Page 96 -- SKIN CARE

Skin cleansing The aim of cleansing is to remove: surface dirt all make-up the top layer of dead skin cells potentially harmful micro-organisms (bacteria). The way in which any individual chooses to carry out this process is determined by habit, skin feel requirements and activity. What goes to make a cleansing product? For many generations soaps have been made by the extraction of oils and tallows from plants and animals and then treating these with alkalis to neutralise the fatty acids they contain. Soaps are good emulsifiers (that is, they hold solids and oils in liquids in emulsion form so that they can be rinsed away), they have reasonable lathering power and an emollient action. Unfortunately, two problems are associated with soaps.     Firstly, because of their powerful cleansing action, overuse may completely eliminate the protective lipid film on the skin surface, which helps maintain the skin's physiological balance. As a result they may give rise to irritation.     Secondly, some soaps are alkaline (they have a high pH, around 9). Since skin pH is about 5, washing with soap leads to pH increases on the skin that can last for up to two hours.     'Oily' soaps are enriched with emollients such as glycerol, fatty acids or oils, which have a softening and smoothing action. They can leave the skin softer than ordinary soap does by avoiding excessive removal of lipids from the skin surface, but they suffer from the same pH problem.     Most hygiene products contain ingredients called surfactants (or sometimes detergents). The terms include a wide range of substances, all of which are effective to a greater or lesser degree in dispersing greasy materials in water. Scientists call these greasy materials hydrophobic, from the Greek words meaning 'water-hating' because oils will not mix with water unless

'helped' by a surfactant. Soaps are surfactants, strictly speaking, but the term is usually kept specifically for man-made (synthetic) surfactants.     Surfactants are found in laundry detergents, liquid cleansers, shampoos and shower products. Their chemistry makes it possible for them to remove soiling from many different materials, including skin and hair, so that oil and grime can be rinsed away. Some surfactants are harsh to the skin while others are very mild, depending on their type. Based on this wide variety of available surfactants, not all cleansers ar the same. It is important to use products that best fit your skin type.     Surfactants are classified according to their structure: cationic surfactants (ammonium compounds): these are poorly tolerated by most people's skins, and are now hardly used at all in skin care products anionic surfactants such as sodium lauryl sulphate - their molecules have a negatively charged 'head' and a long hydrophobic 'tail'; these are widely used because of their good lathering and detergent properties amphoteric surfactants such as the betaines, and alkylamino acids - these are well tolerated and lather well, and are used in shampoos non-ionic surfactants such as sucrose esters - overall these molecules are uncharged; these are tolerated better than other types, but do not lather particularly well. Syndets (short for 'synthetic detergents') are mixtures of synthetic surfactants, mainly anionic surfactants with some added amphoteric surfactants to improve their tolerability. Their potential lies in the fact that their pH may be adjusted to that of skin, and they can be enriched with oily compounds.     To best maintain the skin surface's physiological balance, it may be better to use syndets rather than soaps for all personal cleansing. This is especially true for young children, whose skin is more delicate than adult skin. It is also true for the sensitive skin of the scalp, for which the best care centres on the use of a mild shampoo formulated for frequent use.