In this article, I will take a closer look at the benefits and limitations of moisturisers. I pick out this product group as representative of various “cosmeceuticals” that are applied to the skin as creams, lotions, masks or the like and are supposed to unfold their effect by penetrating the skin. All products claim that they are good for dry skin. And some claim much more. And rightly so?
In my opinion, skin creams should be used to keep the skin moisturised and to prevent dry skin. Skin creams that work very well against dry skin are already available for surprisingly little money. This requires neither a magic formula nor any “revolutionary” new active ingredients. A good moisturiser from the drug store or pharmacy is usually enough to maintain good skin hydration, even for dry skin.
Anything more than that, beautifully packaged in fancy glass and glossy cardboard, is usually too much of a good thing. Futuristic-sounding active ingredients, new and revolutionary, are supposed to give the impression that the “serum” for 70 euros and above can do more than the classic moisturizer. From improving the skin’s appearance to the formation of new collagen tissue and the elimination of wrinkles. “Anti-ageing” is a buzzword that almost no cream can do without these days.
But in most cases, these are empty promises. It is true that one or the other cream will certainly succeed in superficially concealing fine lines and visually improving a coarse skin texture due to its swelling effect. And there are certainly a number of soothing active ingredient complexes that promise relief from various skin irritations. But any claim of a “rejuvenating” effect I put a big question mark over. Even when active ingredients are used that are promising in themselves (such as hyaluronic acid). The superficial application sets narrow limits even for the best active ingredient. I will explain why in the following.
Little to be achieved at the surface
The main reason for my doubt is the superficial effect that creams, lotions and similar moisturizing products have in common. It only extends to the top layer of the skin, the so-called epidermis. And even there, the vast majority of creams only reach the uppermost cell rows of the so-called “stratum corneum”. The problem with this is that the cells in this layer can hardly be “rejuvenated” because most of them are dead. Even the most sophisticated active ingredient will only achieve marginal effects here. To be more effective, it must penetrate deeper skin layers. Into the deepest layers of the epidermis or, even better, into the dermis, where the blood vessels run and the metabolic processes central to ageing take place.
But this is not so easy for creams, lotions, serums, and the like. That’s why, in my practice in Munich, I rely on techniques such as microneedling, with which active ingredients can be introduced into the deep layers of the dermis through micro-channels pierced into the skin. Microneedling is an ideal procedure to stimulate collagen synthesis in the dermis and support it with specifically administered anti-ageing active ingredients. But as you can already see at this point, to be able to assess the effectiveness of moisturizer products, a certain knowledge of the structure of human skin is a prerequisite. Especially concerning the outermost layer, the epidermis.
Therefore, I will start my further considerations with a brief introduction to the “layer model” of human skin. In addition, I will go into some elementary dermal metabolic processes that are important for the constant regeneration of the skin and its adequate moisturisation. Why dry skin develops in the first place and what you can do about it will then become immediately clear.
Anatomy of Human skin
The human skin is basically made up of three layers (from the outside to the inside):
- the Epidermis
- the Dermis
- the Hypodermis
The epidermis and the dermis together are often also called “cutis”. The cutis has a thickness of 1.5 to 4 mm, depending on the region of the body. The epidermis is relatively thin and measures just 0.1 mm. The dermis measures between about 1.5 and 4 mm. The hypodermis can be a few millimetres to several centimetres thick, depending on the amount of subcutaneous fat stored. The thickness of the skin also varies depending on gender and age.
The top layer of skin is the epidermis. It consists of several layers of a specific type of skin cell, the so-called keratinocytes. The epidermis is constantly renewing itself: new keratinocytes are formed in the lowest layers of the epidermis (basal layer, stratum basale) and then migrate to the skin surface (stratum corneum). The individual layers of the epidermis are thus nothing more than different developmental states of one and the same cell type during its migration or maturation.
Once on the surface, the keratinocytes transform into corneocytes (horny cells). As such, they form the outermost boundary of the skin before finally being shed as dead tissue. The complete cycle takes 2–4 weeks, during which the keratinocytes migrate from the deep basal layer to the uppermost layers of the stratum corneum. The epidermis, as the top layer of the skin, is thus a constantly renewing protective wall whose building blocks are formed in the deepest layer, then undergo a process of differentiation and maturation on their way to the surface, to finally serve as part of the protective horny layer, to die off and be replaced by the next generation of cells. As I said, this constantly happens. Without interruption, each person loses about 40,000 dead horn cells – per minute!
