PARAFFINS

Hard, soft and liquid paraffins are mixtures of hydrocarbons obtained from petroleum. Soft and liquid paraffins can be used on their own as emollients and are effective occlusive agents.

However, they are not usually cosmetically acceptable as they are greasy and difficult to wash off. And their occlusive effects can sometimes lead to skin maceration, which may aggravate existing dermatitis. Mixtures of hard, soft and liquid paraffins are used as bases in many emollient and other dermatological creams.

GLYCEROL, PROPYLENE GLYCOL

Glycerol is a trihydric alcohol; it is hygroscopic and is included in emollient and hydrating products to promote water retention in the skin. It also improves the feel and consistency of formulations, making them more pleasant to use. Propylene glycol has hygroscopic properties similar to glycerol and is used in emollients to increase skin hydration.

UREA

At a concentration of 10 per cent, urea increases skin hydration (at higher concentrations it is claimed to have keratolytic and antipruritic properties). Urea can cause burning or stinging, and may irritate inflamed skin, but this is usually minimised by formulating products to a pH of six.