Effect of topical application of Hypericum perforatum extract (St. John's wort) on skin sensitivity to solar simulated radiation

St. John's wort (Hypericium perforatum) is a traditional folk remedy that i s used for the topical treatment of superficial wounds, scars and burns. A characteristic metabolite of St. John's wort is the photodynamic active pla nt pigment hypericin, It is known that hypericin may cause a severe photode rmatitis called hypericism when higher amounts of St. John's wort are inges ted orally. To date, no reports on the photosensitizing capacity of topical application of St. John's wort are available. Here, we investigated the ef fects of Hypericum oil (hypericin 110 mu g/mL) and Hypericum ointment (hype ricin 30 mu g/mL) on skin sensitivity to solar simulated radiation. Sixteen volunteers of the skin types II and III were tested on their volar forearm s with solar simulated radiation for photosensitizing effects of Hypericum oil (n=8) and Hypericum ointment (n=8), The minimal erythema dose (MED) was determined by visual assessment, and skin erythema was evaluated photometr ically, With the visual erythema score, no change of the MED could be detec ted after application of either Hypericum oil or Hypericum ointment (P>0.05 ). With the more sensitive photometric measurement, an increase of the eryt hema-index after treatment with the Hypericum oil could be detected (less t han or equal to 0.01). The results do not provide evidence for a severe pho totoxic potential of Hypericum oil and Hypericum ointment, detectable by th e clinically relevant visual erythema score. However, the trend towards inc reased photosensitivity detected with the more sensitive photometric measur ement could become relevant in fair-skinned individuals, in diseased skin o r after extended solar irradiation.