Emollients and moisturisers
What are emollients and moisturisers?
What are the causes of dry, scaly skin?
Dry, scaly skin may be due to:
- Dry air e.g. low winter humidity
- Exposure to the wind
- Reduction in production of natural moisturisers (sebum) in old age
- Diuretic medications
- Underactive thyroid gland
- Inherited factors
- A skin condition such as atopic dermatitis (eczema), psoriasis or ichthyosis
- Any combination of these
How does dry skin arise?
Dry skin results from lack of water in the stratum corneum, the outer, compacted layer of non-living cells that covers the entire body like a layer of cling film. When it becomes dehydrated this layer loses its flexibility and becomes cracked and scaly. The stratum corneum contains natural water-holding substances that retain water seeping up from the deeper layers of the skin. Water is also retained in the stratum corneum by a surface film of natural oil (sebum) and broken-down skin cells, which slows down evaporation (trans-epidermal water loss or TEWL.)
Causes of dehydration of the skin
Water loss from the skin is increased by dry winter air, either outside on cold, frosty mornings, or inside in centrally-heated homes or offices. Wind also increases evaporation from the skin. Increasing age means the skin holds less water, particularly over the age of 50. People on diuretics for hypertension (high blood pressure) or heart failure, and those with underactive thyroid glands also have drier skins.
Another important factor in encouraging water loss from the skin is over bathing. Washing with hot water and soap washes off the surface layer of natural oil, which goes down the plug hole. Unless the oil is replaced with either an oil or an emollient applied to the skin after washing, water loss from the skin increases and an hour or so after bathing the skin is drier than it otherwise would have been. Detergents and solvents similarly encourage dehydration of the skin by removing the surface oil film.
How does scaly skin arise?
Scaly skin arises from visible detachment of cells from the surface of the stratum corneum. In normal skin this process is invisible because the scale consists of individual cells. In scaly skin the cells have difficulty in detaching from each other and come off in little ‘rafts’ which are easily visible. This occurs in dry skin from any cause but also in eczema, psoriasis and ichthyosis where the skin cells are imperfectly formed and don't detach properly.
Treatment of dry skin
To correct a dry skin tendency from any cause reduce contact with soap and water and apply a moisturiser or emollient.
- Reduce washing to every second day, or less often, although the body folds may be sponged daily if desired.
- Baths or showers should be kept as brief as possible.
- Water should be lukewarm.
- Minimise the use of soap. Use a mild soap or better still, a detergent-based cleanser. Cleansers that have the same pH as the skin (5.5) may be advantageous.
- Reduce the need for bathing by keeping as clean as possible both at home and at work.
Moisturisers and emollients
The terms ‘moisturiser’ (to add moisture) and ‘emollient‘ (to soften) are interchangeable as they describe different effects of these agents on the skin. Basically they have two actions:
- Occlusives, which provide a layer of oil on the surface of the skin to slow water loss and thus increase the moisture content of the stratum corneum.
- Humectants, which are substances introduced into the stratum corneum to increase its water holding capacity.
Some moisturisers contain both occlusives and humectants.
Occlusive emollients consist of oils of non-human origin, either in pure form or mixed with varying amounts of water through the action of an emulsifier to form a lotion or cream. A large variety are available, reflecting that there is no '‘right’ moisturiser for all patients: the most suitable one often having to be found by trial and error.
- Bath oil deposits a thin layer of oil on the skin upon rising from the water.
- Lotions are more occlusive than oils. These are best applied immediately after bathing, to retain the water in the skin, and at other times as necessary.
- Creams are more occlusive again. Thicker barrier creams containing dimeticone are particularly useful for those with hand dermatitis.
- Ointments are the most occlusive, and include pure oil preparations such as equal parts of white soft and liquid paraffin or petroleum jelly.
The choice of occlusive emollient depends upon the area of the body and the degree of dryness and scaling of the skin.
- Lotions are used for the scalp and other hairy areas and for mild dryness on the face, trunk and limbs.
- Creams are used when more emollience is required on these latter areas.
- Ointments are prescribed for drier, thicker, more scaly areas, but many patients find them too greasy.
Sorbolene cream is a good all-round moderate-strength moisturiser that suits many patients because it is non-greasy, cheap and available in bulk without prescription.
250g (or ml) is a minimum quantity for an occlusive emollient and often 500g or 1Kg is needed: liberal and regular usage is to be encouraged. How frequently it is applied depends on how dry the skin is: very dry skin may benefit from a greasy emollient every couple of hours, but a light moisturiser may only be needed on slightly dry skin at night.
Humectants, agents adding water to the stratum corneum, include:
- Alpha hydroxy acids such as lactic acid or glycolic acid. At higher concentrations these also have a descaling or keratolytic action by thinning the stratum corneum: they are often known as peeling agents.
Urea and lactic acid preparations often sting if applied to broken (scratched or cracked) skin. Humectant / keratolytics are particularly important in management of the ichthyoses (inherited or acquired scaly disorders of the skin).
Adverse Reactions to emollients
- Irritant reactions - A common irritant reaction to occlusive emollients is ‘overheating’, resulting in a burning sensation. Some people experience stinging reactions from certain moisturisers, sometimes from most. This is particularly common in those with a tendency to atopic dermatitis or with rosacea. Stinging is often an irritant reaction to some component of the cream or lotion base rather than a true allergy. If irritation is only transient it may be decided to continue the preparation. However if the stinging is more troublesome, trial and error will generally find an alternative preparation which can be tolerated.
- Allergy - True allergy to moisturisers and emollients is rare. Suspected contact allergy can be investigated by patch testing. But even if a patient's allergens are identified, their presence in commercial preparations can be difficult to ascertain and it often comes back to trial and error.
- Folliculitis - Over-occlusive emollients can result in blocked hair follicles and painful pustules (folliculitis) or boils.
- Facial rashes - Over use of facial moisturisers, especially if they are occlusive, can aggravate acne or cause an unsightly rash, perioral dermatitis.
Other treatments for scaly skin
Emollients are always an important part of treatment for scaly disorders such as eczema, psoriasis and the ichthyoses. However, other agents are often needed to normalise skin cell formation and correct the scaling. These include: