Ureters (tunnels) carry urine from the kidneys to the bladder through the bladder wall. At the end of the tunnel, a flap-like valve prevents urine from backing-up into the ureters and kidneys.

In some children, the valves may be abnormal or the ureters in the bladder may not travel deep enough into the bladder wall, which can cause vesicoureteral reflux. Vesicoureteral reflux is a condition that allows urine to flow back up into the ureters and kidneys, causing repeated urinary tract infections. The reflux of urine exposes the ureters and kidney to infection from bacteria and high-pressure generated by the bladder during urination.  If left untreated, urinary infections can cause kidney damage, renal scarring (potentially stunting kidney growth), and high blood pressure later in life.

Vesicoureteral reflux is treated with antibiotics, or, in severe cases, with surgery.