Hypersensitivity to Lanolin: An Old-New Problem.

Lanolin is a fatty substance derived from sheep's fleece. The ancient Greeks used the moisturizing and skin-protective properties of this substance. The technique of industrial production of lanolin was developed in Germany in the 19th century. Since then, this natural wax has become an extremely popular base for many different cosmetic and pharmaceutical preparations intended for the treatment and care of the skin. In addition to its medicinal and cosmetic applications, lanolin is also widely used for industrial purposes. Hypersensitivity to lanolin has raised many questions and controversies for almost 100 years. Although lanolin has significant dermoprotective properties and when applied to intact skin without inflammatory changes, it lubricates it, improves its lipid barrier, and maintains proper moisture, it can also cause contact hypersensitivity when in contact with pathologically changed or damaged skin. It can, in the same person, both protect and damage the skin, depending on the condition of the skin to which the cosmetic or medicine containing lanolin is applied. The nature of the observed reactions and the circumstances of their occurrence, as well as the lack of a clear answer to the question of whether this wax causes allergies or not, make this phenomenon one of the so-called dermatological paradoxes. Although unusual reactions to lanolin have been the subject of research for many years, they still raise many questions to which there is still no clear answer. This is mainly due to the imperfection and incompleteness of the available publications. Although many different studies have been published on hypersensitivity to lanolin, most of them are retrospective analyses of the results of routinely performed epidermal patch tests or descriptions of clinical cases. Such reports and analyses, although undoubtedly very important, are a poor tool for assessing the sensitizing potential of lanolin and/or its derivatives. It is difficult to determine the causative factors, to define lanolin allergens, to investigate immunological mechanisms, or to assess the clinical significance of this phenomenon. There is a definite lack of standardized studies on the nature of lanolin hypersensitivity involving well-selected groups of patients and healthy volunteers, which would be conducted in a reproducible manner under laboratory and/or clinical conditions. As of today, lanolin hypersensitivity seems to be both an old and new problem that still remains unresolved.