The importance of the barrier function of the skin is clearly illustrated in patients with third-degree burns who are at risk of death through dehydration. The barrier prevents water loss through the skin as well as entry of allergens or irritants and resides in the uppermost layer of the epidermis, the stratum corneum (SC).

The SC consists of between 10 and 30 stacked sheets of cells termed corneocytes embedded in lipid-enriched lamellae or membrane. This structure is analogous to a brick wall, with the corneocyte “bricks” enclosed by a lipid lamellae “mortar”. These stacked sheets are connected via corneodesmosomes, which resemble the steel rods within reinforced concrete and provide tensile strength (i.e. resistance to shearing forces) to the skin. In normal skin, corneocytes are filled with water and swell, creating a smooth barrier without any cracks between them.

To remain soft and flexible, the skin requires a water content of between 10 and 15%. This is derived from the lower levels of the epidermis and maintained by the presence of humectants (water-binding molecules) such as lactic acid, urea, glycerol and hyaluronic acid within the corneocytes, collectively referred to as “natural moisturising factor” (NMF). The barrier is further enhanced by the presence of a hydrolipidic film on the surface of the skin, which consists of a mixture of sweat, sebum and water.

Dry skin occurs when the water content of the skin drops below 10% and occurs as a result of a breach in the stratum corneum barrier. It is characterised by lower levels of NMF and a defective lipid lamellae leading to loss of water from the corneocytes, which subsequently shrink, leading to the formation of cracks between them causing greater water loss through the skin and the creation of an entry portal for allergens and irritants.

There are a number of potential causes of barrier defects, including genetic (e.g. eczema, psoriasis and ichthyosis), medical (e.g. diabetes, thyroid disease), external (e.g. soaps and detergents), and environmental (e.g. cold weather). Studies have illustrated how, when the humidity of the environment drops (e.g. during colder weather), the activity of the enzymes responsible for skin shedding (which rely on water) is decreased and this leads to incomplete shedding of corneocytes which are visible as skin flakes. Nevertheless, irrespective of the cause, dry skin can be effectively managed through the use of emollients.

Emollients

An emollient forms an essential component of topical therapy for patients with dry skin conditions. While there is a wide range of available products, emollients only contain three different ingredients, which can all be broadly categorised as humectants, occlusives and emollients, as shown in Table 1.

With respect to terminology, the words “moisturiser” and “emollient” are often used interchangeably though strictly speaking, as described in Table 1, emollients are components of a moisturiser, which is itself defined as a compound that adds water to the skin. For consistency, the term emollient will be used throughout this article.

 

Additional components

Emollients can also contain components with specific actions, such as antipruritics (e.g. macrogols, colloidal oatmeal), antiseptics (benzalkonium chloride, chlorhexidine) and ceramides, which form part of the natural lipids in the skin.

Mode of action

Once applied to the skin, the occlusives present in an emollient form an oily layer over the surface, which effectively prevents water loss. Alternatively, an emollient that contains a humectant draws water into the epidermis from the dermis, causing swelling of the corneocytes. In practice, emollients often contain a mixture of occlusives and humectants, as this provides a complementary action to improve skin hydration and therefore reduce dryness. However, it is worth noting that some emollients contain only occlusives (e.g. emulsifying ointment). The physical barrier created by the occlusives also prevents the entry of allergens and irritants, which is especially important in conditions such as atopic eczema.

Emollient formulations

There are five different types of emollient formulation with each designed for use in slightly different circumstances.

Ointments

An ointment base is anhydrous (with up to 80% oil) and consists of a semi-solid mixture of hydrocarbons (e.g. white/yellow soft paraffin). Many ointments contain paraffin, and one recognised problem with products containing more than 50% paraffin (e.g. white soft paraffin, emulsifying ointment) is that they are a potential fire hazard, particularly if they are used over large areas of the body and the patient is in close proximity to or using naked flames or smokes.1 In fact, even dressings and clothing that have had contact with the flammable emollient can be easily ignited by a naked flame.

