Bedwetting

Two physical functions prevent bedwetting. The first is a hormone that reduces urine production at night. The second is the ability to wake up when the bladder is full. Children usually achieve nighttime dryness by developing one or both of these abilities. There appear to be some hereditary factors in how and when these develop.

The first ability is a hormone cycle that reduces the body's urine production. At about sunset each day, the body releases a minute burst of antidiuretic hormone (also known as arginine vasopressin or AVP). This hormone burst reduces the kidney's urine output well into the night so that the bladder does not get full until morning. This hormone cycle is not present at birth. Many children develop it between the ages of two and six years old, others between six and the end of puberty, and some not at all.

The second ability that helps people stay dry is waking when the bladder is full. This ability develops in the same age range as the vasopressin hormone, but is separate from that hormone cycle.

Most children develop the ability to stay dry as they grow older. The typical development process begins with one- and two-year-old children developing larger bladders and beginning to sense bladder fullness. Two- and three-year-old children begin to stay dry during the day. Four- and five-year-olds develop an adult pattern of urinary control and begin to stay dry at night.