Between the basal layer and the stratum corneum, the epidermis has two further cell layers:
- In the spiny layer (stratum spinosum), which adjoins the basal layer, various cellular building blocks are provided to make the horn cells mature and to bind the finished horn cells together through “lipid cement” to form a resistant barrier.
- In the subsequent granular layer (stratum granulosum), the conversion of the still living keratinocyte to a dead horny cell takes place. In the process, the cell walls are strengthened and stiffened, the cells are further “cemented” together, and the cells are finally induced to suicide by dissolution of the cell nucleus and cell organelles. As solid cell bodies, thickly bound together by lipids, the dead keratinocytes form the outermost protective layer of the skin until, as mentioned, they are rejected and replaced by subsequent generations of cells.
What does this mean for our moisturiser? Skin creams and all types of cosmetics that work through the skin must first pass through this outermost protective layer of the human skin, the stratum corneum. This is not particularly thick, only 5–10 micrometres only, and has only 10-20 individual cell layers. Nevertheless, this layer turns out to be quite an effective barrier. Whether active substances can successfully penetrate the skin therefore depends, among other things, on their molecular size, the so-called “molecular weight”. It is measured in “Dalton”. As a rule of thumb, active ingredient molecules may only be a maximum of 500 Dalton in size to penetrate deeper through the skin barrier into the epidermis. However, the molecules of the active ingredients that are important for skin hydration and anti-ageing are many times larger.
Hyaluronic acid, for example, occurs in different molecular weights from around 1 million Dalton, more complex variants go up to several million Dalton. When cosmetics manufacturers advertise with significantly lower molecular weights of 1000 Dalton and below, it is because they do not use hyaluronic acid itself, but a derivative. For comparison: BOTOX is around 900,000 Dalton. This is also far above any possibility of penetrating deeper into the skin. A “BOTOX cream”, that sometimes flashes through Social Media, will therefore remain wishful thinking for the foreseeable future.
Another example is nicotine: the plant alkaloid has a very low molecular weight of only 162 Dalton and can therefore penetrate the skin barrier quite well. This is exploited in the well-known nicotine patches. The same principle also works with testosterone patches, as testosterone has a molecular weight of only 288 Dalton.
But the functioning of the skin barrier is not only important from the outside to the inside. For the maintenance of skin hydration, the barrier from the inside to the outside is at least as important.
WHY IS “FROM THE INSIDE OUT” equally IMPORTANT?
The barrier function of the stratum corneum from the inside to the outside is particularly important for maintaining sufficient skin moisture. The regulation of the cutaneous water balance is a central task of the barrier. The stratum corneum forms a kind of natural “vapour barrier” that prevents the human body from evaporating water too quickly through the skin surface and drying out as a result. In principle, the stratum corneum can be thought of as a thin film that lies on the skin and is almost impermeable to water and water-soluble substances. Its inner structure resembles a brick wall, in which large and thick corneocytes (they are actually the thickest cells in the human body) are stacked in rows on top of each other and firmly bonded with a “mortar” of epidermal lipids.
Various metabolic processes take place in the stratum corneum, the end products of which take on different tasks in the “protective wall”, partly of a chemical nature and primarily directed against external influences (bacteria, fungi), partly of a hydrophilic nature to regulate the moisture balance.
Natural Moisturizing Factor and Lipid-Mortar
In the upper area of the stratum corneum, amino acids are formed that function as a natural moisturizing factor (NMF) and are essential for the water-binding capacity of the outer horny layer. Together with the “kit” of epidermal lipids that binds the horny cells, NMF is the most important factor in maintaining skin moisture. And with it the suppleness and flexibility of the skin, as well as a fine skin texture and a rosy complexion. Diseases can lead to NMF deficiencies (e.g. ichthyosis vulgaris), which causes the skin to dry out and flake. Frequent washing with soap can also lead to a reduction of NMF and thus to dryness symptoms of the skin. A whole range of dermal cosmetic therapies are available to counteract a damaged NMF and effectively increase skin hydration.
Furthermore, a loss of epidermal lipids leads to skin dryness. Certain cholesterol-lowering drugs, for example, are known to affect the lipid content of the epidermis as a side effect. In addition, frequent cleansing with soaps or the incorrect use of liquid oils (olive oil) in skin care also lead to washout of skin lipids and thus to a disruption of the barrier function of the stratum corneum. And thus to dry skin and all its consequences, dermatological as well as visual.
