Causes

Normal bladder function

The kidneys produce urine, which drains into your bladder. When you urinate, urine passes from your bladder through a tube called the urethra (u-REE-thruh). A muscle in the urethra called the sphincter opens to release urine out of the body.

In women, the urethral opening is located just above the vaginal opening. In men, the urethral opening is at the tip of the penis.

As your bladder fills, nerve signals sent to your brain eventually trigger the need to urinate. When you urinate, these nerve signals coordinate the relaxation of the pelvic floor muscles and the muscles of the urethra (urinary sphincter muscles). The muscles of the bladder tighten (contract), pushing the urine out.

Involuntary bladder contractions

Overactive bladder occurs because the muscles of the bladder start to contract involuntarily even when the volume of urine in your bladder is low. These involuntary contractions create an urgent need to urinate.

Several conditions may contribute to signs and symptoms of overactive bladder, including:

• Neurological disorders, such as stroke and multiple sclerosis
• Diabetes
• Urinary tract infections that can cause symptoms similar to those of an overactive bladder
• Hormonal changes during menopause in women
• Abnormalities in the bladder, such as tumors or bladder stones
• Factors that obstruct bladder outflow — enlarged prostate, constipation or previous operations to treat other forms of incontinence

Other factors that may be associated with your symptoms include:

• Medications that cause a rapid increase in urine production or require that you take them with lots of fluids
• Excess consumption of caffeine or alcohol
• Declining cognitive function due to aging, which may make it more difficult for your bladder to understand the signals it receives from your brain
• Difficulty walking, which can lead to bladder urgency if you're unable to get to the bathroom quickly
• Incomplete bladder emptying, which may lead to symptoms of overactive bladder, as you have little urine storage space left

The specific cause of an overactive bladder may be unknown.