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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: Skin exposure to chemicals may induce an inflammatory disease known as contact dermatitis (CD). Distinguishing the allergic and irritant forms of CD often proves challenging in the clinic., Methods: To characterize the molecular signatures of chemical-induced skin inflammation, we conducted a comprehensive transcriptomic analysis on the skin lesions of 47 patients with positive patch tests to reference contact allergens and nonallergenic irritants., Results: A clear segregation was observed between allergen- and irritant-induced gene profiles. Distinct modules pertaining to the epidermal compartment, metabolism, and proliferation were induced by both contact allergens and irritants; whereas only contact allergens prompted strong activation of adaptive immunity, notably of cytotoxic T-cell responses. Our results also confirmed that: (a) unique pathways characterize allergen- and irritant-induced dermatitis; (b) the intensity of the clinical reaction correlates with the magnitude of immune activation. Finally, using a machine-learning approach, we identified and validated several minimal combinations of biomarkers to distinguish contact allergy from irritation., Conclusion: These results highlight the value of molecular profiling of chemical-induced skin inflammation for improving the diagnosis of allergic versus irritant contact dermatitis., (© 2021 EAACI and John Wiley and Sons A/S. Published by John Wiley and Sons Ltd.)