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Harvard Medical School

Bed-Wetting (Enuresis)

What Is It?

Bedwetting, also called nocturnal enuresis, means that a child accidentally passes urine at night during sleep. Because this is normal in infants and very young children, bedwetting is not considered a medical problem unless it happens in a child who is already in elementary school or who was completely dry day and night and then began to wet the bed again during the night. By age 5, 80% to 85% of children are consistently dry throughout the night. After age 5, the number of children who continue to wet the bed decreases by about 15% per year, even without treatment. Only 1% of children still wet the bed by the time they are 15 years old.

To help make diagnosis and treatment easier, doctors sometimes classify bedwetting into two types, primary and secondary nocturnal enuresis. In primary nocturnal enuresis, the child has never been consistently dry at night. In secondary nocturnal enuresis, the child has been dry at night for at least three to six months (or one year, according to some experts) and has begun to wet the bed again. It is very important to remember that in both types, the child is not wetting the bed on purpose.

Primary Nocturnal EnuresisThis is the most common type of nocturnal enuresis, affecting 90% of the estimated 6 million American children who wet the bed. Pediatricians think is caused by several developmental, genetic and hormonal factors acting together.

• Developmental factors — Children with prolonged bedwetting may not yet be able to recognize that the bladder is full, or may not have developed enough control over the bladder's urinary sphincter (the muscle that controls the bladder opening) to stop urinating during sleep. In some children, areas of the brain that control arousal also may be affected, allowing the child to sleep through a full bladder rather than waking up to urinate.

• Genetic (hereditary) factors — If both parents wet the bed when they were younger, three out of four of their children will have bedwetting problems. If only one parent wet the bed as a child, the odds decrease to slightly less than half. If neither parent wet the bed as a child, the odds that a child will wet the bed drops to one out of seven.

• Recently, researchers have pinpointed chromosome 13 as the home of the bedwetting gene. Further research continues in this area.

• Hormonal factors — Under normal circumstances, the body's level of a hormone that decreases the production of urine by the kidneys (antidiuretic hormone, or ADH) rises during sleep, causing the bladder to fill more slowly. In some children who wet the bed, this nighttime rise in antidiuretic hormone does not happen as expected. Therefore, the amount of urine made remains the same as during waking hours, so the bladder continues to fill as much as it would during the daytime.

• Other factors — Some children with prolonged nighttime bedwetting may simply have smaller bladders compared with their "dry" peers.

Although the specific combination of factors varies from child to child, the result is the same — bedwetting. In a small number of cases, primary nocturnal enuresis arises from a purely medical problem, such as a physical defect in the child's urinary tract, a neurological problem related to the spinal nerves or brain, or a urinary tract infection.

Secondary Nocturnal EnuresisWhen a child starts to wet the bed again after being dry for months or sometimes even years, there is often an identifiable cause. One of the most common is stress, when a sudden change rocks a child's world. Almost any change in the environment — good or bad — can be a trigger; for example, a new baby, a death in the family, parents' divorce or marriage problems, a new home or school, or even a long visit from relatives. Secondary bedwetting may be related to sexual abuse or to extreme bullying. Rarely, this form of bedwetting is related to a medical problem, such as a urinary tract infection or diabetes, and in these cases there are usually other obvious symptoms of medical illness.