Lyme disease from ticks starts with a rash.  Phytophotodermatitis is caused by limes of the citrus version.

Limes contain psoralen, a chemical that absorbs long-wave ultraviolet light.  The light waves excite the electrons in the psoralen to three times their normal energy state.  When they release this energy it literally burns the skin and results in a red, itchy rash with blistering.

Other foods that contain psoralen include lemons, parsley, celery, carrots, figs, fennel and parsnip.  In fact, another term for phytophotodermatitis is “grocery clerk’s hands”.

This name alludes to the fact that it is skin contact from handling or preparing the food that leads to the localized rash; not ingesting the food.