Sebum 101: What Skin Oil Is, Why It Varies, and What Controls It

Sebum is the oil your skin makes, and it gets blamed for shine, breakouts and a lot of product spending. It is also a normal part of healthy skin. Here is what it is made of, what controls how much you make, and why oily skin is not the same as hydrated skin.

What Sebum Is Made Of

Sebum is made by the oil glands attached to hair follicles and released onto the skin surface. It is mostly non-polar lipids: triglycerides, wax esters and squalene^[1]. Human sebum contains about 13% squalene^[2]. This is different from the lipids that make up the barrier between skin cells, which are ceramides, free fatty acids and cholesterol^[1]. In other words, the oil on your surface and the barrier inside your skin are two separate systems.

What Controls How Much You Make

Hormones are the main control. Androgen-stimulated sebum production plays an important role in acne, and sebum production is also regulated by estrogens, growth hormone, insulin, insulin-like growth factor 1, glucocorticoids and others^[3]. This is why hormonal changes can alter how much oil your skin makes. On average, sebum is also higher in men^[4].

Other things matter less than people think. In a study of 94 teenagers, stress correlated with acne severity, yet measured sebum did not differ between high- and low-stress periods^[5]. Season matters: in a year-long study of Czech women, sebum was low in winter^[6]. All the authors of that study work at a company (Contipro), and it covered Caucasian women only.

Oily Does Not Mean Hydrated

This is the most common misunderstanding. Sebum is oil, and hydration is water in the outer layer. In a study of male skin, excess sebum was associated with impaired barrier function, and men who did not follow a daily routine had significantly higher sebum and water loss than men who did^[7]. The study was run at a cosmetics company (POLA), and it shows association rather than cause. So skin can be shiny and still dehydrated. Skipping a moisturizer because you are oily does not fix that. Our post on dehydrated vs dry skin covers this in more detail.

Can Skincare Change Sebum?

A little, in some people. A trial authors' background point is that most oil-control products work by absorbing sebum rather than reducing its production. Their own study found that 2% niacinamide lowered the sebum excretion rate in 100 Japanese volunteers at 2 and 4 weeks compared with placebo. In a smaller study of 30 Caucasian volunteers over 6 weeks, casual sebum level fell but the sebum excretion rate did not significantly change^[8]. So the effect exists, it varies, and it is modest. For more, see Niacinamide 101.

Living With Your Sebum

• Do not over-strip it. Harsh cleansing irritates the barrier, which is the opposite of what oily skin needs.
• Keep hydrating: use a light serum or gel moisturizer, even if you are oily.
• Expect seasons: oil tends to be lower in winter, so a routine may need a richer step then, as covered in our squalane post.
• Treat breakouts separately. Excess sebum is one factor in acne, not the only one; see Acne 101.
• See a dermatologist for very oily skin with persistent acne, particularly if cycles or other hormonal symptoms are involved.