Topical application of St. John’s wort (Hypericum perforatum L.) and of its metabolite hyperforin inhibits the allostimulatory capacity of epidermal cells - Schempp,C.M.; Winghofer,B.; Lüdtke,R.; Simon-Haarhaus,B.; Schöpf,E.; Simon,J.C. (Br J Dermatol, 2000)