Stress incontinence is the most common type. It occurs when the pressure in the bladder becomes too great for the bladder outlet to withstand. It usually occurs because the pelvic floor muscles which support the bladder outlet are weakened. Urine tends to leak most when you cough, laugh, or when you exercise (such as when you jump or run). In these situations there is a sudden extra pressure ('stress') inside the abdomen and on the bladder. Small amounts of urine may leak, but sometimes it may be quite a lot and cause embarrassment. The common reason for the pelvic floor muscles to become weakened is childbirth. Stress incontinence is common in women who have had several children. It is also more common with increasing age and with obesity.

Urge incontinence (unstable or overactive bladder) is the second commonest cause. This is when you get an urgent desire to pass urine. Sometimes urine leaks before you have time to get to the toilet. The bladder muscle contracts too early and the normal control is reduced. The cause is not known but it seems that the bladder muscle gives wrong messages to the brain, and the bladder may feel fuller than it actually is.

Mixed incontinence. Some people have a combination of stress and urge incontinence.

More than 9 in 10 cases of urinary incontinence are due to the above causes. Other causes are less common. They include:

Neuropathic incontinence. This is when the nerves that control the bladder and surrounding structures are affected in some way. For example, some people with multiple sclerosis, spinal cord damage, brain disorders, etc, develop this type of incontinence.
 

Overflow incontinence. This is when there is an obstruction to the outflow of urine. The obstruction prevents the normal emptying of the bladder. A pool of urine constantly remains in the bladder that cannot empty properly. However, pressure builds up behind the obstruction. The normal bladder emptying mechanism becomes faulty and urine may leak past the blockage from time to time. An enlarged prostate gland in men is the common cause of this. Treatment depends on the cause. For example, removal of the prostate (prostatectomy) if an enlarged prostate is the cause.
 

Bedwetting (enuresis) occurs in many children, but some adults are affected.