Results of patch testing propolis in the European baseline series: A 4-year retrospective study.

Background: Propolis was added to the European baseline series (EBS) in 2019.

Objectives: To investigate the frequency and relevance of positive patch tests to propolis in the EBS and to study co-reactivities.

Patients and methods: Retrospective study in patients patch tested between June 2019 and November 2023 in a university hospital in Amsterdam, The Netherlands.

Results: Of 3134 consecutive patients, 299 (9.5%) had a positive reaction to propolis 10% pet. Only nine reactions (3%) were judged to be clinically relevant. There were significant co-reactivities to Myroxylon pereirae resin (balsam of Peru), colophonium, fragrance mixes 1 and 2, and to limonene and linalool hydroperoxides. A steep increase in rates of positive reactions to propolis was observed from 2020 to 2023. This was highly likely the result of the replacement of Chinese propolis with Brazilian propolis by the manufacturer.

Conclusions: Positive patch tests for propolis are very frequent in Amsterdam, but only a few of these reactions are relevant. Most are probably (pseudo-)cross-reactions in patients with fragrance allergies. Propolis in the EBS has very limited value for dermatologists and patients in The Netherlands. Changes in patch test materials should be provided to all users to avoid misinterpretation of patch test results.