Virtually everyone is aware of the connection between dietary cholesterol and heart disease. But it may come as a surprise that cholesterol is often used as an ingredient in cosmetics. Why is it used in this fashion and why is there concern about adding it to such products?
Many cosmetics, ranging from lipstick to moisturizing creams, contain ingredients referred to as emollients. Their main purpose is to keep moisture in the skin from evaporating. It is the loss of water that reduces the suppleness and smoothness of skin and leads to a dry, scaly texture. Emollients are chemicals that coat the skin and prevent moisture from passing through. Oils are very effective emollients but their slippery feel is undesirable. In general, the challenge is to find substances that prevent moisture loss but do not make the wearer feel like a greaseball. Cholesterol meets this challenge. It is readily absorbed into the surface of the skin and serves as a very effective emollient without feeling oily. Now for the concern. Cholesterol is found only in animals and therefore all sources are animal derived. Extraction from the spinal cords of cattle or from lanolin, the natural grease found on wool, is the most common route to commercial cholesterol. These days there is concern about any product derived from animals, particularly cow brains and spinal cords, because of the possible transmission of bovine spongiform encephalopathy (BSE), better known as “mad cow disease.” The prevailing opinion is that this problem was originally caused by feeding animal products, including those derived from sheep, to cattle. When cholesterol is extracted from spinal cords or wool, there is always the chance of contamination with trace amounts of other animal products, perhaps even the special proteins known as “prions” which have been implicated in BSE. The risk of anybody contracting mad cow disease from cosmetics borders on zero, but cosmetic producers have to contend with the perception among consumers that the inclusion of any animal product is undesirable. This is the reason that manufacturers are looking toward non-animal sources of cholesterol. Chemists at Sigma-Aldrich have developed a process to synthesize cholesterol from plant sources. Some plants, such as the Mexican yam, are excellent sources of steroids which through a sequence of chemical reactions can be converted into cholesterol. This cholesterol can be used in cosmetics as well as by researchers who use cholesterol because of its growth promoting properties in cell culture, an important feature in pharmaceutical research. The development of a synthetic process to produce cholesterol from raw materials in plants is another example of problem solving through the appropriate use of chemistry.