What is your moisturiser doing for your skin?
Skin moisturisers range in price from $200+ for a 20ml bottle, to the cheap and not-so-cheerful petroleum-based creams sold for as little as $5 per litre. To work out whether your moisturiser is really giving you value for money, it might be worth considering what a moisturiser can really do for your skin, and whether claims made in marketing campaigns can be believed.
How do moisturisers work?
The name ‘moisturiser’ conjures up the idea of adding water to the skin. However, most people are surprised when they realise that the water component of water-based moisturisers evaporates within around 15 minutes of application (1). Despite this, the aim of applying a moisturiser is to increase hydration and improve barrier function in the skin – specifically the outermost cell-free layer of the epidermis, the stratum corneum (see image below).
Microscopic cross section through skin. The dark dots are nuclei – note that in the stratum corneum cells are dead and no nuclei are visible.
What does a healthy stratum corneum do?
The role of the stratum corneum is to form a barrier against the environment. This barrier has two main functions – it slows down water loss through the skin and protects the body from contact with substances that could cause harm. The stratum corneum is formed as cells in the epidermis divide and move from the innermost layer of the epidermis outwards to the surface of the skin. As cells mature they produce lipids, keratin and a mixture of compounds collectively known as Natural Moisturising Factor, or NMF. At the level of the stratum corneum, the keratin and lipid components form a physical and water-repellent barrier, while NMF attracts water to itself, thereby locking water in the stratum corneum. Adequate hydration of the stratum corneum is essential for proper barrier function, and permits important metabolic reactions to take place, such as those which allow the normal shedding of the outer layer of the stratum corneum.
What happens when the stratum corneum is not formed properly?
Dry looking skin, characterised by flakes, scales, sometimes accompanied by redness and irritation, is a result of a poorly functioning barrier in the stratum corneum. This can happen when there is an abnormal maturation of cells in the epidermis resulting in an improper formation of the lipid, keratin or NMF components; or uneven or poor shedding of the superficial layers of the stratum corneum. It can be caused by internal or external factors, but irrespective of the cause, a breakdown in the skin barrier results in increased exposure to potential irritants, which may result in a progression to chronic skin conditions such as dermatitis and eczema.
How do moisturisers affect the skin barrier in stratum corneum?
There are 3 main ways that moisturisers help to maintain the skin barrier:
- Occlusive agents – these form a film on the surface of the skin, thereby reducing water loss and increasing the level of hydration in the stratum corneum. They include most of the petrolatum and mineral oil, methicones, waxes and the plant butters. The most efficient of these are the petroleum-based oils which form a plastic-like film on the skin. For some, the occlusive efficiency of petroleum based creams is problematic, as they may trap bacteria and dirt under the skin resulting in skin infections. In a study of premature infants, petroleum cream-treated babies had a higher incidence of systemic candidiasis, a life-threatening fungal infection , than those who did not receive any moisturiser. It was considered that the occlusive petroleum-based cream provided an environment that allowed proliferation of these organisms. In a separate study of premature infants, babies treated with sunflower seed oil were 41% less likely to develop infections than those treated with petroleum creams (2). Because the fatty acids of plant oils form a less complete barrier, allowing the sebaceous and sweat glands to secrete more freely, some consider that they permit more physiological functioning of the skin whilst slowing down water loss (3).
- Emollients – essentially this means creating a smooth appearance to the skin by filling in the spaces between the shedding stratum corneum, and improving the skin’s softness and pliability. In the medical literature, ‘emollient’ is interchangeable with the term ‘moisturiser’. A number of ingredients have both occlusive and emollient properties. Common emollients include plant and animal oils (triglycerides), as well as synthetic substances such as decyl oleate, isopropyl palmitate and cetyl alcohol. Note that plant-derived fatty acids have been shown to improve barrier function in the skin (4), probably because they penetrate through the stratum corneum and into the cellular layers of the epidermis, (5) helping to replenish lipids and contributing to the formation of a more effective lipid component of the barrier (4). In contrast, petroleum-based moisturisers remain on the skin surface (2). Interestingly, not all plant oils are beneficial – studies have shown that pure olive oil, soy bean oil and mustard oils damage the barrier, whilst sunflower oil may improve it. In olive oil, this effect was attributed to its high oleic acid content, whilst the beneficial effects of sunflower oil are considered to be due to its high linoleic acid content (6, 7).
- Humectants – these are molecules which attract water to themselves, acting as water binders. When included in a moisturiser, they theoretically help boost the level of NMF in the stratum corneum, helping to maintain hydration and therefore barrier function. Commonly used humectants are glycerin, urea and propylene glycol. Humectants are water-soluble and so may be included in a moisturiser that has a water phase, but not in pure oil moisturisers. Some humectants are considered to have a counter-productive effect, drawing water out of the stratum corneum and epidermis and thereby having the opposite effect to what is intended (8). Therefore, in practice, not all humectants improve hydration of the stratum corneum, and require careful formulation to ensure they are achieving the desired effect.
What else is included in moisturisers?
