Terminology of topical skin preparations
Antipruritic agent One that relieves itching.
Base or vehicle A mixture of powders, water and greases (usually obtained from petroleum). The relative blending of these compounds determines the nature of the base (e.g. lotion, cream, ointment, gel or paste).
Cream A suspension of a powder in an emulsion of oil and water with the addition of an emulsifying agent. Usually applied to normal or moist skin.
Emollient A topical preparation of emulsified oils and fatty acids that is softening or soothing to the skin. It replaces natural oils in the stratum corneum. It also acts as a skin moisturiser and is therefore used on dry skin or dermatoses related to dry skin (e.g. atopic dermatitis). Examples are:
Emulsion A mixture of two immiscible liquids, one being dispersed throughout the other in small droplets.
Gel A viscous substance with a greaseless, water-miscible base.
Humectant A chemical-containing agent that attracts and retains water due to its hygroscopic or osmotic properties. Examples are:
urea 10% cream
glycerol 10% cream
Keratolytic An agent that softens or breaks up keratin. Examples are:
urea 10%—for xerosis or keratosis pilaris
urea 20%—cracked palms and soles
salicylic acid 2–10%
alpha-hydroxy acids (e.g. lactic acid, propylene glycol)
Lotion A suspension of an insoluble powder in water. Modern lotions use an emulsifying agent, which eliminates the need to shake the lotion. An example is calamine lotion (zinc oxide 5, calamine 15, glycerine 5, water to 100).
Moisturiser An agent that increases the water content of the stratum corneum and reduces itching. Classified as:
Ointment A suspension of a substance in an oily vehicle. Generally used for dry scaly skin.
Paint and tincture A rapidly drying liquid preparation that is very useful for intertriginous areas, especially between the toes and in the natal cleft. ‘Tincture’ is the preparation when alcohol is the vehicle. Example: podophyllin in tinct. benz. co. (for genital warts).
Paste Similar to ointment in composition but is more viscid. A paste consists of an ointment to which another agent, such as starch, has been added. They dry and protect.
The relative clinical potency of topical corticosteroids is given in TABLE 119.8.