Why does bedwetting happen? 

JCP 1325

Knowing a little about the function of the kidneys and bladder will help to explain why bedwetting happens, so here’s a quick lesson in human biology:

How the body makes urine

The kidneys are responsible for filtering all the blood circulating in our bodies.  During this process some fluid and nutrients are re-absorbed back into the blood, while excess water and waste products are concentrated to form urine.

The urine then passes down tubes called ureters to the bladder, which is a muscular, stretchy balloon-like bag. The bladder has two functions: firstly to store urine and secondly to expel it via another tube called the urethra.

Night time and bedwetting

While we’re asleep, the pituitary gland releases higher levels of an antidiuretic hormone (ADH) which tells the kidneys to slow down the production of urine. Some children don't yet make enough of this hormone, which means their kidneys continue to produce urine at the same rate as during the day – one of the reasons why they wet the bed.

It could also happen because their brain simply isn't responding to signals from the bladder. Either way, the child doesn't recognise that the bladder is full, stays asleep and involuntarily releases urine from the bladder.

What's important to remember is that bedwetting isn’t something children have any control over. It is likely to resolve quite naturally, but some children may need a bit of extra help from a local health professional.