Many causes of bedwetting have been proposed by researchers over the years, with no one single cause supported by research. Instead, bedwetting (primary nocturnal enuresis) is multifactorial — usually resulting from a number of factors at play that results in a child wetting. Understanding what medical factors are at work will help you decide an appropriate approach to treatment and credible resources to assist you.
Sleep or Arousal Disorder
Many children with bedwetting are described as deep sleepers, or children who are not easily roused from sleep, by their parents. Sleep studies to document a specific disturbance in sleep patterns or sleep arousal have been controversial. Wetting appears to occur at all stages of the sleep cycle. Although the specific mechanism requires additional research, it is generally accepted that children are not easily roused from sleep and are often disoriented when awakened.
A small percentage of children are sensitive to foods that contribute to nocturnal enuresis. A number of children benefit from eliminating foods such as citrus, caffeine and others.
High Urine Production
In most people the release of a hormone at night called vasopressin reduces the amount of urine produced. Some children with nocturnal enuresis release less vasopressin at night (i.e. no decrease in urine volume). These children produce more urine than their peers and are more prone to bedwetting - especially when other factors are present.
Low Functional Bladder Capacity
Another common factor in children with bedwetting is a small functional bladder capacity. These children have less forewarning of the need to urinate and feel more urgency. Some of these children may also exhibit daytime symptoms. When a child's functional bladder capacity is low they are less able to hold a normal amount of urine at night.
Irregular Bowel Movements
Some children with bedwetting are affected with bowel problems such as irregular or infrequent bowel movements or constipation. When the rectum is full, the bladder's expansion may be restricted or result in decreased sensitivity to bladder fullness.
Other causes of bedwetting, although uncommon, include anatomic abnormalities, endocrine disorders and urinary tract infections.