Continuous surveillance of contact allergy based on network data offers the identification of time trends or persisting problems, and thus enables focussing in-depth research (subgroup analyses, exposure analysis) on areas where it is needed.

Background Clinical surveillance of the prevalence of contact allergy in consecutively patch tested patients is a proven instrument to continually assess the importance of contact allergens (haptens) assembled in a baseline series. Objectives To present current results from the European Surveillance System on Contact Allergies, including 13 countries represented by 1 to 11 departments. Methods Anonymized or pseudonymized patch test and clinical data from various data capture systems used locally or nationally as transferred to the Erlangen data centre were pooled and descriptively analysed after quality control. Results In the 4 years (2015‐2018), data from 51 914 patients patch tested with the European baseline series (EBS) of contact allergens were analysed. Contact allergy to nickel was most frequent (17.6% positive), followed by contact allergy to fragrance mix I (6.9%), methylisothiazolinone (MI; 6.2%), and Myroxylon pereirae resin (balsam of Peru; 5.8%). Conclusions While the prevalence of MI contact allergy decreased substantially following regulatory intervention, the persistently high levels of allergy to metals, fragrances, other preservatives, and rubber chemicals point to problems needing further research and, potentially, preventive efforts. Results with national additions to the baseline series provide important information on substances possibly to be considered for inclusion in the EBS.

Data from one department per country give valuable insights into the spectrum of contact allergy prevalence rates in that country, but are not as representative as national data pooled from several departments.

Members of the ESSCA and EBS Working Groups, and GEIDAC are provided in Appendix section.

OSD definitions vary between European countries and are not directly comparable, which hampers comparisons between statistics collected in different countries. Awareness of this fact and further efforts for standardization are necessary.