Lanolin Controversies
The allergenicity of lanolin is far from straightforward. In 1996, Wolf17 first described the “lanolin paradox,” modeled after the earlier “paraben paradox” described by Fisher.18 There are 4 clinical phenomena of the lanolin paradox17:
- Lanolin generally does not cause contact allergy when found in PCPs but may cause ACD when found in topical medicaments.
- Some patients can use lanolin-containing PCPs on healthy skin without issue but will develop ACD when a lanolin-containing topical medicament is applied to inflamed skin. This is because inflamed skin is more easily sensitized.
- False-negative patch test reactions to pure lanolin may occur. Since Wolf’s17 initial description of the paradox, free alcohols of lanolin have been found to be its principal allergen, though it also is possible that oxidation of lanolin could generate additional allergenic substances.1
- Patch testing with wool alcohol 30% can generate both false-negative and false-positive results.
At one extreme, Kligman19 also was concerned about false-positive reactions to lanolin, describing lanolin allergy as a myth attributed to overzealous patch testing and a failure to appreciate the limitations of this diagnostic modality. Indeed, just having a PPT to lanolin (ie, contact allergy) does not automatically translate to a relevant ACD,1 and determining the clinical relevance of a PPT is of utmost importance. In 2001, Wakelin et al20 reported that the majority (71% [92/130]) of positive reactions to Amerchol L101 50% or 100% pet showed current clinical relevance. Data from the North American Contact Dermatitis Group in 2009 and in 2022 were similar, with 83.4% (529/634) of positive reactions to lanolin alcohol 30% pet and 86.5% (1238/1431) of positive reactions to Amerchol L101 50% pet classified as current clinical relevance.11,21 These findings demonstrate that although lanolin may be a weak sensitizer, a PPT usually represents a highly relevant cause of dermatitis.
Considerations for Patch Testing
Considering Wolf’s17 claim that even pure lanolin is not an appropriate formulation to use for patch testing due to the risk for inaccurate results, you might now be wondering which preparation should be used. Mortensen22 popularized another compound, Amerchol L101, in 1979. In this small study of 60 patients with a PPT to lanolin and/or its derivatives, the highest proportion (37% [22/60]) were positive to Amerchol L101 but negative to wool alcohol 30%, suggesting the need to test to more than one preparation simultaneously.22 In a larger study by Miest et al,23 3.9% (11/268) of patients had a PPT to Amerchol L101 50% pet, whereas only 1.1% (3/268) had a PPT to lanolin alcohol 30% pet. This highlighted the importance of including Amerchol L101 when patch testing because it was thought to capture more positive results; however, some studies suggest that Amerchol L101 is not superior at predicting lanolin contact allergy vs lanolin alcohol 30% pet. The risk for an irritant reaction when patch testing with Amerchol L101 should be considered due to its mineral oil component.24
Although there is no universal consensus to date, some investigators suggest patch testing both lanolin alcohol 30% pet and Amerchol L101 50% pet simultaneously.1 The TRUE test utilizes 1000 µg/cm2 of wool alcohols, while the North American 80 Comprehensive Series and the American Contact Dermatitis Society Core 90 Series contain Amerchol L101 50% pet. Patch testing to the most allergenic component of lanolin—the free fatty alcohols (particularly alkane-α,β-diols and alkane-α,ω-diols)—has been suggested,1 though these formulations are not yet commercially available.
When available, the patient’s own lanolin-containing PCPs should be tested.1 Performing a repeat open application test (ROAT) to a lanolin-containing product also may be highly useful to distinguish weak-positive from irritant patch test reactions and to determine if sensitized patients can tolerate lanolin-containing products on intact skin. To complete a ROAT, a patient should apply the suspected leave-on product to a patch of unaffected skin (classically the volar forearm) twice daily for at least 10 days.25 If the application site is clear after 10 days, the patient is unlikely to have ACD to the product in question. Compared to patch testing, ROAT more accurately mimics a true use situation, which is particularly important for lanolin given its tendency to preferentially impact damaged or inflamed skin while sparing healthy skin.
Alternatives to Lanolin
Patients with confirmed ACD to lanolin may use plain petrolatum, a safe and inexpensive substitute with equivalent moisturizing efficacy. It can reduce transepidermal water loss by more than 98%,4 with essentially no risk for ACD. Humectants such as glycerin, sorbitol, and α-hydroxy acids also have moisturizing properties akin to those of lanolin. In addition, some oils may provide benefit to patients with chronic skin conditions. Sunflower seed oil and extra virgin coconut oil have anti-inflammatory, antibacterial, and barrier repair properties.26,27 Allergic contact dermatitis to these oils rarely, if ever, occurs.28
Final Interpretation
Lanolin is a well-known yet controversial contact allergen that is widely used in PCPs, cosmetics, topical medicaments, and industrial goods. Lanolin ACD preferentially impacts patients with stasis dermatitis, chronic leg ulcers, AD, and perianal/genital dermatitis. Patch testing with more than one lanolin formulation, including lanolin alcohol 30% pet and/or Amerchol L101 50% pet, as well as testing the patient’s own products may be necessary to confirm the diagnosis. In cases of ACD to lanolin, an alternative agent, such as plain petrolatum, may be used.