Contact urticaria: Frequency, elicitors and cofactors in three cohorts (Information Network of Departments of Dermatology; Network of Anaphylaxis; and Department of Dermatology, University Hospital Erlangen, Germany)

BACKGROUND Contact urticaria (CU) is an infrequent, mostly occupational disease that may be life-threatening (CU syndrome stage 4). OBJECTIVES To identify the current frequency, elicitors and cofactors of CU. PATIENTS Three cohorts were retrospectively analysed for CU: (a) patients from the Information Network of Departments of Dermatology (IVDK) database (2000-2014; n = 159 947); (b) patients from an allergy unit (Department of Dermatology, University Hospital Erlangen, 2000-2015; n = 4741); and (c) patients from the Anaphylaxis Registry (2007-2015: 6365 reported cases, including 2473 patients with Ring and Messmer grade III-IV reactions) for severe cases with skin/mucosal manifestations occurring at the workplace vs cases not occurring at the workplace (n = 68 vs n = 1821). RESULTS Four hundred and forty-eight CU patients (0.28%) were diagnosed in the IVDK cohort, and 16 (0.34%) (10 of immunological aetiology, and 6 of non-immunological aetiology) in the Erlangen cohort. The most frequent elicitors in the IVDK cohort were cosmetics, creams, sun protection agents (although these were less frequent in CU patients than in controls without CU; 26.8% vs 35.6%, P