The healthy stratum corneum has a moisture content of about 10-20%. If the moisture content falls below this level, the skin appears dry and flaky. If, on the other hand, the water content is far above 20%, swelling occurs and the skin looks like it has been in the bathtub for too long. This swelling (“maceration”) reduces the barrier function of the horny layer. The gaps between the bricks in our brick-and-mortar model widen. This is an effect that many cosmetics make use of to be able to introduce active ingredients through the outer barrier into somewhat deeper skin layers. Cosmetically induced swelling is called “occlusion” and cream ingredients that can do this are called “occlusives”.
I will not dwell on the dermis for long in this text. This may come as a surprise, as the dermis contains the collagen and elastin fibres that are so important for a youthful appearance of the skin and whose slowed regeneration is decisive for skin ageing. This is one of the reasons why most of my other blog posts so far have revolved around processes in the dermis, such as microneedling or PRP. The dermis should also be the primary target of all the active ingredients touted by cosmetic companies as having rejuvenating effects. Collagen, elastin, various vitamin and amino acid complexes, hyaluronic acid, etc… all these substances act primarily in the dermis.
BUT: It is difficult for externally applied care products to penetrate the dermis. The epidermis turns out to be far too insurmountable for that. Most of the active ingredients that make it into the skin from creams or lotions get stuck in the upper rows of the “brick wall” of corneocytes and epidermal lipids. A standard phrase of mine, which you may have read on the blog or on Twitter, is: “Hyaluronic acid that is supposed to be beneficial has to come out of a syringe.” Because that’s the only way it gets into the dermis. Via minimally invasive techniques such as injections or microneedling.
So let’s be clear: “Anti-ageing” promises of commercially marketed creams, serums, lotions, etc. see their effectiveness limited by three limits:
- Whether the active ingredients contained can actually have the effect they promise is not always proven by clear scientific studies.
- Even if the effect of certain substances has been proven, this does not mean that they will reach the skin depths to which they must be able to unfold their effect.
- In the superficial skin layers, that all these products can reach, they will only be able to exert their effect to a very limited extent, as the cells there are predominantly dead or have only a very short life span before they are rejected by the body as skin flakes.
So why use moisturizers at all?
Mit allem bislang Gesagten könnte man jetzt gut und gerne die Meinung vertreten, dass die gesunde Haut Feuchtigkeitscremes, Moisturizer generell und allerlei Arten von sonstigen „Cosmeceuticals“ gar nicht nötig hat. Aber das stimmt so pauschal auch wieder nicht. Denn einerseits gibt es Hautpartien, die besonders anfällig sind für Trockenheit, speziell im reiferen Alter, wie zum Beispiel die Lippen oder die Ellbögen. Und andererseits ist es so, dass wir in unserer modernen Gesellschaft einen tatsächlichen Bedarf an Moisturizern selbst erzeugen. Durch unsere ebenso penibel wie gründlich durchgeführten Wasch- und Reinigungsroutinen nämlich, ergänzt um allerlei weitere Maßnahmen der täglichen Körperhygiene.
Diese „Kulturtechniken“ schädigen die Schutzbarriere des Stratum corneum und führen so zu einem erhöhten Feuchtigkeitsverlust der Haut und in weiterer Folge zu Hauttrockenheit. Verstärkt werden können Schäden an der Schutzbarriere noch durch andere Faktoren, wie schädliche Umwelteinflüsse, Nikotinkonsum, Hormonprobleme, Stress usw. Gute Feuchtigkeitscremes wirken solchen Barriereschäden sehr effektiv entgegen.
Woraus bestehen Moisturizer?
Feuchtigkeitscremes und andere Moisturizer bestehen zumeist aus den folgenden Bestandteilen:
- Occlusives: Occlusives are substances that coat the skin with a kind of “vapour barrier” and thus reduce transdermal water loss. Occlusives are hydrophobic and often extend into the uppermost layers of the stratum corneum, where they support the barrier function of the intercellular lipids. Vaseline is considered the most effective occlusive substance. Silicones and silicone elastomers are also widely used occlusives. Furthermore, fatty acids such as lanolic acid, fatty alcohols such as lanolin alcohol or acetyl alcohol, mineral oils such as paraffin or squalene, phospholipids such as lecithin or vegetable waxes such as carnauba. The difference in effectiveness between petroleum and other occlusives is enormous: while 5% petroleum reduces transdermal moisture loss by more than 98%, lanolin and mineral oil-based occlusives score only 20-30%. However, occlusives that are too effective can also be problematic. Especially in body folds or in zones with increased moisture (armpits, genital area), there is a risk that the skin moisture in the stratum corneum increases to more than 40%, leading to maceration, which increases the risk of bacterial infections and fungal diseases. To circumvent this problem, occlusives are mostly combined with moisturizers.
