Aesthetic nurse Lorna Bowes and consultant dermatologist Sandeep Cliff detail the importance of understanding the role and properties of moisturisers when recommending products to patients
As cosmeceutical companies continue to charge a premium for luxury brand moisturisers, how often do the public consider the scientific evidence supporting why moisturisers actually work and which type of moisturiser is most appropriate for them?
The UK female population is estimated to spend, on average, £131.95 on cosmetics annually.1 The reality being that many individuals will spend more than this amount on any one single ‘anti-ageing’ cream or serum. Moisturisers may be infused with gold, contain almond extracts or simply demonstrate luxurious packaging and design. Yet moisturiser is defined as ‘A cosmetic preparation to prevent dryness to the skin.’ In reality what patients are really seeking from moisturiser is, quite simply, water.
One 2010 study,2 funded by Olay, found that skin hydrated with daily moisturiser aged objectively less over the course of eight years than those who did not maintain adequate methods of skin hydration. The demand from consumers and the experience and results from dermatologists agree that the hydrating qualities of moisturisers make them a worthwhile and beneficial product to use on patients for anti-ageing.
Yet, despite the population’s readiness to part with significant sums of cash in exchange for this ever-popular, ever-used daily routine, many admit to knowing little about the mechanism of action of their favourite preparation. Do they appreciate the difference between why they are purchasing a daily serum as opposed to a thicker, more occlusive night cream? Do they understand what the term ‘occlusive’ means to their skin? Should they purchase the same moisturiser as their friend or should they consider their own skin type?
Moisturiser: According to the Oxford English Dictionary (OED) a moisturiser is a cosmetic preparation used to prevent dryness in the skin. In short, it is a substance that when applied to the skin adds water and/or existing levels of water in the stratum corneum (SC).
Humectant: Again, according to the OED, a humectant is a product retaining or preserving moisture. For example, natural humectants in the SC absorb moisture from the atmosphere, increasing the hydration levels in the outer SC.
Occlusive: The OED medical definition of occlusion is: The blockage or closing of a blood vessel or hollow organ. The word ‘occlusive’ is the adjective derivative and is described as ‘of or being a bandage or dressing that closes a wound and keeps it from the air’. In cosmetics, it is the covering and keeping from the air that is relevant.
Emollient: Defined as, “having the quality of softening or soothing the skin”, by the OED.
The outer layer of the skin is the stratum corneum; it comprises mature keratinocytes and on average is 15 cell layers thick.3
The structure of the stratum corneum has frequently been described as similar to ‘bricks and mortar’; the keratinocytes being the ‘bricks’ and lipids and amino acids making up the majority of the ‘mortar’.3 As well as amino acids, other osmolytes in the stratum corneum such as glycerol, lactic acid, taurine and urea act as humectants.4
The stratum corneum layer, sometimes known as the ‘horny layer’, contains natural moisturising factor (NMF). NMF is a combination of low molecular weight, water-soluble metabolites of laggrin, lactic acid and urea. NMF is osmotically active with strong humectant properties and its precise composition varies between individuals and different environments.5 The role of NMF is to prevent transepidermal water loss (TEWL). TEWL was described by Kligman as insensible water loss through the skin via diffusion and evaporation, making it therefore different to perspiration.6 Due to it’s considerable humectant properties (it is composed of the aforementioned water-soluble chemicals), NMF allows the SC to remain hydrated even in very dry environments.3 The lower layers of the skin, including the layers of the stratum compactum, are hydrated by body fluids rather than the humectant properties of the SC.4
NMF is water soluble; therefore, by it’s nature of being very superficial, is prone to being literally ‘washed away’.6 The ‘mortar’ layer of lipids, such as diglycerides, triglycerides, fatty acids, cholesterol and wax esters, is essential to seal the keratinocyte layer and in turn reduce TEWL.6 It has been clearly shown that inherited lipid metabolism deficiencies lead directly to dry skin conditions such as ichthyosis.7 The lipid ‘mortar’ serves a dual function, also preventing entry of bacteria and water-soluble agents. Sebum production is also important here, as sebum produces glycerol, which is vital for maintaining the skin barrier function.8 Excess sebum certainly leads to oily skin and contributes to acne, however we need to remember the vital function of sebum in treating patients with all skin types, and make skincare choices that work with the natural biology of the skin for best results.
Proper hydration of the stratum corneum as a key factor in the maintenance of soft, flexible, healthy skin was reported by Blank in the 1950’s.9 Continuous loss of water through evaporation on the surface of the stratum corneum – at a speed faster than it can be replaced – leads to xerosis (dry skin).10 Add to this the frequent use of hot showers and baths (worse with hard water) along with foaming cleansers, bath salts, gels and body and face scrubs, as well as soaps and detergents, it is easy to see how we frequently wash away the healthy barrier function. Xerosis is a symptom of many dermatological conditions, but is of particular cosmetic and functional importance in the treatment of photoageing and promotion of skin health. It is possible to reduce dehydration in the epidermis by creating an oil lm that reduces evaporation, as well as using ‘chemical sponges’ that absorb and hold water within the SC. Moisturisers are a key therapeutic component in topical treatment of various skin conditions such as eczema, lamellar ichthyosis, psoriasis etc.11 A very positive side effect
of increased hydration is the reduction in apparent fine wrinkles that a hydrated skin exhibits.10 It is not surprising that ‘moisturisers’ are extremely popular.
