Lanolin

Lanolin (from Latin lāna ‘wool’, and oleum ‘oil’), also called wool yolk, wool wax, or wool grease, is a wax secreted by the sebaceous glands of wool-bearing animals. Lanolin used by humans comes from domestic sheep breeds that are raised specifically for their wool. Historically, many pharmacopoeias have referred to lanolin as wool fat (adeps lanae); however, as lanolin lacks glycerides (glycerol esters), it is not a true fat. Lanolin primarily consists of sterol esters instead. Lanolin's waterproofing property aids sheep in shedding water from their coats. Certain breeds of sheep produce large amounts of lanolin. Lanolin's role in nature is to protect wool and skin from climate and the environment; it also plays a role in skin (integumental) hygiene. Lanolin and its derivatives are used in the protection, treatment and beautification of human skin. A typical high-purity grade of lanolin is composed predominantly of long chain waxy esters (approximately 97% by weight) the remainder being lanolin alcohols, lanolin acids and lanolin hydrocarbons. An estimated 8,000 to 20,000 different types of lanolin esters are present in lanolin, resulting from combinations between the 200 or so different lanolin acids and the 100 or so different lanolin alcohols identified so far. Lanolin’s complex composition of long-chain esters, hydroxyesters, diesters, lanolin alcohols, and lanolin acids means in addition to it being a valuable product in its own right, it is also the starting point for the production of a whole spectrum of lanolin derivatives, which possess wide-ranging chemical and physical properties. The main derivatisation routes include hydrolysis, fractional solvent crystallisation, esterification, hydrogenation, alkoxylation and quaternisation. Lanolin derivatives obtained from these processes are used widely in both high-value cosmetics and skin treatment products. Hydrolysis of lanolin yields lanolin alcohols and lanolin acids. Lanolin alcohols are a rich source of cholesterol (an important skin lipid) and are powerful water-in-oil emulsifiers; they have been used extensively in skincare products for over 100 years. Notably, approximately 40% of the acids derived from lanolin are alpha-hydroxy acids (AHAs). The use of AHAs in skin care products has attracted a great deal of attention in recent years. Details of the AHAs isolated from lanolin can be seen in the table below. In addition to general purity requirements, lanolin must meet official requirements for the permissible levels of pesticide residues. The Fifth Supplement of the United States Pharmacopoeia XXII published in 1992 was the first to specify limits for 34 named pesticides. A total limit of 40 ppm (i.e. 40 mg/kg) total pesticides was stipulated for lanolin of general use, with no individual limit greater than 10 ppm.