The woolly culprit: Lanolin revealed as an uncommon cause of dermatitis on normal skin
By Christen Mowad, MD, FAAD
Nov. 15, 2023
Vol. 5, No. 46
Excitement surrounding the “Allergen of the Year” may only be truly appreciated by those immersed in the field of contact dermatitis and patch testing, but each year the announcement is met with enthusiasm from the wider dermatology specialty. The Allergen of the Year is used by the contact dermatitis world to highlight allergens that may be new or emerging; sometimes this announcement highlights allergens that get significant attention but are not substantial clinical problems in terms of allergenicity. The 2023 allergen of the year is lanolin. (1)
Lanolin is used primarily for its emollient properties and is found in many personal care products; it is also used in the industrial arena. As such, it can be seen as an allergen in allergic contact dermatitis to personal care products and in occupational contact dermatitis cases, respectively. Lanolin is a complex mixture derived from secretions of the sebaceous glands of sheep. It contains high molecular weight esters, aliphatic alcohols, sterols, fatty acids, and hydrocarbons. (1,2,3) Its components and allergenicity depend in part on the breed of sheep, geographic location as well as the processing method and level of purification. (2,3) The allergenic components of lanolin are felt to be the free lanolin alcohols. (1,2,3) Purification does impact the allergenicity of a lanolin product with medical grade lanolin and highly purified medical grade lanolin having less allergenicity. (1)
The most appropriate lanolin concentration to use when patch testing for lanolin allergy has been debated over time. (1) The North American Contact Dermatitis Group (NACDG) has used lanolin alcohol 30% and more recently Amerchol L101 50% in petrolatum. (3,4) The NACDG study of their group experience over 17 years from 2001-2018 found lanolin sensitivity to be common, relevant, and typically linked to personal care products. (3) The distribution was most common on the hands, followed by a scattered distribution and then the face. (3) Lanolin allergy was also more common in children in their study. (3) The most recent NACDG cycle data from 2019-2020 used Lanolin alcohol (Amerchol L101) 50% petrolatum and found 3.7% of their patients had a positive reaction; lanolin was the 18th most common allergen in their most recent cycle. (4)
Certain populations may have a higher incidence of lanolin allergy, including those with compromised skin such as those with stasis dermatitis, chronic leg ulcers, or those with perianal and genital dermatitis. (1) Children, due to atopic dermatitis, and the elderly, due to stasis dermatitis, more commonly have lanolin allergy. (1)
The lanolin paradox, a term coined by Dr. Ronni Wolf, describes those that patch test positive to lanolin but can tolerate this allergen on normal skin. (1,2,5) It is felt that individuals may become sensitized to lanolin through products used on compromised skin. These same patients do not have problems when using the lanolin-containing product on normal skin. (1,2,5) The repeat open application test (ROAT) can often help direct the use of lanolin-containing products in those that patch test positive to lanolin. (1)
Patch testing materials have been debated over the years and are often either lanolin alcohols 30% or Amerchol-L101 (50%). False negative patch tests on normal skin, even when patients are sensitized through damaged skin, can be challenging. The ROAT test helps determine if patch test positive patients can use lanolin on normal skin. (1) Lastly, lanolin patch test positivity does not mean that wool clothing is off the table for patients deemed allergic to lanolin, as wool textiles do not contain lanolin though patients may still be irritated by coarse wool fibers. (1)
Point to Remember: Lanolin is the 2023 Allergen of the Year and is present in many personal care and industrial products. For those who have a positive patch test to lanolin, it is important to remember the “lanolin paradox” where patients have a positive patch test but tolerate lanolin on normal skin.
Our expert’s viewpoint
Bruce A. Brod, MD, MHCI, FAAD
Associate Dean of Continuing Medical Education
Clinical Professor of Dermatology
University of Pennsylvania Perelman School of Medicine
Lanolin is a highly complex mixture of esters, di-esters, and hydroxyl esters of high molecular weight lanolin alcohols and high molecular weight lanolin acids. The name is derived from Latin meaning lana (wool) and oleum (oil). Lanolin, also called wool grease, may constitute 5% to 25% of the weight of sheared wool, so it’s a major component of wool and makes for a great emollient. It is important, however, not to confuse wool fiber intolerance among patients with atopic dermatitis, with lanolin hypersensitivity being more prevalent among atopic patients. The two are unrelated. Certain Merino wool fabrics, produced using modern textile manufacturing techniques, are well tolerated by atopic patients and sometimes provide better tolerance than our default recommendation of cotton and silk. (6)
The reason lanolin is used in personal care products is due to its unique tenacity for the skin making it ideal for skin creams and lipsticks. It makes for a very good emollient because of its excellent water holding capacity. The composition varies based on the breed of sheep, geographic location, method of extraction, and level of purification. (7) While this variability has led to uncertainty about the relevance of lanolin to allergic contact dermatitis, we can make a few firm conclusions based on the evidence.
If you’ve seen one type of lanolin, you’ve seen one type of lanolin. Lanolin is highly variable in its composition due to many factors.
Lanolin is a cause for allergic contact dermatitis more commonly in children, patients with atopic dermatitis, and in conjunction with certain skin conditions including stasis dermatitis, ulcers, and pre-existing dermatitis.
Applying personal care products containing lanolin on normal skin does not pose much risk for allergic contact dermatitis even in patients who test positive to lanolin or Amerchol L 101. This is the lanolin paradox and has been recognized as a phenomenon for several decades.
The alcoholic fraction of lanolin is responsible for most of the allergic contact dermatitis, although one specific allergen has not yet been identified.
Lanolin alcohol or Amerchol L 101 is generally a weak sensitizer.
Along the way we have been socialized through our medical literature to shy away from lanolin or wool wax alcohol because of its potential allergenicity. Likely this is why industry is incorporating less lanolin into personal care products which may account for the slight decrease in positive patch test reactions. Emollients in general are very therapeutic for skin conditions associated with barrier dysfunction. Emollients create a thin layer on the skin to prevent water evaporation and maintain the skin’s flexibility. The ideal emollients are sebum and lipid. Analytical chemistry has revealed that lanolin has several important chemical and physical features like the lipids in human stratum corneum, so it is no wonder that it is incorporated into products used to preserve the skin barrier. (8)
As a dermatologist specializing in contact dermatitis, I frequently encounter challenges with weak positive patch test reactions, which make it difficult to counsel patients about the significance of the reaction in terms of avoidance or its role in their existing dermatitis. Patch testing, our gold standard for diagnosing allergic contact dermatitis, is flawed because it often fails to confidently differentiate between allergic and irritant reactions. In my practice, Amerchol L 101, which is de facto lanolin, is a common culprit that contributes to this dilemma. Ideally, we would have a reliable method to distinguish between irritant and allergic reactions during patch testing. A small study conducted in 2022 measured the expression of allergic marker genes and found that most patients with positive patch test reactions to Amerchol L 101 exhibited gene expression indicative of allergy, and the strength of the patch test correlated with the level of gene expression. (9) However, a few patch test reactions did not display allergic gene expression. From this study, I conclude that Amerchol L 101 allergy is indeed real, but false positive reactions should be considered. While I will still refrain from overconfidently diagnosing allergic contact dermatitis to Amerchol L 101 based solely on a positive patch test, I will feel more justified in maintaining a healthy degree of uncertainty.
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Silic LL, LeFevre MA, Bergendorff O. Gene profiling reveals a contact allergy signature in post positive Amerchol L-101 patch test reactions. Contact Dermatitis 2022; 87:40-52.
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