Bed-wetting: What Causes It?

Waking in the middle of the night to change your child's sheets after a bed-wetting episode is practically a rite of passage for parents. And it's more common than you think.

"I call it the hidden problem of childhood," says Howard Bennett, MD, a pediatrician and author of Waking Up Dry: A Guide to Help Children Overcome Bedwetting. "Unlike asthma or allergies, it's just not talked about outside the house."

Bed-wetting: The Secret Problem

That secrecy about bed-wetting makes the situation tougher for kids and parents alike. "Ninety percent of kids think they're the only ones who wet the bed, which makes them feel even worse," says Bennett.

Yet bed-wetting children are far from alone. Though children naturally gain bladder control at night, they do so at different ages. From 5 to 7 million kids wet the bed some or most nights -- with twice as many boys wetting their bed as girls. After age 5, about 15% of children continue to wet the bed, and by age 10, 95% of children are dry at night.

Wet beds leave bad feelings all around. Frustrated parents sometimes conclude a child is wetting the bed out of laziness. Kids worry there's something wrong with them -- especially when teasing siblings chime in. Fear of wetting the bed at a friend's sleepover can create social awkwardness.

For some, bed-wetting may be an inevitable part of growing up, but it doesn't have to be traumatic. Understanding bed-wetting's causes is the first step to dealing with this common childhood problem.

The Bed-wetting Gene

There's no one single cause of bed-wetting, but if you want an easy target, look no further than your own DNA.

"The majority of bed-wetting is inherited," says Bennett. "For three out of four kids, either a parent or a first-degree relative also wet the bed in childhood."

Scientists have even located some of the specific genes that lead to delayed nighttime bladder control. (For the record, they're on chromosome 13, 12, and 8.)

"Most parents who had the same problem communicate it to their kids, which is good," suggests Bennett. "It helps a kid understand, I'm not alone, it's not my fault."

The Usual Bed-wetting Suspects

Yet genetics only tells part of the story. Researchers have identified a number of factors that likely contribute to bed-wetting. "All of these are debated, but each probably plays a role in some children," says Bennett, including:

• Delayed bladder maturation. "Simply put, the brain and bladder gradually learn to communicate with each other during sleep, and this takes longer to happen in some kids," Bennett tells WebMD.
• Low anti-diuretic hormone (ADH). This hormone tells the kidneys to make less urine. Studies show that some kids who wet the bed release less of this hormone while asleep. More urine can mean more bed-wetting.
• Deep sleepers. "Families have been telling us for years that their children who wet the bed sleep more deeply than their kids that don't," says Bennett. Research confirms the link. "Some of these children sleep so deeply, their brain doesn't get the signal that their bladder is full."
• Smaller "functional" bladder. Although a child's true bladder size may be normal, "during sleep, it sends the signal earlier that it's full," says Bennett. 
• Constipation. Full bowels press on the bladder, and can cause uncontrolled bladder contractions, during waking or sleep. "This is the one that's hiding in the background," says Bennett. "Once kids are toilet trained, parents often don't know how often a child is going ... [they're] out of the 'poop loop.'"