20 Years of standard patch testing in an eczema population with focus on patients with multiple contact allergies

Results of standard patch tests performed with the same methodology in one centre are rarely available over a large time span. This gives the unique opportunity to study not only prevalence but also persistency of contact allergy and characterize subpopulations. The objectives were to investigate sensitivity rates and persistencies of patch test results and characterize patients with multiple contact allergies. A 20-year retrospective database-based study of 14 998 patients patch tested with the European Standard Series was performed. 34.5% were sensitized, primarily women. Sensitivity to nickel was most frequent and least frequent to mercaptobenzothiazole, N-isopropyl-N-phenyl-p-phenylenediamine and benzocaine. Yearly proportion of negative, mono/double-allergic, and multiple-allergic cases remained stable. Persistency of positive reactions was high for para-phenylenediamine, Cl(Me)isothiazolinone, and primin and poor for paraben mix. 5.1% were multiple allergic, primarily women, and 90% got diagnosed by the first test. Frequency of multiple allergies increased with age. More multiple- than mono/double-allergic patients were tested multiple times. Persistency and sensitivity rates in a Danish eczema population are provided and are useful for decisions regarding the standard series. Patients with multiple contact allergies are typically elderly women who might have long-lasting and hard-to-treat eczema. Cumulative environmental exposure seems necessary to develop multiple allergies.