Background: Propolis, the bee glue, is increasingly used in biocosmetics and for the self-treatment of various diseases.
Objective: Patients reacting to propolis were requested to participate in further testing with the breakdown constituents of the bee glue.
Methods: Twenty-seven patients agreed to be tested with 18 constituents, including four caffeates (the typical allergens of propolis) derived from the sticky exudates of poplar buds.
Results: Seven patients did not react to the propolis constituents tested. In the remaining 20 patients, the four caffeates produced strong reactions. Phenylethyl caffeate, which produced positive reactions in 20 patients, was the leading contact allergen. Benzyl caffeate elicited strong responses in 18 patients, and 3-methyl-2-butenyl caffeate produced reactions in 17 patients. Geranyl caffeate produced positive reactions in 11 patients. The flavonoid tectochrysin gave positive results in 2 patients; ferulic acid, coumaric acid, and methyl cinnamate produced weak responses.
Conclusions: In middle Europe, the caffeates are the responsible allergens in propolis allergy. Patients from other countries, where poplar trees do not grow, become allergic to other propolis constituents but not to the caffeates.