Stress incontinence is the most common type. It occurs when the pressure in the bladder becomes too great for the bladder outlet to withstand. This is usually caused by weak pelvic floor muscles. Urine tends to leak most when you cough, laugh, sneeze or when you exercise (such as when you jump or run). In these situations there is a sudden extra pressure (stress) inside the tummy (abdomen) and on the bladder. Small amounts of urine often leak. Sometimes much larger volumes of urine are accidentally passed. Pelvic floor muscles are often weakened by childbirth. Stress incontinence is common in women who have had several children, in obese people and with increasing age. Stress incontinence can occur in men who have had some treatments for prostate cancer. This includes surgical removal of the prostate (prostatectomy), and radiotherapy.

Urge incontinence (unstable or overactive bladder) is the second most common cause. You have 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. In most cases, the cause of urge incontinence is not known. This is called idiopathic urge incontinence. It seems that the bladder muscle gives wrong messages to the brain and the bladder may feel fuller than it actually is. Sometimes urge incontinence can occur because of problems with the nervous system (the brain, spinal cord and other nerves in the body). Illnesses or diseases affecting the nervous system are called neurological disorders. Some people with certain neurological disorders may experience urge incontinence. Examples are Parkinson's disease, multiple sclerosis (MS), spinal cord injury and after a stroke.