Unique molecular signatures typify skin inflammation induced by chemical allergens and irritants.

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.

Octocrylene, an emerging photoallergen.

BACKGROUND: Octocrylene is a new emerging photoallergen. We report and discuss 50 cases of photoallergic contact dermatitis from octocrylene use and/or positive photopatch test reactions to this UV filter and draw attention to the unexpected association in adults with a history of photoallergic contact dermatitis from ketoprofen. OBSERVATIONS: Patients were divided in 3 groups: group A comprised 11 children; group B, 28 adults with a history of photoallergy from sunscreen products; and group C, 14 adults systematically tested with octocrylene because of a history of photoallergy from ketoprofen. All patients but 3 in group C had positive test reactions to octocrylene. Ten of 11 children in group A and 9 of 28 adults in group B had positive patch test reactions to octocrylene. One child in group A, the other 19 adults in group B, and 11 of 14 adults in group C had positive photopatch test reactions to octocrylene. All adults in group C and 24 of 28 adults in group B had a history of photoallergy from ketoprofen and positive patch test or photopatch test reactions to other allergens that are often positive in patients with photoallergy from ketoprofen, especially fragrance components. CONCLUSIONS: Octocrylene appears to be a strong allergen leading to contact dermatitis in children and mostly photoallergic contact dermatitis in adults with an often-associated history of photoallergy from ketoprofen. Patients with photoallergy from ketoprofen frequently have positive photopatch test reactions to octocrylene. These patients need to be informed of sunscreen products not containing octocrylene, benzophenone-3, or fragrances.