Bed wetting types and causes

Bed wetting is a common problem which can be distressing for both children who wet the bed and their parents. Understanding the causes of bed wetting, and particularly that wetting the bed is not caused by naughtiness or other behavioural problems, is an essential part of dealing with a child’s bed wetting problem. Knowing that bed wetting is a process the child can’t always control, at what age it normally stops and when it may require treatment is important for determining when to seek professional help. When you speak to a healthcare professional about the problem they will ask some questions that will help to determine the cause of bed wetting and what treatment will be most effective.

So what is bed wetting, what causes it and when does it require treatment?

Bed wetting, or nocturnal enuresis to use the medical terminology, is the involuntary passage of urine at night. It’s a surprisingly common condition. Until age 3–4, most children wet the bed at least sometimes because they have not developed adult patterns of urinary control which allow them to ‘hang on’ until morning. By 5 years of age, about 4 out of every 5 children develop an adult pattern of urinary control which enables them to stay dry throughout the night.

However, 1 in 5 children experience bed wetting beyond age 5, and 1 in 10 continue to wet the bed at 10 years of age. Bed wetting after age 5 is more common in boys than in girls, with one study showing that 15 to 22% of 7 year old boys are bed wetters, compared to only 7 to 15% of 7 year old girls.

Given the psychological impact this condition can have, it’s surprising that only 34% of Australian families with a child who wets the bed seek professional help. And when parents fail to talk to a healthcare professional to get treatment advice, the majority of techniques they try themselves may not work.

It is important to remember that bed wetting is not an act of rebellion; it’s a process your child cannot control. It is essential never to blame or shame a child for wetting the bed. This will not help solve the problem, but may increase the distress your child experiences as a result of bed wetting.

Most children who wet the bed are distressed about it and this can cause social problems like low self-esteem, underachieving at school and difficulty in relationships with peers and parents. Behavioural problems like attention deficit hyperactivity disorder which often go hand-in-hand with bed wetting were once thought to cause bed wetting. However, they are now recognised to occur as a result of bed wetting.

But if bed wetting isn’t an act of rebellion or a psychological condition, what causes the problem?

Types of bed wetting

To get to grips with what are believed to be the main causes of bed wetting, it helps to understand that there are two ‘types’ of bed wetting: Primary and secondary nocturnal enuresis (bedwetting).

Primary bed wetting is more common. It is where a child has never been dry at night for a period of more than 6 months. Secondary bed wetting is when night time wetting begins after a period of at least 6 months of dry nights.

Each of these types has different causes and needs to be dealt with in different ways. Your healthcare professional will know all about this.

First, let’s take a look at primary nocturnal enuresis (bed wetting).

Primary bed wetting

If your child has primary nocturnal enuresis (bedwetting), your healthcare professional will enquire if the child only wets at night without any daytime symptoms (known as monosymptomatic nocturnal enuresis) or if the child wets at night and has daytime symptoms, such as frequency and urgency of urination which may occur with or without incontinence (known as non-monosymptomatic nocturnal enuresis). If non-monosymptomatic nocturnal enuresis is present, the daytime symptoms need to be treated first. Usually the individual will be referred to a specialist for further evaluation.

There are three main causes of primary bed wetting: difficulty rousing from sleep, an overactive bladder and overproduction of urine at night.

Difficulty rousing from sleep
Sleep arousal defects may cause primary bed wetting. Some children have a higher arousal threshold than others, which means that they find it more difficult to wake up. Why some children find it more difficult to wake up than others and the reasons they do not wake up in response to a full or contracting bladder are not yet fully understood. However, reduced arousal threshold is a recognised cause of bed wetting.

Overactive or “twitchy” bladder
Another common cause of primary nocturnal enuresis is reduced bladder capacity resulting from an overactive bladder. In this condition the bladder muscles become “twitchy” and, as a result, the bladder can only hold a small amount of urine. Reduced bladder capacity is thought to cause the condition in about one-third of children with primary bed wetting. At night when they are asleep the bladder may spontaneously contract which can result in wetting.

Overproduction of urine at night
A condition called nocturnal polyuria, which causes urine production to increase overnight, appears to cause bed wetting in as many as two-thirds of children with primary nocturnal enuresis. In this condition, increased urine production occurs as a result of abnormalities in the production of the substance vasopressin. The brain normally produces vasopressin during the night to reduce the amount of urine produced and allow an uninterrupted night’s sleep. When insufficient amounts of vasopressin are produced, urine production increases and the bladder fills more than it normally would. It’s a situation that makes it practically impossible for the bladder to “hold on” to urine until the next morning.

The initial treatment for an individual with primary bed wetting without daytime symptoms (monosymptomatic nocturnal enuresis) is an enuresis alarm, which triggers when wetting begins. The alarm noise wakes the child and alerts them that wetting has occurred. The child must then rise to finish urinating in the toilet. If, for whatever reason, alarm therapy doesn’t work or can’t be used, medications are usually the next step to treat bed wetting. Desmopressin is a medication that works like vasopressin, a substance produced in the brain which controls urine production during the night.

For more information about how and why our body produces urine, see Urinary Tract.

Risk factors (conditions associated with bed wetting but which do not cause a child to wet the bed) for primary nocturnal enuresis include:

Upper-airway obstruction and/or sleep apnoea, conditions which may cause difficulty breathing during sleep. These conditions are in turn often associated with impaired arousal from sleep which may underlie bed wetting;
Constipation, which is often associated with reduced bladder capacity;
Attention deficit hyperactivity disorder, which, like other behavioural disorders, is considered a result and not a cause of bed wetting;
Genetics; that is, whether or not the child’s parents experienced bed wetting. If both parents were bed wetters as children, their child has a 70% chance of inheriting the problem. The risk drops to around 40% if only one parent wet the bed as a child.

Secondary bed wetting

In secondary bed wetting, night time wetting begins after a period of at least 6 months of dry nights. While some of the risk factors for the primary type of bed wetting also apply to secondary bed wetting (such as constipation and obstruction of the upper-airway), there are also other conditions associated with the secondary form. They include:

Understanding the types of bedwetting and the causes are important because it can help determine which type of treatment is most likely to produce a successful result. Most children will grow out of bed wetting without the help of a doctor, but not all do.

Experts therefore advise that affected children and their families should seek professional help early.

The good news is that bed wetting can be treated effectively. It’s important to remember that most children who wet the bed don’t do it to be naughty or to rebel. They often find bed wetting an embarrassing problem and want to stop. If your child is 6 years or older and is motivated to be dry, seeing a healthcare professional and discussing your child’s bed wetting pattern and treatment options is the best way to support them and help resolve their bed wetting issue.

For more information about diagnosis, treatment options, shared bed wetting experiences and more, see Bed Wetting.

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