Dr. Mills breaks down the surprisingly complex process behind a seemingly simple bodily function, from the signals in your brain to the muscles of the bladder and prostate. He explains what urgency, nighttime bathroom trips, a weak stream and incomplete emptying may reveal about your health—and when they warrant a visit to the doctor. He also explores how caffeine, alcohol, medications, diabetes and heart problems can affect urinary habits, along with the risks of routinely holding it in. Plus, why does the urge suddenly strike when you reach your front door?