The cause of a bladder infection is usually bacteria settling in the bladder. The factors that lead to bacteria in the bladder may vary depending on age and gender. Bacteria may come from the skin around the genitals and rectum. The most common bacteria causing bladder infections is E.coli which occurs naturally in the colon, but Chlamydia and Mycoplasma may also be culprits. For children, an obstruction to the urinary flow from a physical abnormality or a dysfunctional emptying of the bladder may cause urine to back up into the body, increasing the risk of a bladder infection. For men, a bladder infection is often connected to problems with the prostate. For women, using a diaphragm, sexual intercourse, pregnancy, and menopause can all influence the possibility of bladder infection.