When the problem persists, however, a visit to the doctor is in order. The precise cause of bed-wetting is unknown. Most cases appear to be due to delayed physical development. Bladder capacity may be less than half what is considered normal for the child's age. Some researchers, in fact, have argued that boys aren't normally dry at night until age 8.
Several studies point to a genetic link in enuresis.
But the figure dropped to 44 percent when only one parent had wet the bed in childhood. By contrast, when neither parent had enuresis, only 15 percent of the children did. A frequent cause of bed-wetting is constipation. In fact, treatment of constipation in enuretic children often resolves the wetting, report Sean O'Regan, M.D., and others of the Pediatric Research Center, University of Montreal. In the March 1986 American Journal of Diseases of Children, they explained that, in chronically constipated children, the rectum is probably never empty so the rectal sphincter muscle remains contracted to hold back stool.