What causes VUR?

There are three main causes of VUR:

1. Some children are born with a faulty valve at the point where the ureter connects into the bladder. In a normal urinary tract, the ureter joins the outside of the bladder at an angle and then forms a long tunnel through the muscular tissue of the bladder. If this tunnel is long enough, it serves as an effective one-way valve. In children with VUR, this tunnel can be too short to work properly as a valve and thus urine may flow in both directions.
2. In some children, the ureters enter near the bottom of the bladder. A ureter that enters the bladder too far down does not make an effective valve and this can cause VUR. A child with this type of ureter is less likely to outgrow VUR on their own. 
3. A third cause of VUR is some type of blockage in the urethra which prevents urine from leaving the bladder. This results in greater pressure on the ureter valve, which may force the urine back through the valve and into the ureter.