Urinary tract infections (UTIs) can occur when bacteria find their way into the bladder or the kidneys. These bacteria are normally found on the skin around the anus or sometimes around the vagina.

Normally, there are no bacteria in the urinary tract itself. However, certain things can make it easier for bacteria to enter or stay in the urinary tract. These include:

* A problem in the urinary tract, called vesicoureteral reflux, which is usually present at birth. This condition allows urine to flow back up into the ureters and kidneys
* Brain or nervous system illnesses (such as myelomeningocele, spinal cord injury, hydrocephalus) that make it harder to completely empty the bladder
* Bubble baths or tight-fitting clothes (girls)
* Changes or birth defects in the structure of the urinary tract
* Not urinating (peeing) often enough during the day
* Wiping from back (near the anus) to front after going to the bathroom. In girls, this can bring bacteria to the opening where the urine comes out

UTIs are more common in girls, especially around age 3 when they first begin toilet training. In boys who are not circumcised, the risk for UTIs is slightly higher before the first birthday.