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Background: Diagnosis of contact allergy (CA) to Amerchol L-101 (AL-101), a marker for lanolin allergy, is problematic. Positive patch test reactions are frequently doubtful or weakly positive and difficult to associate with clinical relevance., Objective: To gain further insight on the allergic or irritant nature of skin reactions induced by AL-101 patch test., Methods: We re-tested in a dose-response fashion, 10 subjects with AL-101 CA and performed comprehensive transcriptomic analysis (gene arrays, quantitative real-time polymerase chain reaction [qRT-PCR]) of samples of their skin reactions., Results: Eight of the 10 CA subjects reacted positively upon re-test, whereas two did not react. Most of AL-101 positive patch tests expressed an allergy signature with strong activation of gene modules associated with adaptive immunity and downregulation of cornification pathway genes. In addition, the breadth of gene modulation correlated with the magnitude of patch test reactions and the concentration of AL-101 applied. However, we observed that some of the positive patch test reactions to AL-101 expressed no/few allergy biomarkers, suggesting the induction of an irritant skin inflammation in these samples., Conclusions: This study confirms that AL-101 is an allergen that can cause both contact allergy and contact irritation. Our results also highlight that molecular profiling might help to strengthen clinical diagnosis., (© 2022 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: There is controversy as to whether coumarin, an ingredient in cosmetics and fragrances, is a contact allergen involved in fragrance allergy. We recently showed that the purity of coumarin is a critical parameter for its allergenicity because coumarin preparations containing trace amounts of contaminants induced cell proliferation in the local lymph node (LN) assay whereas pure coumarin did not., Objective/method: In the present study, we analyzed the sensitizing properties of coumarin (purity > 99.9) and of dihydrocoumarin (DHC), in a recently developed model of fragrance allergy in mice., Results: DHC was able to prime T cells in LNs draining the sensitization skin site and to induce a typical allergic contact dermatitis (ACD) reaction upon challenge, confirming that DHC is endowed with moderate sensitizing properties. In contrast, no T-cell activation and no ACD responses were obtained following sensitization and challenge with coumarin., Conclusion: These results confirm that pure coumarin is endowed with very weak sensitizing capacities, if any, and suggest that the presence of contaminants in coumarin preparations may account for the previously reported allergenic properties of coumarin.