- Humectants: The role of humectants, as the name suggests, is to absorb and buffer environmental fluid. This can mean both the moisture on and at the surface of the skin, as well as the moisture IN the skin. Especially in areas with low humidity, this can mean that the use of an inappropriate skincare product actually INCREASES moisture loss from the skin. For this reason, moisturizers are preferably combined with occlusives to avoid such an effect. Common moisturizers are hyaluronic acid, glycerine, gelatine, honey, panthenol, urea, alpha-hydroxy acids (e.g. lactic acid, glycolic acid) or sodium and ammonium lactate.
- Emollients: Emollients have the task of making the skin smoother and more supple. They are, so to speak, the “replacement mortar” with which lost lipids between the corneocytes in the stratum corneum are replenished. Accordingly, they consist of fats or oils, and often enough they are the same substances listed under 2. as humectants. All moisturizing creams owe their “creaminess” to the emollients, even if they do not otherwise contain any fat components. Emollients can have an astringent effect, such as dimethicone or cyclomethicone. The cosmetic products then usually advertise with “reduced pores”, “against oily skin” and the like. Or they are explicitly “moisturizing”, such as isopropyl palmitate, decyl oleate, jojoba oil or castor oil. Emollients often also have an antipruritic effect, which is why they are regularly an important ingredient of ointments for the relief of certain skin diseases (e.g. neurodermatitis).
- Emulsifiers: Emulsifiers have the task of keeping the hydrophilic (water-soluble) and hydrophobic (water-insoluble) substances contained in numerous formulations in stable contact. A distinction is made between anionic, cationic, amphoteric and non-ionic emulsifiers, chemically mostly surfactants. Newer substances in this group are, for example, coconut monoglyceride sulphate synthesised from coconut oil and glycerine. The alkyl polyglycoside consisting of sugar and fatty alcohols is considered to be a particularly skin-compatible, non-ionic surfactant of the younger generation.
- Preservatives: Since many commercial moisturizer products contain a large amount of water, they are subject to an increased risk of bacterial contamination. Manufacturers counter this risk by adding appropriate preservatives.
- Scents and pigments: For better appeal to the consumer, cosmetic products should smell and look good. Otherwise, these product components have no function.
- UV-Protection: One of the few arguments that clearly speaks in favour of a skin cream is its added protection against UV radiation. A high sun protection factor actually makes your skin cream an “anti-wrinkle cream”, although differently than the advertising promises. Natural sunlight is a major contributor to skin ageing, and a high UV protection in your skin cream will shield you from this. Therefore, if you have to choose a moisturizer, and you don’t know which one, always go for the one with the higher SPF. It’s simple.
- Botanicals: Aloe vera is a well-known representative here. The southern plant is very popular as a moisturizer in creams and lotions, although the results of studies are inconclusive. The same applies to its skin-soothing effect as after sun balm.
- Anti-ageing protection: The list of popular “miracle cures” is long and getting longer. In fact, as was recently stated in a SPIEGEL cover story, one has the impression that the cosmetics industry is specifically researching biochemical complexes that look good on the packaging as the “latest philosopher’s stone”, with names that sound as complicated as possible. Many of these active ingredients may have a benefit, others may not. You will probably only find this out by trying them yourself. But as already mentioned above: Due to the peculiarities of the skin anatomy, long-term rejuvenation effects seem rather unlikely.
How do I choose the ideal moisturizer?
From what has been said so far, there are already numerous indications for the choice of the individually suitable skin cream. In addition, it should be said that products with a low water content should be given preference, especially in the cold season. Creams with a high water content can lead to unattractive frostbite of the skin. Ointments (water in oil emulsions) are therefore more suitable when it is cold outside and a longer stay outdoors is planned.
For the normal season, it is best to choose products that suit your skin type (dry/oily). If you have oily skin or acne, you need a non-comedogenic product. However, you should also avoid creams with a high water content in all body regions that are at risk of maceration (armpits, intimate area, body folds). Due to the large number of cosmetic ingredients, you should also keep an eye on the risk of allergic reactions. And as already mentioned: If you have to choose between several creams, choose the one with the highest sun protection factor. This will turn your moisturizer into a real “anti-ageing” product.