Urinary incontinence occurs when the normal process of storing and passing urine is disrupted. This can happen for a number of reasons, and certain factors may also increase your chance of developing urinary incontinence.
How you normally pass urine
The process for creating, storing and passing urine involves the following steps:
- Your kidneys, two bean-shaped organs located just underneath your ribcage, filter your blood and turn the waste products into urine.
- The urine passes down two tubes, called ureters, which run from your kidneys to your bladder.
- Your bladder stores the urine until it is full, stretching like a balloon as it fills up.
- Your pelvic floor muscles, which support the bladder and urethra (tube that carries urine from the bladder to outside the body), help hold the urethra closed and prevent any urine from being passed until you decide to do so.
- When your bladder is full, a nerve signal is sent from your bladder to your brain, which lets you know that you need to pass urine.
- When you get to a toilet, another nerve signal is sent from your brain to your urethra, which relaxes at the same time as your bladder contracts. This allows urine to be emptied out of your bladder through your urethra
The various causes and risk factors of urinary incontinence are explained below.
Causes of stress incontinence
Stress incontinence happens when the pressure in your bladder as it fills with urine becomes greater than the strength of your urethra to stay closed. Your urethra may not be able to stay closed if:
- your pelvic floor muscles are weak or damaged
- your urethral sphincter (the ring of muscles that keeps the urethra closed) is damaged
Any sudden extra pressure on your bladder, such as laughing or sneezing, can cause urine to leak out of your urethra. The loss of strength in your urethra may be caused by:
- nerve damage during childbirth
- increased pressure on your tummy, for example because you are pregnant or very overweight (morbidly obese)
- a problem with the supporting tissues, such as a problem with your collagen, a type of protein found throughout the body, which could make the tissues weaker
- a lack of the hormone oestrogen in women (less oestrogen is produced after the menopause, when a woman’s periods stops)
- certain medications (see box, left)
Causes of urge incontinence
Urge incontinence can be accompanied by overactive bladder syndrome (OAB), a condition that causes an urgent need to pass urine, often frequently and during the night.
The urgent and frequent need to pass urine can be caused by the muscles in the walls of the bladder, known as the detrusor muscles. 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 called detrusor overactivity. The reason your detrusor muscles contract too often may not be clear, but possible causes include:
- conditions affecting the lower urinary tract (urethra and bladder), such as urinary tract infections (UTIs) or tumours in the bladder
- neurological conditions, which affect the brain and spinal cord, such as Parkinson’s disease or multiple sclerosis
- conditions that affect the whole body, such as diabetes, a condition caused by too much glucose in the blood
- conditions or behaviour that affect the way your digestive system functions, such as drinking too much alcohol or caffeine (found in tea, coffee and cola) or constipation
- certain medications (see box, left)
Some other factors related to OAB include:
Some of these possible causes will lead to short-term urinary incontinence, and others may cause long-term urinary incontinence. If the cause can be treated, this may cure your incontinence. For example, a UTI can be treated with medication or constipation can be managed by changing your diet.
Causes of overflow incontinence
Overflow incontinence, also called chronic urinary retention, is often caused by a blockage or obstruction to your bladder. Your bladder may fill up as usual, but as it is obstructed you will not be able to empty it completely even when you try.
At the same time, pressure from the urine that is still in your bladder builds up behind the obstruction, causing frequent leaks.
Your bladder can become obstructed by:
- an enlarged prostate gland in men - the prostate gland is located between the penis and the bladder and can get larger as men get older
- bladder stones - small, stone-like lumps that can form in your bladder
- constipation - a build-up of faeces can obstruct your bladder if you are unable to completely empty your bowels
Overflow incontinence may also be caused by your detrusor muscles not fully contracting, which means that your bladder does not completely empty when you go to the toilet. As a result, the bladder becomes stretched. Your detrusor muscles may not fully contract if:
- there is damage to your nerves, for example as a result of surgery to part of your bowel or a spinal cord injury
- you are taking certain medications (see box, left)
Causes of total incontinence
Total incontinence occurs when your bladder cannot store any urine at all. It can result in you either passing large amounts of urine constantly, or passing urine occasionally with frequent leaking.
Total incontinence can be caused by:
- a problem with your bladder from birth
- injury to your spinal cord, which can disrupt the nerve signals between your brain and your bladder (see the Health A-Z topic about Paralysis for more information about spinal cord injuries)
- a bladder fistula, which is a small, tunnel-like structure that can develop between the bladder and a nearby area, such as a woman's vagina
Risk factors
Risk factors are not the same as causes. Risk factors are things that increase your chance of developing a condition. However, a risk factor will not definitely cause the condition.
You can reduce some risk factors, such as obesity, through changing your lifestyle.
Risk factors in women
Risk factors for urinary incontinence in women include:
- pregnancy - if you developed stress incontinence during pregnancy or in the six weeks after the birth, you are more likely to have stress incontinence five years after the birth
- vaginal birth - giving birth vaginally, rather than with a caesarean, may be associated with stress incontinence
- heavier birth weight - having a child or children who were heavier than normal at birth is associated with developing urinary incontinence
- number of children - giving birth to a high number of children may be associated with urinary incontinence
- obesity - having a body mass index (BMI) of 30 or more may also be associated with urinary incontinence (use the healthy weight calculator to work out your BMI)
- family history - there may be a genetic link to urinary incontinence, particularly stress incontinence
- increasing age - urinary incontinence becomes more common as you reach middle age and is most common in women over 70 years of age
- lower urinary tract symptoms (LUTS) - symptoms that affect the bladder and urethra (see Urinary incontinence - symptoms for more information)
The menopause, when a woman’s periods stop, is not a risk factor for urinary incontinence. Most evidence suggests that a hysterectomy, an operation to remove the womb, is also not a risk factor for urinary incontinence.
Risk factors in men
Risk factors for urinary incontinence in men include:
- increasing age - urinary incontinence becomes more common as you get older
- family history - there may be a genetic link to urinary incontinence, particularly stress incontinence
- neurological disorders - conditions affecting your brain and spinal cord, such as multiple sclerosis, may increase your risk of urinary incontinence
- prostatectomy - an operation to remove your prostate gland, for example if you have prostate cancer, may increase your risk of urinary incontinence
- functional and cognitive impairment - if your ability to look after yourself or to think or concentrate is affected, for example because of a condition such as dementia, you may be at increased risk of urinary incontinence
- lower urinary tract symptoms (LUTS) - symptoms that affect the bladder and urethra (see Urinary incontinence - symptoms for more information)
Smoking and diet are also possible risk factors for urinary incontinence in both men and women.
