ABSTRACTBackgroundIn Amsterdam, in 2024, patch testing with Brazilian propolis yielded high rates of positive reactions (> 20%), whereas reactivity to Chinese propolis was significantly lower (3.5%). Differences in the composition were suggested as a possible explanation.Objectives1. To study the composition of 3 propolis samples (2 Chinese and 1 Brazilian) used for preparing commercial test allergens; 2. To study the influence of different enrichment times on the qualitative and quantitative composition of Brazilian propolis.Materials and MethodsAnalyses were performed using gas chromatography–mass spectrometry/flame ionisation detection (GC–MS/FID) of the volatile components obtained by headspace SPME (solid phase microextraction).ResultsA strong difference between the composition of the Brazilian propolis sample and both samples of Chinese propolis was found. Major ingredients in Brazilian propolis were hydrocinnamic acid (16.9%), (E)‐nerolidol (7.41%), spathulenol (5.45%) and junenol (4.01%). Major ingredients in Chinese propolis were (E)‐cinnamyl alcohol (8.08% and 24.96%), 2‐phenethyl alcohol (8.93% and 11.25%), α‐curcumene (8.77% and 8.81%) and guaiol (5.96% and 5.72%).ConclusionsThe volatile fractions of Brazilian propolis and Chinese propolis used for patch testing have very different compositions. Whether this causes or contributes to the differences in patch test reactivity has to be investigated further.