Emulsifiers are present in all water-containing creams, since they are needed to allow the oil and water phases of the moisturiser to combine. It has been shown that some surfactants may weaken the skin barrier, increasing trans-epidermal water loss. In one study, (9), 5 out of 9 emulsifiers tested damaged the barrier in this way. When one considers that emulsifier molecules contain a hydrophilic (water attracting) and lipophilic (lipid attracting) component, a similar structure to detergents, it is conceivable that some of them may interfere with the all-important lipid component of the skin barrier.
Preservatives are included in all water-based creams, since water-containing products would otherwise permit the growth of bacteria and fungi. For some, preservatives are a source of skin irritation, and may result in skin reactions. There are also concerns about hormonal disrupting effects of some commonly used preservatives (10) as well as their potential effects on the balance of the microbial population of the skin.
Bioactives are molecules added to moisturisers with supposed beneficial effects on cells in the skin, usually with the promise of preventing or reversing ageing. Despite common claims on some internet sites, healthy skin is not efficient at allowing molecules to pass through it, and will not ‘absorb 90% of what is put on it’, since a healthy stratum corneum forms an efficient barrier to most molecules. In order to have an effect on the living cells in the skin, a bioactive must pass through the stratum corneum into the cellular layer of the epidermis or, with greater difficulty, travel through the epidermis and into the dermis, where the common targets of bioactives, collagen and elastin, are located. Simply adding a vitamin, anti-oxidant or other growth enhancing molecule to a cream does not mean it will reach a destination where it can have a cellular effect.
The Mokosh approach to moisturisers
Our philosophy is to work with the body’s own healing and regenerative capacity. This means using no synthetic ingredients, drawing instead on a variety of biocompatible plant oils and butters for their occlusive and emollient effects, thereby delivering a rich and varied array of organic and unrefined plant triglycerides, fatty acids and other essential nutrients to the skin. Because our moisturisers contain biocompatible fatty acids, they are able to replenish the lipid component of the skin barrier, and simultaneously slow down water loss from the skin without occluding important glands, permitting them to function normally. This approach helps to fortify the skin, nurturing the processes that build a strong and fully functioning barrier.
Because our moisturisers contain no water, they contain neither emulsifiers, some of which are known to damage the skin barrier, nor preservatives, some of which may have adverse long term health effects, and may also alter the skin microbiome.
Finally, because our ingredients are grown and processed under certified organic conditions, they are not contaminated with potentially toxic solvents, and are naturally rich in a variety of anti-oxidants as well as vitamins A and E, some of which may penetrate into the cellular layer of the epidermis. These are the form of bioactives we prefer to use – those found naturally in plants grown and processed organically and with minimal refinement. In the same way that plants grown this way are more nutritious to eat and less damaging to the environment, so too they are the ideal food for our skin.
(1) Blichmann, CW, Serup, J and Winther, A. (1989) Effects of single application of a moisturiser: evaporation of emulsion water, skin surface temperature, electrical conductance, electrical apacitance, and skin surface (emulsion) lips. Acta Derm Venereol 69: 327-330 http://www.ncbi.nlm.nih.gov/pubmed/2568053
(2) Campbell, JR, Zaccaria, E, Baker, CJ (2000) Systemic candidiasis in extremely low birth weight infants receiving topical petrolatum ointment in skin care: a case-control study. Pediatrics 105: 1041-1045 http://pediatrics.aappublications.org/content/105/5/1041.short
(3) Darmstadt GL et al (2005) Effect of topical treatment with skin barrier-enhancing emollients on nosocomial infections in preterm infants in Bangladesh: a randomised controlled trial. Lancet 365:1039-45 http://www.ncbi.nlm.nih.gov/pubmed/15781099
(4) Mao-Qiang et al (1993) Fatty acids are required for epidermal permeability barrier function. J Clin Invest 92:791-8. http://www.ncbi.nlm.nih.gov/pubmed/8102380
(5) Mao-Qiang et al (1995) Exogenous nonphysiologic vs physiologic lipids. Divergent mechanisms for correction of permeability barrier dysfunction. Arch Dermatol 131:809-16http://www.ncbi.nlm.nih.gov/pubmed/7611797
(6) Boelsma et al (1996) Assessment of the potential irritancy of oleic acid on human skin: evaltuation in vitro and in vivo. Toxicol in Vitro 10: 729-42 http://www.ncbi.nlm.nih.gov/pubmed/20650257
(7) Darmstadt et al (2002) Impact of topical oils on the skin barrier: possible implications for neonatal health in developing countries. Acta Paediatr. 91: 546-54 http://www.ncbi.nlm.nih.gov/pubmed/12113324
(8) Kraft JN and Lynde CW (2005) Skin Therapy Letter Moisturisers: What they are and a practical approach to product selection. 10:1-8 http://www.medscape.com/viewarticle/505759_6
(9) Barany et al (2000) Unexpected skin barrier influence from nonionic emulsifiers Int J Pharm 195:189-95 http://www.ncbi.nlm.nih.gov/pubmed/10675696