Ceramides

Ceramides are a class of lipid making up roughly half the lipid content of the stratum corneum, where they hold skin cells together and limit water loss.

How they work

The outer layer of skin is often described as bricks and mortar. Corneocytes are the bricks, and a lipid matrix of ceramides, cholesterol and free fatty acids is the mortar. That matrix is what stops water escaping and stops irritants entering.

Ceramide levels fall with age, with UV exposure, in cold dry conditions, and in barrier-impaired conditions such as eczema. Topical ceramides supplement that matrix directly rather than sitting on the surface as an occlusive film.

Reading the naming system

This is where ingredient lists become genuinely informative, once you know what the letters mean.

Ceramides are built from two parts: a fatty acid and a sphingoid base. The letters describe each. The first letter or letters denote the fatty acid, the last denotes the base.

Fatty acid: N for non-hydroxy, A for alpha-hydroxy, EO for esterified omega-hydroxy.

Base: S for sphingosine, P for phytosphingosine, DS for dihydrosphingosine, H for 6-hydroxysphingosine.

So the common ones read as:

Ceramide NP, also called ceramide 3, is a non-hydroxy fatty acid on a phytosphingosine base. One of the most abundant subtypes in human skin and the most common in formulation.

Ceramide NG, also called ceramide 2 or ceramide NS, is a non-hydroxy fatty acid on a sphingosine base. Also highly abundant in skin.

Ceramide AP, ceramide 6-II, has an alpha-hydroxy fatty acid on a phytosphingosine base.

Ceramide EOP, ceramide 1, is structurally distinctive, with an esterified omega-hydroxy fatty acid, and plays a particular role in holding the lipid layers together.

The older numbered system and the newer letter system are both in use, which is why the same molecule appears under two names.

Do the differences matter?

Modestly. All of these are genuine ceramides that integrate into the barrier. The subtypes have somewhat different roles in the lipid structure, and human skin contains a mixture rather than any single one.

Formulations combining several are closer to the natural composition than those using one. But a single ceramide is not a failure, and the position in the ingredient list tells you more about the amount present than the letters tell you about the quality.

The ratio matters more than the ceramide

Research on barrier repair generally finds ceramides work better alongside cholesterol and free fatty acids than alone, because it is the ratio between the three that determines how the lipid matrix organises itself. An imbalanced ratio can be less effective than a balanced one at lower total concentration.

This is why well-built barrier formulations include other lipids rather than ceramides in isolation.

Pseudoceramides

Some formulations use synthetic analogues rather than true ceramides, listed under names such as safflower oil/palm oil aminopropanediol esters or cetyl-PG hydroxyethyl palmitamide.

These are designed to mimic ceramide structure and function. They are generally cheaper and more stable, and there is reasonable evidence they contribute to barrier organisation. They are not the same molecules, and a product listing a pseudoceramide is not a ceramide product in the strict sense.

Source

Cosmetic ceramides are synthesised or produced by fermentation. They are not derived from animal tissue, despite occasional claims otherwise.