Sebum

Sebum is the oil produced by glands in the skin. It is part of the barrier: it slows water loss and carries vitamin E to the surface. Skin with none of it is not healthy skin.

How much you make is mostly genetic and hormonal. Heat and humidity increase it, which is why almost everyone in Bangladesh is oilier between June and September than in January. Diet plays a smaller role than the internet suggests.

The practical point is that sebum production responds to how you treat your skin. Strip it with a harsh cleanser and the surface is dry for about an hour, after which skin often produces more — the rebound that makes people wash again. Twice-daily gentle cleansing and a light moisturiser break that cycle for most people.

Sebum is also not the same as the lipids that hold water in. Skin can be oily and barrier-damaged at the same time, which is why an oily face can still feel tight. If that describes you, the answer is water and ceramides, not more washing.

Niacinamide may help with how much oil sits on the surface. Nothing stops production entirely.