Urinary incontinence is when the normal process of storing and passing urine is disrupted. This can happen for several reasons. Certain factors may also increase your chance of developing urinary incontinence. Some of the possible causes lead to short-term urinary incontinence, while others may cause a long-term problem. If the cause can be treated, this may cure your incontinence.

Causes of stress incontinence

Stress incontinence is when the pressure inside your bladder as it fills with urine becomes greater than the strength of your urethra to stay closed. Your urethra is the tube that urine passes through to leave the body.

Any sudden extra pressure on your bladder, such as laughing or sneezing, can cause urine to leak out of your urethra if you have stress incontinence.

Your urethra may not be able to stay closed if the muscles in your pelvis (pelvic floor muscles) are weak or damaged, or if your urethral sphincter – the ring of muscle that keeps the urethra closed – is damaged.

Problems with these muscles may be caused by:

• damage during childbirth – particularly if your baby was born vaginally, rather than by caesarean section
• increased pressure on your tummy – for example, because you are pregnant or obese
• damage to the bladder or nearby area during surgery – such as the removal of the womb (hysterectomy), or removal of the prostate gland
• neurological conditions that affect the brain and spinal cord, such as Parkinson's disease or multiple sclerosis

Causes of urge incontinence

The urgent and frequent need to pass urine can be caused by a problem with the detrusor muscles in the walls of your bladder. The detrusor muscles relax to allow the bladder to fill with urine, then contract when you go to the toilet to let the urine out.

Sometimes the detrusor muscles contract too often, creating an urgent need to go to the toilet. This is known as having an overactive bladder. The reason your detrusor muscles contract too often may not be clear, but possible causes include:

• drinking too much alcohol or caffeine
• not drinking enough fluids – this can cause strong, concentrated urine to collect in your bladder, which can irritate the bladder and cause symptoms of overactivity
• constipation
• conditions affecting the lower urinary tract (urethra and bladder) – such as urinary tract infections (UTIs) or tumours in the bladder
• neurological conditions
• certain medicines

Causes of overflow incontinence

Overflow incontinence, also called chronic urinary retention, is often caused by a blockage or obstruction affecting your bladder. Your bladder may fill up as usual, but because of an obstruction, you will not be able to empty it completely, even when you try.

At the same time, pressure from the urine that's left in your bladder builds up behind the obstruction, causing frequent leaks. Your bladder can be obstructed by:

• an enlarged prostate gland (if you have a penis)
• bladder stones
• constipation

Overflow incontinence may also be caused by your detrusor muscles not fully contracting, which means your bladder does not completely empty when you urinate. As a result, the bladder becomes stretched. Your detrusor muscles may not fully contract if:

• there's damage to your nerves – for example, as a result of surgery to part of your bowel or a spinal cord injury
• you're taking certain medicines

Causes of total incontinence

Total incontinence is when your bladder cannot store any urine at all. It can mean you either pass large amounts of urine constantly, or you pass urine occasionally with frequent leaking in between. Total incontinence can be caused by:

• a problem with your bladder from birth
• injury to your spinal cord – this can disrupt the nerve signals between your brain and your bladder
• a bladder fistula – a small, tunnel like hole that can form between the bladder and a nearby area, such as the vagina

Medicines that may cause incontinence

Some medicines can disrupt the normal process of storing and passing urine or increase the amount of urine you produce. These include:

• angiotensin converting enzyme (ACE) inhibitors
• diuretics
• some antidepressants
• hormone replacement therapy (HRT)

Stopping these medicines, if advised to do so by a doctor, may help resolve your incontinence.

Risk factors

In addition to common causes, some things can increase your risk of developing urinary incontinence without directly being the cause of the problem. These are known as risk factors. Risk factors for urinary incontinence include:

• increasing age – urinary incontinence becomes more common in middle age and is very common in people who are over 80 years old
• family history – there may be a genetic link to urinary incontinence, so you may be more at risk if other people in your family have the problem
• having lower urinary tract symptoms (LUTS) – a range of symptoms that affect the bladder and urethra