There are three main categories of moisturiser – occlusives, emollients and humectants. Although the aim of all moisturisers is to increase moisture in the skin by increasing water content in the SC, they achieve this in very different ways
A carrier or vehicle ingredient is the base in which the ‘active’ ingredients are delivered. In the case of moisturisers, the vehicle is often also an active moisturiser. The group of cosmetic topical preparations that are known as ‘cosmeceuticals’ tend to comprise active ingredients in a vehicle base. By selecting the appropriate base with the ideal active ingredients it is possible to tailor skincare to patients individual needs, for example providing a ‘moisturising base’ with active humectant ingredients to address both water dry and lipid dry skin.
There are three main categories of moisturiser – occlusives, emollients and humectants. Although the aim of all moisturisers is to increase moisture in the skin by increasing water content in the SC, they achieve this in very different ways. The key effects required to increase water content are to reduce evaporation, increase the integrity of the skin barrier, and increase levels of NMF and other humectants. Most moisturiser products are a combination of different moisturising agents, and are designed to be ‘cosmetically elegant’. This is not an easy task as many of the moisturising agents available are sticky and ‘heavy’ in consistency. A key to effective moisturisation is to produce a product that is both effective and tolerable and therefore encourages compliance i.e. regular topical application – a product that stains clothes, leaves skin sticky or prevents the patients applying make-up will not be used regularly.
Moisturisers therefore come in different vehicle formulations (the vehicle usually being one of the moisturising ingredients) known as:
For cosmetic preparations creams, lotions and gels are the most commonly used moisturisers; serums tend to be carriers for active ingredients such as antioxidants.12
The main function of an occlusive is to trap water on the surface of this skin, reducing TEWL. Occlusives also act as emollients, because they smooth the skin, filling in the gaps and cracks in the SC between the corneocytes.13 The occlusive effect of these ingredients ends as soon as the ingredients are removed from the skin, so any effect is temporary. Petrolatum has been in use as a skin care product since 1872, and is frequently cited as the gold standard against what other moisturisers are compared due to it being one of the most effective occlusives reported.14 The ‘grease’ effect of petrolatum may not be tolerable, petrolatum is a highly effective occlusive but its greasiness can prevent it being an acceptable ingredient in cosmetic products. It is important to note however that petrolatum is also known to be non-comedogenic.19 Other occlusives frequently listed are mineral oils (a liquid mixture of hydrocarbons obtained from petroleum), squalene, beeswax and cannuba wax, silicones such as dimethicone and cyclomethicone, lanolin and shea butter.15 Increasingly, natural oils such as grapeseed, olive and sun ower are being added to this list. Linoleic acid, found in these natural oils, is an omega-6 fatty acid, which is able to provide structural lipids to improve skin barrier integrity.16
Humectants are ingredients that are able to draw water into the upper layers of the epidermis either from the atmosphere or from the underlying dermal/ epidermal layers. As well as the direct effect of hydration, the increased water content of the SC leads to reduction in fines lines. This has led to many humectants being labeled as ‘antiageing’ or ‘anti-wrinkle’ – which is misleading, as the humectant effects are simply temporary.16 However, there are humectants that have other properties that are ‘antiageing’ or ‘anti-wrinkle’ in addition to the straight increase in local, temporary hydration. Commoly used humectants are glycerin (glycerol), urea, hyaluronic acid and sodium hylaronate, sorbitol, propylene glycol (also an occlusive), and hydroxyacids. The hydroxyacid group of humectants is particularly interesting, as they also have widely reported antiageing properties. Lactic acid is an AHA found in milk, and is a component of the skin’s natural moisturising factor.17 The polyhydroxy acid gluconolactone is made up of multiple hydroxyl groups, as opposed to a single hydroxyl group like earlier AHAs (e.g. glycolic acid), this attracts water, providing enhanced moisturisation.18 Lactobionic acid, a bionic polyhydroxy acid derived from milk sugar, is a potent antioxidant with humectant properties that strongly attracts and binds water. It is suitable for all skin types19,20 and its unique hydra-film delivers moisture, softness and smoothness to the skin.13
Emollients are used to smooth and soften the skin. Many emollients are oils that have an occlusive (air tight) action that provide a barrier against water loss from the skin. They also fill in the gaps and cracks in the SC between the corneocytes.13 Common emollients are cetyl stearate, glyceryl stearate, octyl octanoate, decyl oleate, isostearyl alcohol.22
Patients frequently describe their skin as both oily and dry (combination), and this is not illogical. Dry skin is a result of a lack of moisture in the SC, whereas oily skin is a result of excess sebum production, so it is logical and possible to have dry AND oily skin. Frequently patients will present with oily skin on the face but dehydrated dry skin on the body where there are less sebaceous glands. earlier described, above, the group of emollients, occlusive and humectants, collectively known as ‘moisturisers’, can be chosen specifically to address the different types of ‘dryness’ and to ameliorate dry skin for patients with complex issues such as dehydrated acne prone skin. With an increasing list of single ingredients with multiple clinical indications and skillful formulation of actives in carrier vehicles, our challenge is to find clinically effective moisturising skincare that is tolerable and delivers to our patients multiple skincare needs.