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What a moisturiser does – and what research is beginning to reveal
Of all the classic skincare products, I consider moisturiser the most important, especially for the face. If I had to keep just one step in my skincare routine, it would be this one.
The name says exactly what the product is meant to do: provide moisture. At its core, a moisturiser is an emulsion, a mixture of two substances that do not naturally mix: water and oil. Only an emulsifier brings them together. In an emulsion, one component is distributed through the other as fine droplets, and this is what determines which type it is. In an oil-in-water emulsion, oil droplets are dispersed in a continuous water phase. These creams usually feel lighter on the skin. Milk is an example. In a water-in-oil emulsion it is the other way round: water droplets are dispersed in a continuous oil phase, and the cream is as a rule considerably richer. A moisturiser has a simple but important job: to keep the skin supple, replace lost moisture and create a temporary protective layer that helps reduce further water loss. It should also preserve the integrity of the skin barrier at all five levels: the mechanical, the chemical, the biochemical, the immunological and the microbiological.
The question is a fair one, because the third of the five barrier levels, the biochemical, is exactly that: an emulsion of water and lipids produced by the skin itself. The skin makes its own cream, and it makes it well. But this natural system is not always enough to support the skin day after day. Frequent washing and cleansing put the barrier under strain, as does dry heated indoor air. The skin loses water continuously through transepidermal water loss, which can be neither seen nor felt. It sheds up to 50 million cells from its outermost layer every day, and with them lipids, proteins and amino acids. And as we grow older, its capacity to replace barrier lipids in sufficient quantity declines. There are exceptions. Children's skin needs very little care and often needs no additional moisturiser at all. In most people the need begins to increase only gradually, from around the age of twenty. And when the skin does begin to need additional support, it rarely requires an elaborate high-tech cream. A well-tolerated formulation that supplies water and lipids serves the purpose. That is usually enough to cover the essentials of daily skincare.
Children's skin needs very little care and often needs no additional moisturiser at all.
There is an endless variety of skin types. In my experience over four decades of practice, most people can nonetheless be assigned, roughly, to one of three groups when it comes to choosing a moisturiser. Around 10 to 15 per cent have good sebum production and skin that tends to be oily rather than dry. It produces plenty of lipids of its own, and hydration matters more to it than additional lipids. These are usually younger people, though some keep this skin type all their lives. A light texture suits them, an oil-in-water emulsion with a low lipid content.
Around 70 to 80 per cent, the great majority, have skin that is neither markedly oily nor markedly dry. Left to itself it copes well with everyday demands, but through cleansing, heated indoor air and the turn of the seasons it continually loses both water and lipids. Both need replacing in roughly equal measure. This skin type occurs at all ages. A medium texture suits them, again an oil-in-water emulsion, but with a balanced ratio of lipids and moisture. Around 10 to 15 per cent have dry skin that is low in lipids. What they lack above all is oil, and without it the stratum corneum also holds water less well. This affects people in the second half of life in particular, along with those prone to asteatotic eczema or atopic dermatitis, and occasionally younger people whose skin simply needs more support. They need a rich texture, a water-in-oil emulsion with a high lipid content. Anyone who is unsure should begin with the middle option. If the cream feels too rich, move down a step. If the skin still feels tight, move up. In my clinical experience, people almost always choose a moisturiser that is too rich. In winter the skin often needs more support, because cold outdoor air and dry indoor heating both put the barrier under strain and lipid production cannot keep pace. Skin lipids are essential for retaining water in the stratum corneum. When they are missing, moisture is lost more readily as well.
Everything so far is well established. The more interesting question is one dermatology has only begun to investigate in recent years: whether daily skincare can influence inflammatory processes elsewhere in the body. A group led by Peter Elias and Mao-Qiang Man at the University of California in San Francisco published a pilot study in 2019. For 30 days, 33 older adults received twice-daily whole-body applications of a specially developed formulation whose lipid blend was modelled on the composition of the stratum corneum. Untreated older participants and a group of young volunteers served as comparison groups. Barrier function improved measurably, as did hydration of the stratum corneum. And then came the part nobody had expected: in the blood, levels of two inflammatory cytokines, interleukin-1β and interleukin-6, fell to close to those of the young comparison group. A third marker, TNF-α, dropped by more than 40 per cent, although here the difference from the untreated group did not reach statistical significance. The effect in question, then, is an anti-inflammatory one. What is remarkable is where it showed itself. The cream was applied to the skin; the cytokines were measured in the blood. That is why this small pilot study attracted so much attention. This is a finding, not proof. The study included only 33 participants and lasted just 30 days, and the authors themselves call for a larger investigation at the end of their paper. The result does, however, fit what we already know about the barrier.
The question sounds far-fetched at first. A cream works at the surface, and inflammatory markers are measured in the blood. The link between the two lies in the skin barrier. Ageing skin loses lipids, above all ceramides, free fatty acids and cholesterol. The barrier becomes more permeable. A compromised barrier is dry and constantly in need of repair: it sends out a constant stream of inflammatory signals in the form of cytokines, which pass into the blood and remain measurably raised there. When the barrier is supported externally, however, the skin appears to release fewer of these inflammatory signals. The skin is our largest organ. Even low-grade inflammation that causes no visible clinical symptoms may matter when it affects an organ of this size. And that is precisely the reasoning behind these investigations: an organ this large can affect the whole body, even when it looks perfectly healthy everywhere. Chronic low-grade inflammation is now considered one of the major drivers of biological ageing. The term for it is inflammaging. Raised cytokine levels are associated with a range of age-related diseases. The causes are varied and lie in metabolism, in the microbiome and in cellular senescence. The skin barrier may therefore play a larger role in these inflammatory processes than previously thought. And if that is so, a moisturiser would be more than a care product: it might have effects that reach beyond the skin itself. These findings change little about the daily routine. But they do change how we understand it.
There is nothing spectacular about a moisturiser. But it helps keep the skin barrier intact. And an intact barrier is the foundation for every other step in skincare. It also appears to help dampen persistent, low-grade inflammatory processes in the body. And here it is worth remembering that the face makes up only a small part of the body's surface. Both studies treated the skin across a wide area. Good skincare therefore does not stop at the neckline. Based on what we know today, those extra two minutes spent applying moisturiser may do more than we once thought.
