Constituents of emollients

Emollient products are composed of a variety of constituent substances. Broadly speaking these can be divided into active ingredients and excipients. Active ingredients are those ingredients that exert a therapeutic benefit. Excipients can be described as the ingredients that allow the product to be effective but have no direct therapeutic benefit themselves. They will include preservatives and emulsifiers. Manufacturers are obliged to list the active ingredients and excipients of their products. It is worth noting that this listing does not always highlight the potential sensitisers within a product. For example, emulsifying wax contains cetostearyl alcohol which is a potential sensitiser. On products, only emulsifying wax will be listed. In general the British National Formulary will highlight when a product has a potential sensitiser in it. Other common constituents and their purpose are listed in Table 5.1.

Table 5.1 Potential sensitisers as listed in BNF and found as excipients in emollients.   Excipient Property   Benzyl alcohol Preservative   Butylated hydroxyanisole Preservative   Butylated hydroxytoluene     Cetostearyl alcohol (including cetyl and stearyl alcohol) Has moisturising properties (and emulsifying properties)   Chlorocresol Preservative   Edetic acid (EDTA) Improves product stability towards the air   Fragrances To make a product smell pleasant or to mask unpleasant odours   Hydroxybenzoates (parabens) Preservative   Imidurea Preservative   Isopropyl palmitate Thickening agent   N-(3-Chloroallyl)hexaminium chloride (quaternium 15) Preservative   Polysorbates Emulsifier   Sodium metabisulphite Preservative   Propylene glycol Humectant, preservative and stabiliser   Wool fat and related substances including lanolin (not generally thought of as excipient, but rather an active ingredient) Emollient   Sorbic acid Preservative

Emollients will always have some level of lipid in them. Lipid is a broad term used to describe different types of waxes, oils and fats (Marks, 2001). Oils are the most common lipids found in emollient products; these include vegetable oils such as sunflower oil, mineral oils such as petrolatum or synthetic man-made oils such as polysiloxane. The only animal fat that is regularly used is lanolin.

Lanolin (also known as a wool alcohol or a wool wax) is extracted from sheep’s wool. It is excreted by the sheep’s sebaceous glands and keeps the fleece soft whilst also protecting it from the elements. Historically, it has a reputation for being highly allergenic. Whilst this may have been of some concern in the past, modern extraction and purification methods mean that lanolin has a very low incidence of sensitisation and should not be considered a common allergen (Stone, 2000; British Medical Association and Royal Pharmaceutical Society of Great Britain, 2007).

There is evidence to show that lanolin is an effective emollient. This is summarised by Harris and Hoppe (2000) who report a number of studies. These suggested that lanolin:

• Reduces transepidermal water loss in xerotic skin and has long-term effects (up to 14 days after 21 days of application);
• Restores barrier function in normal skin that has been perturbed by acetone;
• Can act as a barrier to virus particles and irritants;
• Increases the rate of re-epithelisation;
• Decreases levels of skin roughness for up to 8 hours after application (Harris and Hoppe, 2000).

Lipids may be mixed with differing amounts of water to produce the various consistencies of emollient. The absolute quantity of water and the amount relative to the level of lipid present will affect the consistency and efficacy of the product. Therefore, products with high lipid content (and no water) will tend to be greasy and heavy whilst those with low lipid content (and high levels of water) will be less greasy and lighter. Most cosmetic emollients (usually lotions) have a high water content, which ensures that they sink into the skin quickly without leaving greasy traces. However they are less effective at retaining water in the skin than their greasier counterparts, creams and ointments.