The causes of children’s bladder weakness

Bed wetting is the most common form of children’s incontinence, with day wetting affecting just 2-4% of 5 to 7 year olds. The following are the most common causes of children's bladder weakness.

Contributory Factors to bedwetting

To stay dry at night depends on 3 main factors involving the following: the amount of urine produced during the night, the ability of the bladder to hold on to that urine and being able to wake up to go to the toilet in response to signals from the bladder. A problem with any of these factors could result in the child wetting the bed. Another important factor that is often overlooked is the presence of constipation

Volume of night time urine

When we go to sleep the brain releases a chemical messenger called vasopressin that reduces the amount of urine the kidneys make. Making less urine at night allows an individual to sleep till morning without having to wake up to go to the toilet. Studies have shown that some children wet the bed because they do not make enough vasopressin and as a result make more urine than their bladder can hold on to.

Reduced Bladder Capacity and Overactive Bladder

Staying dry at night depends on the fine balance between the volume of urine produced and the ability of the bladder to hold on to that urine. If a child has a small bladder capacity for their age or an over active bladder, then this can affect their ability to store urine overnight. Some children have an apparently normally functioning bladder during the day which only becomes unstable overnight.

Reduced Bladder Capacity

Health professionals calculate that the average bladder capacity for a child is:
Their age x 30 + 30 = average capacity for age
 E.g. 7 x 30 + 30 = 240 mls average capacity for a 7 year old
So if your child is urinating much smaller amounts than this, then this could be a contributory factor. However it is always best to consult a health professional and let them do a full assessment of all possible contributory factors.

Overactive Bladder

Some children, mostly girls, have what is called an ‘overactive’ bladder. This means that the bladder does not stay relaxed as it is filling and will suddenly start to empty before it is full. Often it means the child gets the urge to empty their bladder more frequently than normal and has difficulties ‘holding on’. A urine infection or constipation can sometimes cause this problem.

Failure to wake

Children with nocturnal enuresis are unable to wake up from sleep in  response to full bladder signals. For many years, it was thought that children wet the bed in deep states of sleep. However, recent research demonstrated that some children, regardless of their sleep state, just don’t respond to their internal bodily signals to wake up, and so wet the bed.


Constipation is often an under recognised cause of bedwetting. If a child has a full rectum, it pushes against the bladder and can potentially reduce how much urine the bladder can hold and it can also induce involuntary contractions. Treatment of constipation alone can significantly improve if not cure the bedwetting.

The hereditary link

There appears to be a hereditary link to bedwetting, which can continue through several generations. Broadly speaking there’s a 40% likelihood of a child wetting the bed if one parent did, rising to 70% where it was both parents.

Day time problems

Some children have both day and night time wetting problems, whilst others just have a daytime issue. Children with day time problems can have what is called a ‘voiding’ or emptying problem when they are not able to empty their bladder properly with some urine (called residual urine) left behind. Other children can have what is a ‘storage’ problem when their bladders are not able to hold on to their urine to enable them to stay dry.

Children normally empty their bladders around 5-7 times per day. If children pass urine less frequently they are sometimes said to have ‘decreased urinary frequency’. This may be because they are not drinking enough during the day or delaying going to the toilet.

If your child passes urine more than 8 times per day they are said to have ‘frequency’ and this is sometimes associated with ‘urgency’, which is when the child suddenly has the feeling they need to pass urine with little or no warning, and has to dash to the toilet! Of course if they don’t make the toilet in time, they will have a wetting episode.

Unlike night time wetting, children with day time wetting may have an associated problem, such as a bladder that is overactive or does not empty properly, and this can get worse if left untreated. As a result, if you think your child may have a day time problem, you should consult a doctor or paediatric continence advisor.

Functional Incontinence

This is where your child is physically unable to reach the toilet. It may be due to problems with movement or it could be because your child uses a wheelchair. In the latter case, it may be that your child has both faecal and urinary incontinence. If your child is able to get to the toilet on their own but this takes time, make sure access to the toilet free is of obstacles and ensure they have clothing that is simple to remove.

Placing a potty or commode may help them empty their bladder more easily at night. For children who cannot get out of bed then the use of a hand held urinal may help – (urinals are available for both boys and girls either through your local healthcare service, by mail order or from your local pharmacy).

However the most important thing is to use protective underwear and bedding that keeps them dry and comfortable. This limits the risk of irritations and skin infections which are often suffered by people who are seated or lying down for long periods.

Medical Causes

Bladder weakness in children could also be a side effect of a medical condition or disability. In cases of cerebral palsy, spina bifida, brain injury or nerve damage, the ability to receive the correct signals from the brain to empty the bladder may be physically impaired. Occasionally a repeated urinary infection or even a minor deformity in the urinary tract could also be the cause.

If you’re a carer for a child with a serious injury or disability, you’ll find more information when you go to our Looking After Loved Ones section.


Anxiety may occur as a result from the wetting (being anxious about being able to get to the toilet on time or having a wetting accident in public is not uncommon) but is not regarded as a cause.

Toilet avoidance

Some children put off going to the toilet, either because they don’t like using the school facilities or because they don’t want to miss out on something and ignore their urge. This can lead to an overfilling of the bladder and accidental urination. It can also cause infections so try and encourage your child to ‘listen’ to their bladder and tackle any concerns they have about using the toilet away from home.

You will realise by now that there can be several causes of bladder weakness in children. Certainly, everyone’s experience is different. So if you’re unsure, we advise you to contact a healthcare professional for a personal assessment, which normally starts with finding out when your child experiences urine loss and under what conditions. It might be an idea to keep a diary recording your child’s urination pattern for a week so you can monitor what happens. You’ll then have a record to discuss with your Doctor or continence advisor should you wish to.