Eosinophilic cystitis (EC) is a rare inflammatory bladder condition caused by the build up of eosinophils in the bladder. The exact cause of this condition is not known. However, EC has been found in those with allergies and asthma, and in those with a history of bladder trauma or infection, open bladder surgery, or surgery for a bladder tumor. EC has also been found in those who take certain medications.