SPECIFIC LANOLIN ALLERGY 325 Lanolin, in the common usage of the term, should more correctly be referred to as 'Anhydrous lanolin', synonyms being Wool Fat, Wool Wax or the Latin name Adeps Lanae. It originates as a natural, unique type of wax secreted by sebaceous glands in the skin of sheep, and its refining in- volves the removal of adventitious and natural impurities without signifi- cantly affecting the essential substance. In composition it is predominantly a complex mixture of esters of high molecular weight alcohols and fatty acids (13), and these esters can be hydrolysed to yield separate alcoholic and acidic fractions both of which are themselves complex mixtures. The alcoholic fraction, like the parent lanolin, is widely used in products for skin care again under a variety of names: Wool Alcohols, Wool Wax Alcohols, Lanolin Alcohols, Alcoholia Lanae, and so on. EXPOSURE TO LANOLIN Previous authors have noted that small amounts of unrefined wool wax can be present in wool clothing, since the wool textile industry deliberately aims to leave a small residue of the wax in wool in order to retain its softness to the touch. For example, the standard allowance in the industry for the residual grease (wool wax) content of dry-combed wool tops supplied to spinners is 0.634•o, as high as the lanolin content of many cosmetics. Most people may thus be expected to be in frequent and prolonged contact with wool wax, irrespective of whether they use lanolin-containing products on their skin or not. A few cases of allergic sensitization to wool have been recorded in the literature (8), (14), (15), in one of these a cure was claimed following a desensitizing treatment with an extract of wool. In addition to wool and preparations intended for use on the skin, many other commodities also contain lanolin, wool wax or lanolin alcohols, a few examples being shoe polishes, floor waxes, paper, printing ink, man- made textile finishes, fur dressings and leather dressings (16). Thus, most members of the public in developed countries may be expected to be in frequent contact with lanolin or wool wax from one source or another, and this very extensive exposure must be considered in arriving at any estimate of allergic incidence in general. LIMITATIONS OF TEST METHODS The results of investigations so far published contain uncertainties and

326 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS exaggerations inherent in the stringent test methods which have been forced on investigators by the difficulty of the problem. The underlying difficulty is that the allergic response to lanolin is so weak that results from even the 100•o substance are unreliable, (9), (10), (17), (18), (19), whilst diluting lanolin with an inert vehicle further increases the chance of false negative results (12). Attempting to circumvent these difficulties, many workers, especially the more recent, have employed two modified types of test, now designated (a) and (b): (a) In the first modification an addition of 2-5•o of salicylic acid or 2•o of resorcin, to quote but two examples, is made to lanolin in order to act as a keratolytic and increase the penetration of any allergens through the epidermis. The weakness of this method is that salicylic acid can itself, as is well documented, provoke an allergic response or even primary irritation. Hence sometimes, but not always, the precaution has been taken of testing subjects both with the lanolin mixture and with salicylic acid in petroleum jelly, only cases of positive reaction to the former with negative reaction to the latter having been regarded as significant. This qualification is inade- quate, however, since it is known that a mixture of substances, each in- nocuous on its own, may exhibit synergism or in some other way induce a false positive result (20). For example the occurrence of false positive results from lanolin with added keratolytic was experienced and reported by Cronin (19), whilst the method has been criticized also by Thune (2) and by Fisher (8). Bonnevie (21) queried whether his positive reaction to 5•o salicylic acid in lanolin was perhaps a secondary irritation from salicylic acid. Present opinion is almost unanimous that a test modification of this type invokes a large degree of exaggeration, and this point is discussed later in more detail. (b) As a second modification, tests are made not with lanolin itself but with a solution of lanolin alcohols in petroleum jelly, usually at 30• con- centration although some workers have used 6•o ('eucerin') or intermediate levels. In all cases this method has elicited an increased incidence of positive reactions compared to the use of lO0•o lanolin, and again there is a funda- mental weakness since the method assumes a similarity in dermatological effect between esters on the one hand and alcohols on the other, whereas there is a distinct chemical difference between the two. Moreover, due to the relatively severe processing conditions needed to hydrolyse lanolin esters, it is possible that commercial lanolin alcohols contain degradation