For up to a million women in the U.S., enjoying a piece of pepperoni pizza has painful consequences. They have a chronic bladder condition called interstitial cystitis that causes severe pelvic pain. Spicy food such as citrus, caffeine, tea (even green tea), sodas, tomatoes and alcohol can cause their symptoms (pain and an urgent need to frequently urinate) to flare up and intensify the pain. It was thought that the spike in their symptoms was triggered when digesting the foods produced chemicals in the urine that irritated the bladder.

However, researchers from Northwestern University's Feinberg School of Medicine believe the colon, irritated by the spicy food, is to blame.