Lanolin Refinement

The harvested wool wax is a dark, highly viscous and greasy paste. In this crude form, it can be used in several technical applications.

However, due to the colour, peculiar odour and sizeable amount of impurities it retains at this stage, the wool wax must be refined further before it can be used in cosmetic products and by the pharmaceutical industry.

Ensuring product quality

Some of the characteristics of wool wax that make it so valued actually complicate the refining process. For example, the powerful surfactant activity - one of the most highly regarded properties of refined lanolin - makes the purification process difficult.

Impurities may be retained in microscopic droplets of oil in reluctantly formed water-in-oil (w/o) emulsions, which are very difficult to break up. To counteract this, the emulsifying power of the wax has to be held to a low and controlled level during the refinement process, without impairing the product quality.

The technical process

First stages of refinement

The techniques and materials used for refining lanolin vary from processor to processor. Generally, the first step involves the break-up of soaps and removal of acid-soluble impurities by refluxing the crude wool wax in an aqueous acid solution.

Lanolin refinement is a difficult process, requiring the most state-of-the-art techniques.

After separation and disposal of the aqueous phase, the free fatty acids in the wax are neutralised via an alkaline treatment, preferably using a sodium hydroxide or carbonate solution.

The resulting soaps, which are formed by the reaction of fatty acids with alkali metal ions such as sodium, can be extracted using mixtures of ethanol or isopropanol with water.

The alcohols function both as a co-solvent and an agent to reduce the emulsifying properties of surfactant molecules. This makes sure that undesired materials are washed out of the wax mixture effectively.

Improving the purity

Depending on the desired purity grade, this extraction procedure can be repeated with more highly concentrated alcohol mixtures. A further reduction of contaminants can be achieved through treatment with adsorbents, such as activated carbon, followed by filtration.

Residual pesticides and odours can be removed by exposure to high vacuum and simultaneous heating of the wool wax. This processing step also reduces the amount of free lanolin alcohols.

By slightly varying vacuum and temperature conditions, their content can be reduced to less than 3% by weight, which is crucial if the desired result is product hypoallergenicity.

Residual pesticides, odours and impurities are removed during the refinement process.

Colour change

At this stage in the refinement process, most of the impurities - free fatty acids, detergents and pesticides - will be sufficiently reduced and the product will be pleasantly deodorised. The dark colour will have faded into a pale yellow tone.

While the colour of the refined lanolin has nothing to do with its quality, some cosmetic applications require bright lanolin. This can be achieved by bleaching the wax with common oxidative reagents such as:

hydrogen peroxide (a common ingredient in hair bleaching products)
sodium hypochlorite
sodium perborate
other inorganic materials.

If hydrogen peroxide is used, however, undesired organic peroxide derivatives of wax esters may be formed, which require additional treatment for removal.

If the lanolin is not bleached, then small concentrations of another approved antioxidant, such as butylated hydroxytoluene (BHT), are usually added at the end of the refinement process. This stops the air getting to the lanolin, preventing superficial degradation by autoxidation.

Final steps

Finally, residual water is removed through a vacuum-drying process to give refined lanolin anhydrous, a pale, ointment-like substance with a scarcely recognisable odour.

It is soluble in organic solvents like diethyl ether, chloroform and chloroform/methanol mixtures, but poorly soluble in ethanol. It does not dissolve in (but is mixable with) water, forming stable water-in-oil (w/o) emulsions.

Crude wool wax and refined lanolin compared

Comparison: crude wool wax and refined pharmaceutical lanolin (typical compositions)

Component	Crude centrifugal wool wax	Refined pharmaceutical lanolin
Water	1-5% w/w	0.05% w/w
Free fatty acids	1-8% w/w	0.30% w/w
Free fatty alcohols	6-12% w/w	2.50% w/w
Wax esters	75-90% w/w	97.0% w/w
Water soluble salts of potassium and sodium	0.1-0.2 w/w	not quantified
Lipid soluble salts of calcium, magnesium, iron, aluminium	0.2-2.0 w/w	not quantified
Detergent residues	0.1-1.0 w/w	0.02% w/w
Pesticide residues	20-150 mg kg-1	0.8 mg kg-1
Polyaromatic hydrocarbons	0.1-0.5 mg kg-1	0.08 µg kg-1
Particulate insoluble matters	0.1-2.0	not quantified
Peroxide value	not quantified	12.0 meq. kg-1
Colour	dark brown	pale to yellow
Odour	peculiar smell	almost odorless
Source: E.W. Clark 1999, 'The History and Evolution of Lanolin'

It's time to put to rest the fallacy that lanolin is an allergen

Lanolin allergy: facts and fiction

Lanolin is a well-tolerated emollient and probably one of the most marginal contact sensitisers in clinical medicine. Laboratories and clinics all over the world have studied its skin compatibility and conclude that it is not a significant allergen.

In fact, considering the widespread use of lanolin and lanolin derivatives in commercial and pharmaceutical skin-care products, the incidence of skin irritation has not increased in over a century.

Still, the myth of lanolin as an allergen persists, often in public discussion forums in which certain authorities mistakenly label it as a 'leading' sensitiser. Why is this and what is the source of this fallacy?

Roots of the myth

The answer is in the misinterpretation of a dermatological study published in 1953 by Marion Sulzberger of New York University Hospital. Sulzberger patch tested 1,048 patients suspected of contact allergy. He found that 12 individuals exhibited positive reactions to lanolin treatment, constituting a reaction rate of 1.15%.

That incidence of 1.15% was incorrectly translated to the general American population, ignoring the fact that Sulzberger's test patients, as he detailed in his study, belonged to a group "predisposed to acquire multiple specific sensitisations of the skin to eczematous allergens".

In other words, his test group was prone to skin allergies. In a control group of 120 healthy test subjects, none experienced any reaction to lanolin.

Applicable for hypoallergenic formulations

Most researchers conclude that the incidence of lanolin allergy within the general population is negligibly low, varying from approximately 10 to 1 per million. Incidence can be lowered practically to zero when the content of free lanolin alcohols is reduced to a share of 3% or less.

This purified lanolin causes still fewer reactions, even among patients known to be lanolin sensitive, and fulfils the requirements for use in hypoallergenic formulations. Scientists believe that components of the alcoholic fraction are responsible for the small number of sensitisations, although the exact component has not yet been identified.

Renowned skin researcher Albert M. Kligman, from the Philadelphia School of Medicine, says: "It is time to stop denigrating a wonderful natural substance, which has been used for thousands of years as a luscious emollient and an all-purpose vehicle for a great variety of skin-care products."