Allergic contact dermatitis to Ginkgo biloba L.: relationship with urushiol.

A Ginkgo biloba L. fruit extract was prepared and purified. Three groups of guinea pigs were sensitized to the crude extract, anacardic acids 1, and cardanols 2 respectively, using the FCAT method, and the fourth group to urushiol using the epicutaneous route. Each group was tested for reaction to the primary sensitizer and to the different main aromatic compounds isolated from Ginkgo fruits. Anacardic acids were found to be good sensitizers, while cardanols failed to induce allergic contact dermatitis (ACD). No cross-reactions were observed among the compounds tested. Ginkgolic acids 1 seem to be the main allergens of Ginkgo biloba L. and the hypothesis of a biotransformation of 1 into catechol 4 is not supported by experiment.