What is the science behind moisturisation?

The word “moisturisation” gets used constantly in skincare — on labels, in routines, in advice from every direction.

But what is actually happening when a moisturiser works?

A moisturiser works by helping your skin hold onto water more effectively.

In some cases, it can also help your skin become better at doing this over time.

The problem moisturisation is solving

Your skin loses water constantly. It evaporates from your skin’s surface into the air throughout the day — a process called transepidermal water loss (TEWL), which simply means water escaping from your skin into the air.

This happens all the time, even when your skin feels fine. The question isn’t whether water loss is happening — it’s how quickly.

Your skin barrier — the outer layer of your skin — controls that rate.

When it’s working well, your skin holds onto water more effectively.

When it isn’t, water escapes faster than it should, and your skin starts to feel tight, look rough, and appear less even.

Moisturisation works by supporting this layer — helping your skin slow that water loss.

How moisturisers work at an ingredient level

Moisturisers work through three types of ingredients, each doing a different job:

• Humectants — draw water into the upper layers of your skin. Common examples include glycerin and hyaluronic acid.
• Emollients — smooth and soften the surface by filling small gaps between skin cells. Squalane and shea butter are typical examples.
• Occlusives — form a light layer on the surface that slows how quickly water escapes. Dimethicone and petrolatum are among the most common.

Together, these ingredients bring water into your skin and help keep it there.

This is why your skin feels less tight, looks smoother, and appears more even.

A moisturiser that contains only one or two of these types is only doing part of the job.

When moisturisation goes deeper

Some moisturisers go a step further.

Ingredients like ceramides, niacinamide, fatty acids, and panthenol help support the structure of your skin barrier itself.

Over time, this can help your skin become better at holding onto water on its own.

This means the moisturiser is not just helping while it is on your skin — it is helping your skin function more effectively over time.

What this means when you're choosing a moisturiser

The science of moisturisation comes down to one thing: your skin loses water, and a moisturiser helps slow that loss.

Every claim on a label — “hydrating,” “nourishing,” “barrier-supporting” — should connect back to that.

A moisturiser with humectants, emollients, and occlusives covers the core job.

One that also includes ceramides or niacinamide goes a step further — helping your skin hold onto water more effectively over time.

Once you understand this, you can look at any moisturiser and know whether it is doing the full job — or only part of it.