The frequency of specific contact allergies is reduced in patients with psoriasis

Background Earlier studies suggested an inverse association between contact allergy and psoriasis, although the results of clinical studies have been inconsistent. Gene expression studies in human contact allergy focusing on immune responses revealed nickel being an inducer of T helper (Th)1/Th17 and some Th22 immune polarization, whereas fragrances were found to promote a Th2-dominated immune activation. Objectives To investigate the epidemiological association between contact allergy and psoriasis in a large multicentre cohort and to analyse the sensitization profile to specific allergens in these patients. Methods Retrospective analysis of patch-tested patients from 56 departments of dermatology (1996-2015), including 2387 patients with psoriasis and 161 989 control patients. All patients with atopic dermatitis were excluded from both groups. Results The odds ratio (OR) for contact allergy was calculated to be 0 center dot 55 in patients with psoriasis (95% confidence interval 0 center dot 50-0 center dot 59). Logistic regression analyses with several independent variables indicated a 'protective effect' of having psoriasis for most allergens, independently of age, sex, affected body site and patch test indication. Fragrance mix II (OR 0 center dot 36) and lanolin alcohols (OR 0 center dot 38) were found to be among the least common allergens in patients with psoriasis. In contrast, the frequency of contact dermatitis to nickel was only marginally affected in patients with psoriasis compared with controls (OR 0 center dot 75). Conclusions The inverse association between psoriasis and allergic contact sensitization is likely to be not exclusively mediated by psoriasis itself. The polarization of the activated immune response by specific allergens may influence the occurrence and significance of contact allergies in underlying immune-mediated diseases, eventually even beyond the skin.