 

Dry skin occurs when the water content of the skin drops below 10% and occurs as a result of a breach in the stratum corneum barrier

Creams

A cream is a semi-solid formulation that contains the drug dissolved or dispersed within the base. Most creams are oil-in-water emulsions, in which a small amount of oil is dispersed in water. Oil-in-water creams are cosmetically acceptable formulations and less greasy than ointments.

Gels

A gel is composed of two interpenetrating systems. One of the molecules forms a three dimensional structure that traps the other molecule within.

Lotions

A lotion is an oil-in-water emulsion with a very high water content (between 70 and 80%) that spreads very easily on the skin and generates a cooling effect.

Sprays

These normally contain white soft paraffin and/or liquid paraffin in a solvent which evaporates when applied to the skin.

The indications for the different formulations and their benefits and potential drawbacks are described in Table 2.

Patients with dry skin are advised to practice “complete emollient therapy”, which involves the use of a leave-on emollient and products with which to wash and bathe or shower.

Emollient bath and shower products are available, but there is a lack of evidence for their effectiveness as highlighted in a recent study,2 and while frequently prescribed, they are generally not recommended, as most leave-on emollients are also suitable for washing and bathing.

Choosing an emollient

There are no specific rules on what is the best type of emollient and a recent Cochrane review concluded that, at least in the management of eczema, there was no evidence to demonstrate superiority for any particular emollient.3 Nevertheless, since patients effectively “wear” an emollient in much the same way as cosmetics, consideration should be given to their preferences, which will be influenced by the nature of their work and/or social activities. Another factor to consider is the severity of the skin dryness. In general terms, very dry skin will benefit from an ointment or cream containing a humectant, whereas mild dry skin can be managed with a lotion or cream.

In reality, patients often require more than one emollient product; a less greasy, cosmetically-acceptable product for use during the day, and a heavier (or greasier) product for nigh time use.

The cost of an emollient should also be considered, and most clinical commissioning groups (CCGs) have a local formulary with recommendations on which emollients to prescribe. Nevertheless, whether these formularies have an impact on prescribing decisions is debatable. A recent study4 that retrieved 102 formularies from CCGs in England and Wales, found 109 different emollients and 24 bath additives being recommended. The top five suggested emollients were white soft liquid paraffin, emulsifying ointment, Hydromol ointment, Dermol 500 lotion and Cetraben cream.

However, when compared with national community dispensing data, only two of these emollients (Cetraben and Dermol 500 lotion) were in the top five dispensed emollients. The reasons for this discrepancy were unclear, although it was speculated that possible explanations included lack of familiarity with the products and clinician/patient preferences. It was concluded that these differences would lead to an inequitable regional variation in care; in other words, a “postcode lottery” that was hard to justify. This variation has a potentially negative effect on patients who may no longer be able to obtain their preferred emollient, and this could be a problematic if they move to a different area.

A further problem for patients and prescribers is the recent NHS England guidance designed to restrict the prescribing of medicines that were available for purchase over-the-counter (OTC). The guidance suggests to CCGs that a prescription for dry skin (i.e. emollients) should not be routinely offered, as the condition can be self-managed with OTC products.5 However, the guidance does not apply to situations where the clinician considers that the presenting symptom is due to a condition that would not be considered minor, though this may be open to interpretation.

Emollients represent an active yet underused treatment in the management of dry skin conditions

Promoting patient adherence

In its guidance on the management of eczema, NICE recognised that emollients were under-prescribed.6 Furthermore, suboptimal use of emollients in patients with atopic eczema is associated with treatment failure.7 The provision of adequate advice and information on the correct use of emollients is therefore likely to result in better clinical outcomes as well as improving understanding and adherence.

