands per square centimetre on the face, and none on the palms of the hands or soles of the feet. This single difference explains why the forehead becomes shiny by mid-morning while hands become chapped in winter. Sebum is not a defect to be eliminated: it is one of the skin's defences, and becomes a problem only when its quantity or quality changes.
In summary
- Sebum is a mixture of fats produced by the sebaceous glands, concentrated on the face, scalp, chest and back.
- It protects the skin, contributes to the hydrolipidic film and brings vitamin E to the surface.
- Production depends mainly on androgen hormones, age and temperature.
- Washing more often does not reduce sebum: harsh cleansing worsens the skin without shutting down the glands.
- A cosmetic product does not radically change how much sebum is produced: it can absorb it, remove it gently, and limit shine and blemishes.
Article written by Elisa Avalle, founder of LeLang Skin Care and a dermocosmetics specialist. Cover image generated with the support of artificial intelligence.
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What sebum is and where it is produced
Sebum is produced by the sebaceous glands, which in most cases open into the hair follicle. Their method of secretion is unusual: the gland cells fill with lipids and then break down, releasing all their contents. Sebum travels up the follicle and spreads across the surface.
The glands are most densely distributed on the face, scalp, chest and upper back, the so-called seborrheic area. They are completely absent from the palms and soles. The structure of the skin and its appendages is explained in how the skin is made.
A note about the name: skin sebum should not be confused with tallow, the animal fat I wrote about when discussing beef tallow on the face.
What it is made of
Human sebum has a composition found in no other body tissue. In approximate proportions, it contains:
- Triglycerides and free fatty acids, the most abundant component, accounting for more than half.
- Waxes, about one quarter.
- Squalene, around 12%: it is a lipid typical of human sebum.
- Cholesterol and its esters, in small amounts.
Squalene is valuable but delicate: when exposed to UV rays and pollution, it oxidizes, and oxidized squalene is one of the factors that makes sebum more irritating and more conducive to the formation of comedones.
What it does
Sebum mixes with sweat and the lipids in the stratum corneum to form the hydrolipidic film, which slows water loss and keeps the surface soft. Some fatty acids in sebum also act against various microorganisms and contribute to the balance of the skin's pH.
There is also a lesser-known function: sebum is one of the main ways vitamin E reaches the skin's surface, where it acts as an antioxidant. This is why areas rich in sebaceous glands contain more of it.
What determines the amount
Hormones
The main regulator is androgens. The glands are active at birth due to maternal hormones, then remain almost dormant during childhood and become active again with puberty. In men, production remains higher and declines slowly; in women, it decreases more sharply after menopause. The menstrual cycle can also affect facial shine throughout the month.
Temperature and season
In warm weather, sebum is more fluid and spreads more across the surface: in summer, skin appears oilier even when the glands have not changed their activity. The opposite happens in winter.
Age and skin type
Oily skin has larger and more active glands; combination skin has them concentrated in the central area of the face. The differences are explained in the articles on combination skin and men's oily skin.
When sebum becomes a problem
Three different situations need to be distinguished, as they are often confused.
- Shine. This is simply a matter of quantity: the skin reflects light, makeup lasts less well, but there is no inflammation.
- Clogged pores and blackheads. Here, the quality of the sebum and the turnover of cells in the follicle also matter. How comedones form is explained in blackheads, and the complete picture is covered in understanding acne.
- Oily flaking and redness in the folds of the face and along the sides of the nose. It may be seborrheic dermatitis, which should be assessed by a doctor.
And on the scalp
The scalp is one of the areas with the most sebaceous glands: each hair grows from a follicle connected to at least one of them. Here, sebum lubricates the hair and protects the skin, but when there is too much, it runs down the hair shaft and weighs the hair down within a few hours. It also nourishes Malassezia, the yeast that lives on everyone's scalp and is involved in dandruff: this is why oily dandruff appears where sebum is abundant.
The same rule applies to the face. Washing your hair frequently with a gentle shampoo does not make it produce more sebum; a harsh shampoo irritates the scalp without reducing it. And if the hair seems wet rather than greasy, it may be sweat rather than sebum.
A cosmetic product acts on the skin's surface layers and does not treat acne or other clinical conditions, in accordance with EC Regulation 1223/2009. If excess sebum is accompanied by inflamed spots, scarring, flaking, or sudden changes, the right course is to see a dermatologist.
The myth that washing makes the skin produce more sebum
Many people with oily skin wash their face three or four times a day with harsh cleansers. The result is not less sebum. The glands respond to hormones, not to how clean the surface is; what you get is an irritated barrier, skin that feels tight, and often more redness.
In reality, the sebum removed is redistributed across the surface within a few hours, and the feeling that the "skin becomes oily again immediately afterward" comes from this. The solution is gentle cleansing twice a day, no more frequently.
What a cosmetic product can do
- Cleansing without irritation, with gentle surfactants and a pH close to that of the skin.
- Absorbing excess oil: clays and powders reduce shine for a few hours.
- Improving the quality of the skin's surface with active ingredients such as zinc PCA or niacinamide, which some studies have shown can reduce facial shine.
- Choosing lightweight textures and formulas designed not to feel heavy, without giving up hydration: oily skin can also be dehydrated.
- Protecting it from the sun, which oxidizes sebum squalene.
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The next step
Determining whether skin is oily, combination, or simply shiny from the heat is not always straightforward. The pharmacist at LeLang partner pharmacies and para-pharmacies can examine it at the counter and recommend a suitable routine.
Do you want to understand where to start?
Book a free virtual consultation: we will assess your skin together and create a tailored regimen.
Sources for this article
- Thiboutot D. (2004). "Regulation of human sebaceous glands". Journal of Investigative Dermatology, vol. 123, no. 1, pp. 1-12.
- Picardo M. et al. (2009). "Sebaceous gland lipids". Dermato-Endocrinology, vol. 1, no. 2, pp. 68-71.
- Thiele J.J. et al. (1999). "Sebaceous gland secretion is a major physiologic route of vitamin E delivery to skin". Journal of Investigative Dermatology, vol. 113, no. 6, pp. 1006-1010.
- Draelos Z.D. et al. (2006). "The effect of 2% niacinamide on facial sebum production". Journal of Cosmetic and Laser Therapy, vol. 8, no. 2, pp. 96-101.
- Regulation (EC) No 1223/2009 of the European Parliament and of the Council on cosmetic products.
Where to go next: How skin is structured · Blackheads · Do pores open and close?
Discover the products: Oily skin · Facial cleansers
