One of the principal reasons for use of a lipid material in cosmetics is its emol­liency. The term »emollient« is of Latin origin meaning a material capable of smoothening dry and wrinkled skins and maintaining these conditions for a certain period of time. Water alone is capable of exhibiting such effects but the effects are short lived due to its quick evaporation.

Presence of essential fatty acids (EFA) like, linoleic acid (n-6), u-linolenic acid (n-3), y-linolenic acid (n-6) in the oils is often an important criterion for selec­tion. Effect of such EFA’s on human physiological systems through oral in­take is well documented. They also con­tribute to beneficial physiological activ­ities when applied topically through creams or lotions.
Both natural oils and exotic butters are widely used in cosmetic products and neutraceuticals. Evening primrose oil (EPO) (Oenothera biennis) and bor­age oil (Borago officinalis) are very com­mon natural oils, used primarily be­cause of their high content of gamma linolenic acid. Evening primrose oil and borage oil contains about 9-11 % and 18-23 % of gamma linolenic acid respectively. Use of oils with high amount of polyunsaturated fatty acids like camelina oil (Camelina sativa), blackcurrant seed oil (Ribes nigrum) and flax seed oil (Unum Usitatissimum) for cosmetic applications are also preva­lent. Usually obtained from tropical jungle crops, exotic butters like shea (Butyrospermum Parki), mango (Man· gifera indica), sal (Shorea robusta) are among the commonly used exotic but­ters for skin care products. They are rich in symmetrical monounsaturated triglycerides which are solid or semi­solid at room temperature. They have narrow melting points and have ap­preciable viscosity and emulsion sta­bility. The exotic butters are also rich in unsaponifiables such as sterols, ubiquinones, fatty alcohols, fatty es­ters, triterpines etc. Application of natural oils and butters in various cos­metic formulations is a great challenge in combating oxidation.

Oxidation of oils and fats

The oil or fat content of a cosmetic product can vary from 2-15 % in case of body lotions and creams while it can be 100 % in case of massage oils. It is very important that only the best quali­ty oil or fat is used in any cosmetic for­mulation »Quality« of a commercial oil

or fat is very often measured through its oxidative stability. Oxidation of a lipid is a very common and serious problem for any fat containing prod­uct, food or cosmetic. Characteristic changes linked with oxidative degradation of oils and fats include devel­opment of malodors, unpleasant tastes and might lead to change of colour, in­crease in viscosity, specific gravity and solubility. The mechanism of autoxida­tion has postulated by many authors. Autoxidation is a natural free radical process between molecular oxygen and the unsaturated fatty acids of an oil which leads to the for­mation of short lived hydroperoxides (primary oxidation products). The hy­droproxides readily break down to form alcohols, aldehydes, ketones and other hydrocarbnons. These secondary oxidation products impart rancid odor and taste. One way of preventing au­toxidation is addition of antioxidants. The interest of the food and cosmetic industry in phenolic antioxidants is pri­marily related to the extension of the shelf life of the various consumer products. In the present global mar­ket, there is hardly any food or cos­metic product, semi-finished or fin­ished, which does not contain any added preservatives. The antioxidants used are mostly synthetic, namely butylated hydroxytoluene (BHT), buty­lated hydroxyanisole (BHA}, ascorbyl paImitate, tertiary butylhydroxyquinone (TBHQ) etc. But the consumers’ aware­ness of the possible toxic side effects of synthetic antioxidants and preference for natural additives, has led to more detailed investigations and applica­tions of natural herb extracts as anti­oxidants.

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