Urinary tract infections are common in women. About 10 to 20 percent of all women get a lower urinary tract infection at least once. Infection is most likely in sexually active women ages 20 to 40. It occurs often when a woman becomes sexually active for the first time or after a long spell of not being sexually active.
Most bladder infections enter from the urethra.
The urethra is the body's tube that connects the bladder to the outside of the body. In women, the urethra is a short tube. All women have bacteria residing near the opening of the urethra, which is located near the top of the opening to the vagina. The bacteria are normally kept under control by our immune defenses. Passing urine acts to flush germs out.