How does a moisturiser work on skin?

You apply it every day, probably without thinking much about it. But if you've ever wondered why one moisturiser leaves your skin feeling comfortable for hours while another seems to do nothing — or why your skin still feels dry even though you're using one — the answer is in how they actually work.

And once you understand that, the difference between them starts to make sense.

What a moisturiser is actually doing

Your skin loses water constantly. It evaporates from your skin’s surface into the air around you — a process called transepidermal water loss (TEWL).

This happens all the time, even when your skin feels fine.

Your skin has an outer layer — the skin barrier — whose job is to slow that water loss and keep your skin protected.

Think of it as a seal. When it’s working well, your skin holds onto moisture more effectively. When it’s not, water escapes faster than it should, and your skin starts to feel dry, tight, and look dull.

A moisturiser doesn’t replace your skin barrier. It supports it — helping that outer layer do its job more effectively so your skin can hold onto moisture better.

Three types of ingredients, three different jobs

Most moisturisers work through three types of ingredients, each doing something different.

Humectants draw water into the upper layers of your skin, giving it that immediate hydrated, slightly plumper feel. Common examples include glycerin, hyaluronic acid, and panthenol.

Emollients smooth and soften your skin by filling the small gaps between skin cells, helping your skin feel more comfortable and supporting the structure of the outer layer. Squalane, shea butter, and plant oils are typical examples.

Occlusives sit on top of your skin and form a layer that slows how quickly water is lost back into the air. Dimethicone, petrolatum, and beeswax are among the most common.

A well-formulated moisturiser contains a combination of all three.

The humectants bring water in. The emollients improve how your skin feels and behaves. The occlusives slow that water from leaving again.

Each type depends on the others. A humectant can draw water into your skin, but without something on top to slow evaporation, that water can be lost again just as quickly.

What this means

A moisturiser works by bringing water into your skin and slowing how quickly it escapes — using a combination of humectants, emollients, and occlusives.

Once you understand that process, it becomes much easier to see why some moisturisers work better than others — and why all three types of ingredients matter.