To control urination, two muscles must be used: the sphincter and the detrusor. The sphincter is a muscle that wraps around the urethra tube, which carries urine out of the body. Squeezing the sphincter stops the flow of urine. The detrusor is the bladder wall muscle, which must be relaxed for the bladder to fill with urine and contracted for it to empty.

If the pressure between these two muscles is even, a person will remain continent. When the pressure on the urethra decreases while it increases on the bladder, a person has the urge to urinate and will void normally. However, someone suffering from SUI does not have control of the sphincter and the pressures are not balanced, causing leakage.

SUI is rare in men, although it can occur after a prostatectomy (removal of the prostate). Women are the primary sufferers, because pregnancy and childbirth weaken the pelvic muscles.

Because SUI is an embarrassing condition, and one patients may not even want to discuss with their doctors, it is under-reported and under-diagnosed. In one 2004 National Institutes of Health study, the rate of SUI in women in the United States varied between 4 percent and 35 percent. The Food and Drug Administration (FDA) says it’s between 20 and 40 percent.

Conservative treatments for SUI include Kegel exercises, losing weight, reducing caffeine intake and avoiding strenuous activities. For mild cases, women can wear absorbent pads. In severe cases, surgery may be necessary to correct incontinence. Bladder slings — narrow strips of tissue or surgical mesh — can be implanted below the bladder to restore continence. However, when these slings are implanted transvaginally, or through the vagina, there can be serious complications.

By its nature, SUI is likely to affect the quality of life for a woman because it interferes with romantic relationships, social activities and even careers. When a woman cannot be confident she will not leak urine in public, it certainly curtails her desire to engage in personal and professional activities.