Lanolin

Lanolin (German, from Latin lāna, "wool", and oleum, "oil") also called Adeps Lanae, wool wax or wool grease, is a yellow waxy substance secreted by the sebaceous glands of wool-bearing animals. Most lanolin used by humans comes from domestic sheep. Lanolin is also frequently, but incorrectly, referred to as ‘Wool Fat’ by many of the world’s pharmacopoeia even though it has been known for more than 150 years that lanolin is devoid of glycerides and is in fact a wax, not a fat. Lanolin's waterproofing property aids sheep in shedding water from their coats. Certain breeds of sheep produce large amounts of lanolin, and the extraction can be performed by squeezing the sheep's harvested wool between rollers. Most or all of the lanolin is removed from wool when it is processed into textiles, such as yarn or felt.

Lanolin’s role in nature is to protect wool and skin against the ravages of climate and the environment – it also seems to play a role in integumental hygiene. It is therefore not surprising that lanolin and its many derivatives are used extensively in products designed for the protection, treatment and beautification of human skin.

Composition

Like many natural products lanolin has a complex and variable composition. For example, a typical high purity grade of lanolin is composed predominantly of long chain waxy esters (ca. 97% by weight) the remainder being lanolin alcohols, lanolin acids and lanolin hydrocarbons.

It has been estimated that there may be between 8,000 and 20,000 different types of lanolin ester present in lanolin resulting from combinations between the ca. 200 different lanolin acids and the ca. 100 different lanolin alcohols that have so far been identified.

Lanolin’s complex composition of long chain esters, hydroxy esters, diesters, lanolin alcohols, lanolin acids means that 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 cosmetic 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 skin care products for over 100 years. Interestingly, approximately 40% of the acids derived from lanolin are alpha hydroxy acids. The use of alpha hydroxy acids (AHA’s) in skin care products has attracted a great deal of attention in recent years. Details of the AHA’s isolated from lanolin can be seen in the table below.

Type of lanolic acid	Carbon chain length	Number identified
Alpha hydroxy normal	C13 – C24	12
Alpha hydroxy iso	C13 – C23	6
Alpha hydroxy anteiso	C12 – C24	7

Modern developments

In addition to general purity requirements, there are now official requirements for the level of pesticide residues permissible in lanolin. The 5^th 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 p.p.m. (40 mg kg^-1) total pesticides was stipulated for lanolin of general use, with no individual limit greater than 10 p.p.m. (10 mg kg^-1).

A second monograph also introduced into the United States Pharmacopoeia XXII in 1992 was entitled ‘Modified Lanolin.’ Lanolin conforming to this monograph is intended for use in more exacting applications, for example on open wounds. In the Modified Lanolin monograph, the limit of total pesticides is reduced to 3 p.p.m. (3 mg kg^-1) total pesticides with no individual limit greater than 1 p.p.m. (1 mg kg^-1).

In 2000, the European Pharmacopoeia introduced pesticide residue limits into its lanolin monograph. This requirement, which is generally regarded as the new quality standard, extends the list of pesticides to 40 and imposes even lower concentration limits.

However, some very high purity grades of lanolin surpass monograph requirements. New products obtained using complex purification techniques produce lanolin esters in their natural state removing oxidative and environmental impurities resulting in white, odourless, hypoallergenic lanolin. These ultra-high purity grades of lanolin are ideally suited to the treatment of dermatological disorders such as eczema and on open wounds.

Some years ago, lanolin attracted a great deal of attention owing to a misunderstanding concerning its sensitising potential. A study carried out at New York University Hospital in the early 1950’s had shown that approximately 1% of patients with dermatological disorders were allergic to the lanolin being used at that time. However, this figure was misinterpreted and taken out of context and became quoted as 1% of the general healthy (American) population. It has been estimated that this simple misunderstanding by failing to differentiate between the general healthy population and patients with dermatological disorders exaggerates the sensitising potential of lanolin by approximately 5,000 - 6,000 times.

