An involuntary leakage of urine that occurs when sneezing, coughing, lifting heavy objects or during physical exertion, but is not accompanied by the urge to urinate, indicates a weakness in the bladder closure mechanism. Under exertion such as coughing, the bladder pressure exceeds the closure pressure of the urethral sphincter, resulting in an involuntary leakage of urine. Known as stress incontinence, this form of involuntary leakage is attributable to a weak urethral sphincter. The risk of stress incontinence increases with age and is far greater among women than men. In women, a weakness of the bladder sphincter and stress incontinence can have two possible causes: a lowering of the bladder and uterus, or a paralysis of the urethral sphincter. In men, a prostate operation is the most frequent cause of stress incontinence.