Both oils can hurt the skin but are usually used interchangeably. Phototoxic oils usually contain high amounts of terpenes (compounds that absorb UV light) like citronella and linalool. Photosensitizing oils usually contain menthol and thymol which are both capable of causing allergic reactions when the body or scalp is exposed to direct UV light. There could be exceptions to this like essential basil oil due to its high amount of linalyl acetate which is also phototoxic, but its overall photo-sensitization potential is minimal.