A moisturiser acts on the outermost layer of the skin, which holds water in and keeps irritants out. Products work in three broad ways: by drawing water in, by slowing its escape, and by supplying the lipid material the layer is built from. Most combine them.
What is the barrier that gets talked about?
The barrier is the outermost layer of the skin: a compacted sheet of dead, keratin-filled cells embedded in a mixture of lipids. Dermatologists call it the stratum corneum, and the usual description of the barrier is a brick wall, with the cells as bricks and the lipid mixture as mortar.
Its job runs in both directions. Water is kept inside the body, which matters more than it sounds given how much surface area skin represents, and most external substances are kept out. Two functions, one structure, viewed from either side.
When the barrier is impaired, water leaves faster and things get in more easily. Skin becomes dry, and it becomes more reactive to substances that would otherwise have stayed on the surface. Anyone who has noticed that dry skin stings at products it once tolerated has observed a barrier failing at the second half of its job.
How does a moisturiser act on the barrier?
Three mechanisms are usually distinguished, and most products employ more than one.
Humectants draw water into the outer layer, from deeper skin and to some extent from the air. Glycerol and urea are familiar examples. On their own they can be a mixed blessing in dry conditions, since water drawn upward can then evaporate if nothing holds it.
Occlusives form a layer over the surface that slows evaporation. Petrolatum is the classic instance, and the property responsible for its effectiveness is the same one responsible for how it feels, so the greasiness and the performance cannot be separated however much anyone would like them to be.
Emollients in the narrow sense fill between the surface cells, smoothing texture and improving how skin feels immediately. Some preparations go further and supply lipid components resembling the mortar of the barrier itself, on the reasoning that rebuilding the barrier is better than merely covering a gap in it.
Why does the base matter more than the marketing?
Because the base is most of the product, and it is doing most of the work.
Ointments contain little or no water and are strongly occlusive. Creams are emulsions of oil and water, less greasy and more pleasant, and generally require preservatives because water permits microbial growth. Lotions carry more water still, feel lightest, and are the least occlusive. Gels are lighter again and suit hairy areas.
That progression is a genuine trade-off rather than a hierarchy. Greasier preparations do more for water loss and are less agreeable to wear; lighter ones are used more consistently. Consistency is not a minor factor: a product applied regularly outperforms a theoretically superior one applied occasionally, which is why clinicians ask what you will actually tolerate.
Two ingredients deserve mention for reasons unrelated to performance. Fragrance and preservatives are recognised causes of skin reactions, and a compromised barrier admits more of both. This is why unfragranced preparations come up so often in dermatology, and why a product that stings is worth mentioning rather than persevering with.
What is worth asking?
Ask which base suits your situation, rather than which product. A clinician can answer the first usefully, and the second depends on what you will actually apply.
Ask how a moisturiser fits with anything else you have been prescribed. Ordering and timing between preparations is part of a plan, and getting it stated in the room is far better than working it out from packaging.
Enquire about fragrance and preservatives if you have reacted to products before. This is one of the few areas where the ingredient list on the back is more informative than everything on the front.
Where cost or quantity is a factor, say so. Preparations intended for generous use get used sparingly when a tube feels precious, and a clinician would generally rather know.
What this page does not do
It recommends no product, no brand and no ingredient, and it gives no quantities, frequencies or routines. What suits your skin depends on your skin, and this page cannot see it.
Common questions
What is the difference between a moisturiser and an emollient?
In everyday use they overlap heavily. Emollient is the term more often used clinically, particularly for preparations intended to be applied generously and regularly to skin that needs it. Moisturiser is the commercial term, and the two words describe products with much the same purpose.
Does a thicker product always work better?
Not necessarily better, but differently. Greasier preparations generally slow water loss more effectively, while lighter ones are more pleasant and therefore more likely to be applied consistently. A product used properly usually outperforms a theoretically superior one used rarely.
Do the active ingredients on the front of the pack matter?
Less than the base does, in most cases. The bulk of a moisturiser is the vehicle carrying everything else, and it is doing most of the work on the barrier. Ingredients highlighted on the front are frequently present in quantities the label does not disclose.
Can a moisturiser irritate skin?
Yes. Fragrance and preservatives are recognised causes of reactions in some people, and skin whose barrier is already impaired admits more of whatever is applied to it. A product that stings on application is telling you something worth mentioning at a consultation.
How does a moisturiser relate to a prescribed treatment?
They do different jobs, and how they fit together is part of a clinical plan rather than something to arrange yourself. Anything about ordering, timing or interaction between products is a question for the person who prescribed the treatment.
Sources
- Atopic eczema — conditions — NHS (United Kingdom) · accessed
- Information and support for people affected by eczema — Eczema UK (United Kingdom) · accessed
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