Stress incontinence is an involuntary loss of urine that occurs during physical activity, such as coughing, sneezing, laughing, or exercise.

The ability to hold urine and control urination depends on the normal function of the lower urinary tract, the kidneys, and the nervous system. You must also have the ability to recognize and respond to the urge to urinate.

The average adult bladder can hold over 2 cups (350ml - 550 ml) of urine. Two muscles are involved in the control of urine flow:

• The sphincter, which is a circular muscle surrounding the urethra. You must be able to squeeze this muscle to prevent urine from leaking out.
• The detrusor, which is the muscle of the bladder wall. This must stay relaxed so that the bladder can expand.

In stress incontinence, the sphincter muscle and the pelvic muscles, which support the bladder and urethra, are weakened. The sphincter is not able to prevent urine flow when there is increased pressure from the abdomen (such as when you cough, laugh, or lift something heavy).

Stress incontinence may occur as a result of weakened pelvic muscles that support the bladder and urethra or because of a malfunction of the urethral sphincter. The weakness may be caused by:

• Injury to the urethral area
• Some medications
• Surgery of the prostate or pelvic area

Stress urinary incontinence is the most common type of urinary incontinence in women.

Stress incontinence is often seen in women who have had multiple pregnancies and vaginal childbirths, and whose bladder, urethra, or rectal wall stick out into the vagina (pelvic prolapse).

Risk factors for stress incontinence include:

• Being female
• Childbirth
• Chronic coughing (such as chronic bronchitis and asthma)
• Getting older
• Obesity
• Smoking