Earl Grey tea
In several patch test studies, application of some sources of bergamot oil directly to the skin of guinea pigs was shown to have a concentration-dependent phototoxic effect of increasing redness after exposure to ultraviolet light (due to the chemical bergapten, and possibly also citropten, bergamottin, geranial, and neral). This is a property shared by many other citrus fruits and other members of Rutaceae including Rue. Bergapten has also been implicated as a potassium channel blocker; in one case study, a patient who consumed four litres of Earl Grey tea per day (which contains bergamot essential oil as a flavouring) suffered muscle cramps.