Contact Allergy in Western Sweden to Propolis of Four Different Origins.

Propolis, which is produced by honeybees and is used in "natural" products, can cause contact allergy. The composition of propolis varies between regions, but little is known about how this variation affects contact allergenicity. The aims of this study were to investigate the frequency of propolis contact allergy in western Sweden, and whether the frequency varies according to the origin of the propolis.