Urine leaves the body through the urethra, a tube connected to the bladder. During urination, bladder muscles contract, forcing urine into the urethra. Urine flows out of the body when the sphincter muscles surrounding the urethra relax. Incontinence occurs when the bladder muscles contract suddenly or when the urethra muscles relax suddenly. Physical changes such as pregnancy and childbirth can lead to stress incontinence.
Stress incontinence occurs due to the weakening of pelvic floor muscles that support the bladder.
When weakened, the bladder tends to move down preventing the muscles that shut the urethra from squeezing as tight as they should. The week before a woman s menstrual cycle can also lead to stress incontinence due to lowered estrogen levels which in turn lowers muscle pressure around the urethra causing leakage. This is caused by inappropriate bladder contractions. People who experience urge incontinence can lose urine during sleep, after drinking a small amount of water, when they touch water or when they hear water running. These involuntary actions of the bladder muscles occur due to damage to the nerves of the bladder, to the nervous system or to the bladder muscles themselves.