The rules we are working under
Before the vocabulary, the constraints, because they explain the shape of what follows.
We name no brand and no product. We describe classes by what they do. We do not tell you what to buy, because a publication that explains ingredient classes by function cannot also be selling a specific product without one of those two activities corrupting the other. And we do not repeat claims we cannot support, which removes a great deal of what circulates about ingredients.
What is left is smaller than you might expect and more useful than a list of names.
Lipid components of the kind found between the cells
Function. The mortar between corneocytes is built from three broad lipid classes: ceramides, cholesterol and free fatty acids, arranged into ordered sheets. Preparations containing lipids of these types are formulated on the rationale that supplying material similar to what has been depleted supports the layer.
What can be said. The rationale is coherent and the classes are the right ones. What is much harder to say is that a given product delivers them in the right proportions to the right place in a way that reconstitutes ordered structure, which is the part that matters. Ordered arrangement, not quantity, is what makes a barrier.
Our position. A preparation containing these lipid classes is a reasonable thing to use on a depleted layer, and it will also be acting as an occlusive and an emollient, which is where a good deal of the observed benefit comes from. Be sceptical of language implying that a cream rebuilds your barrier, because barrier construction happens inside the skin.
Small water attracting molecules of the kind the skin makes
Function. Inside corneocytes sits a mixture of small water attracting molecules produced during the cell's final maturation. Several ingredient classes are chemically similar to components of that mixture and are used as humectants on that basis.
What can be said. They are genuine humectants and the rationale is sound. They are subject to the humectant caveat in the article on the three jobs: in dry air, without an occlusive over them, they can move water in the wrong direction.
Specific note. One of these classes behaves differently at different concentrations, acting as a humectant at low concentrations and having an additional effect on the layer at higher ones. That distinction matters, it appears in clinical guidance on dry skin, and it is one reason that concentration is not a detail.
Simple protective materials that do nothing else
Function. Some materials are used precisely because they are inert: they form a film, they do not react, they do not sensitise readily, and they have no biological activity to speak of.
What can be said. For a barrier that is compromised, this is a feature. A compromised barrier lets more through, so the fewer optional ingredients present, the better. The plainest preparations are frequently the most appropriate ones for badly affected skin, which is inconvenient commercially and true anyway.
| Class | What it is for | The limit worth stating |
|---|---|---|
| Occlusive materials | Slowing evaporation from the surface | They do not enter or repair the structure |
| Lipid classes as found between the cells | Supplying material of the right type | Ordered arrangement is what matters and only skin makes it |
| Small water attracting molecules | Holding water in and near the layer | In dry air, without a film over them, they can move water outward |
| Inert protective materials | Being present and reacting with nothing | They do nothing else, which is the point |
| Emulsifiers, preservatives, thickeners | Making the product exist and stay safe | Not there for your skin, and not sinister |
| Fragrance and colour | Sensory appeal | A common cause of contact allergy and of no functional benefit |
Ordering framework written by this publication from general skin physiology. It is not a measurement, it is not taken from any study, and no number in it is a reading.
Everything else on the label
Most of an ingredient list is not there for your skin. It is there so that the product exists as a product.
Emulsifiers hold oil and water phases together. Thickeners give a texture people will use. Preservatives prevent microbial growth, which is a safety requirement in any water containing product and not an optional extra. pH adjusters set the formulation's acidity. Antioxidants stop oils going rancid. Fragrance and colour are sensory decisions and are covered in their own article.
None of that is sinister. It is worth knowing because it explains why an ingredient list is long and why length tells you nothing about quality.
Claims we will not repeat
A short list, stated plainly.
We will not tell you that any ingredient repairs, rebuilds or restores your barrier, because barrier construction happens in the living layers of the skin and nothing applied joins that production line.
We will not attribute percentages of improvement to any ingredient, because we would be inventing the number.
We will not tell you that any ingredient is toxic, hormone disrupting or accumulating on the basis of the claims that circulate online. Cosmetic products in Great Britain are regulated, there is an enforcement regime, and disputes about specific ingredients belong with regulators and with the published evidence rather than with a website.
We will not tell you that natural is safer. Contact allergy to plant derived ingredients is well recognised, and essential oils are among the more common causes of it.
How to use this vocabulary
The point of a functional vocabulary is that it lets you ask better questions of a label.
Is there a meaningful occlusive component, or does this disappear in seconds. Are the humectants paired with something to hold the water in. Is there a fragrance, and does this skin need one. Is the list short, which matters more the worse the skin is. And is the claim on the front a description of a mechanism or a piece of theatre.
That is as far as we go, and it is further than a ranking would take you, because a ranking would require us to have assessed products, and we have assessed nobody and nothing.