Interstitial cystitis is a long-term (chronic) problem in which pain, pressure, or burning is present in the bladder. It is also called painful bladder syndrome. The bladder is a hollow organ with a thin layer of muscle that stores urine. When your bladder fills up with urine, it sends a signal to your brain, telling the muscles to squeeze. In most people, these signals are not sent until your bladder is almost full. If you have interstitial cystitis, the signal to empty your bladder is sent more often or when your bladder is not very full. The condition most often occurs between ages 30 to 40, although it has been reported in younger people.