In vitro photochemical and phototoxicological characterization of major constituents in St. John's Wort (Hypericum perforatum) extracts

► Photochemical properties of SJW extract and constituents were characterized. ► Some SJW constituents exhibited ROS generation under light exposure. ► Hypericin, pseudohypericin and hyperforin might be responsible for in vitro phototoxicity of SJW.