By the time the European Cosmetics Directive was introduced in July 1976, there had been so much adverse (but completely unfounded) publicity concerning lanolin that it contained a stipulation that cosmetics which contained lanolin should be labelled to that effect. This ruling was challenged immediately and in the early 1980’s it was overturned and removed from the Directive. Despite only being in force for a very short period of time this ruling did a great deal of harm both to the lanolin industry and to the reputation of lanolin in general. The irony is that the Cosmetics Directive ruling only applied to the presence of lanolin in cosmetic products – it did not apply to the many hundreds of different lanolin derivatives used in cosmetic products or to the use lanolin in dermatological products designed for the treatment of compromised skin conditions.

However, lanolin’s safety and efficacy is probably best illustrated taking a look at the market. High lanolin content baby care products (some as high as 100%) and treatment products for nursing mothers are commonplace.

More recently, using modern scientific methods, attention has focused on the positive aspects of lanolin and on increasing our understanding about how lanolin achieves its beneficial skin effects.

Modern analytical methods have revealed that lanolin possesses a number of important chemical and physical similarities to human stratum corneum lipids; the lipids which help regulate the rate of trans-epidermal water loss and govern the hydration state of the skin.

Cryo-scanning electron microscopy has shown that lanolin, like human stratum corneum lipids, consists of a mass of liquid crystalline material. Cross-polarised light microscopy has shown the multi-lamellar vesicles formed by lanolin are identical to those formed by human stratum corneum lipids. It is well known that the incorporation of bound water into the stratum corneum involves the formation of multi-lamellar vesicles.

Skin bio-engineering studies have shown that the durational effect of the emollient (skin smoothing) action produced by lanolin is very significant and lasts for many hours. Lanolin applied to the skin at 2mg cm^-2 has been shown to reduce roughness by ca. 35% after 1 hour and ca. 50% after 2 hours with the overall lasting for considerably more than 8 hours. Lanolin is also known to form semi-occlusive (i.e. breathable) films on the skin. When applied daily at ca. 4 mg cm^-2 for five consecutive days, the positive moisturising effects of lanolin were detectable until ca. 72 hours after final application. It has been postulated that lanolin may achieve some of its moisturising effects forming a secondary moisture reservoir within the skin.

In other studies the barrier repair properties of lanolin have been reported to be superior to those produced by both petrolatum and glycerin. In a small clinical study conducted on volunteer subjects with terribly dry (xerotic) hands, lanolin was shown to be superior to Petrolatum in reducing the signs and symptoms of dryness and scaling, cracks and abrasions, and pain and itch.8 In another study, a high purity grade of lanolin was found to be significantly superior to Petrolatum in assisting the healing of superficial wounds. Lanolin could thus be described as the definitive, natural skin barrier repair agent.

Applications

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Lanolin ointment

Lanolin and its many derivatives are used extensively in both the personal care (e.g. in high value cosmetics, facial cosmetics, lip products etc) and health care sectors. Lanolin is the cornerstone of the protective baby skin treatment (and nursing mother) markets, points which exemplify its outstanding safety and efficacy.

Lanolin is used commercially in many industrial products ranging from rust-proof coatings to lubricants. Some sailors use lanolin to create a slippery surface on their propellers and stern gear to which barnacles cannot adhere. The water-repellent properties make it valuable as a lubricant grease where corrosion would otherwise be a problem.

Lanolin is often used as a raw material for producing cholecalciferol (vitamin D₃).

Lanolin is often used by baseball players to soften and break in their baseball gloves (shaving cream that contains lanolin is popularly used for this).

Anhydrous lanolin is also used as a lubricant for brass instrument tuning slides.

Lanolin can also be restored to woolen garments to make them waterproof, such as for cloth diaper covers.

Production

Crude lanolin constitutes approximately 5-25% of the weight of freshly shorn wool. The wool from one Merino sheep will produce about 250-300 ml of recoverable wool grease. Lanolin is extracted by washing the wool in hot water with a special wool scouring detergent to remove dirt, wool grease (crude lanolin), suint (sweat salts), and anything else stuck to the wool. The wool grease is continuously removed during this washing process by centrifugal separators, which concentrate the wool grease into a wax-like substance melting at approximately 38°C (100°F).

External links

• Lanolin.com - Comprehensive view on history, manufacturing and applications
• Lanolin poisoning

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