In an effort to improve adherence, patients with a dry skin condition should be advised to:

  • Practice complete emollient therapy by avoiding the use of all soaps and detergents due to their drying effect on the skin
  • Use emollients liberally and frequently, even when the skin appears normal. For example, an adult with eczema requires up to 600g per week (2.4kg/month">2.4kg/month) and children 250g per week
  • After bathing/showering, pat the skin dry (rather than rubbing since this friction may cause irritation) and immediately apply their chosen emollients to increase skin hydration by trapping surface moisture
  • Simply dot an emollient onto the skin, spreading in a downward stroking motion (following the direction of hair growth) rather than rubbing in until it disappears
  • Use leave-on emollients as wash products. Unlike traditional soaps and cleansers, leave-on emollients do not create a lather or foam, but will still clean the skin and not lead to the skin dryness caused by soaps and detergents.

Using emollients with other topical therapies

It is currently unclear whether an emollient or topical steroid should be applied first to the skin. There are no specific rules, but the NHS suggests that if both an emollient and topical steroid are required, a 15-30 minute gap should be left between applications,8 with the emollient applied first, though there does not appear to be much of a rational to support this practice. In contrast, if both products are applied at the same time, there is a risk of diluting the topical steroid.

Case study

Emma is a 3 year old who has suffered with eczema from six months of age. She has a monthly repeat prescription for a 500g pump dispenser emollient and hydrocortisone cream 1%, which is reserved for eczema flares.

You have asked Emma’s mother, Carol, to bring her to see you because Carol appears to be over ordering hydrocortisone cream.

On examination you notice that Emma has dry and excoriated skin in the antecubital and popliteal fossae. Carol explains how Emma cries when applying the emollient and that it seems to make her skin worse. Carol therefore tends to use more of the hydrocortisone which quickly relieves the inflammation.

Potential solutions

Emma’s dry and excoriated skin is caused by insufficient use of her emollient, which appears to worsen her condition. You notice that the product contains cetyl alcohol, which is a known potential sensitiser. You therefore change to an alternative product.

You also note the 500g per month prescribed by your colleague is inadequate. According to NICE,6 children require up to 250g per week, and you prescribe 1kg of the new emollient and explain to Carol that it can also be used to wash Emma in the bath.

Two months later, at a routine appointment, Emma’s eczema seems to be under control and Carol has not ordered any more hydrocortisone cream.

Summary

Emollients represent an active yet underused treatment in the management of dry skin conditions. The challenge is to find a product that meets the needs of patients, and while this is dictated to some extent by the severity of the dryness, patient preference is an equally important consideration that requires a degree of trial.

Nonetheless, patients with cosmetically-acceptable products and an understanding of the need to use emollients regularly are likely to achieve satisfactory improvements in disease severity, regardless of the cause.

References

  1. MHRA. Paraffin-based skin emollients on dressing clothing: fire risk. Available at:
    https://www.gov.uk/drug-safety-update/paraffin-based-skin-emollients-on-dressings-or-clothing-fire-risk [Last accessed October 2018]
  2. Santer M, Ridd MJ, Francis NA et al. BMJ 2018;361:K1332
  3. Van Zuuren EJ, Fedorowicz Z, Christensen R et al. Cochrane Database of systematic reviews 2017, issue 2. No. CD12119
  4. Chan JP, Boyd G, Quinn PA et al. BMJ 2018; 8: E022009
  5. NHS England. Conditions for which over the counter item should not be routinely prescribed in primary care: guidance for CCGs. Available at:
    https://www.england.nhs.uk/publication/conditions-for-which-over-the-counter-items-should-not-routinely-be-prescribed-in-primary-care-guidance-for-ccgs/ [Last accessed October 2018]
  6. NICE. Atopic eczema in under 12s: diagnosis and management, 2007
  7. Cork MJ, Britton J, Butler L et al. Br J Dermatol 2003; 149: 582-89
  8. NICE Clinical Knowledge Summaries. Atopic eczema. Available at:
    https://cks.nice.org.uk/eczema-atopic#!prescribinginfosub:1 [Last accessed October 2018].

Rod Tucker

Pharmacist with a special interest in dermatology