A hormone is normally produced during sleep which reduces the volume of urine. This is called anti-diuretic hormone (ADH).

In addition to the arousal disorder which affects the brain's response to bladder signals, about 60% of children with nocturnal enuresis or bedwetting do not make this hormone. Therefore they produce a large volume of urine during sleep, which exceeds their bladder capacity.

However, once the bedwetter has trained their brain with a bedwetting alarm to wake to bladder signals during sleep, they can stay dry - they just need to go to the toilet more often than someone who produces ADH.

Once night control is established, ADH production is often activated.