Urinary tract infection - Causes of a urinary tract infections

Most urinary tract infections (UTIs) are caused by bacteria that live in the digestive system.

If these bacteria get into the urethra (the tube where urine comes out), they can cause infection.

It's thought the bacteria can spread to the urethra via the anus. For example, if toilet paper touches your anus and then touches your genitals, the bacteria can multiply and move through your urinary tract, causing infection of your:

urethra (urethritis)
bladder (cystitis)
ureters (ureteritis) – the ureters are tubes that run from the bladder to the kidneys
kidneys (pyelonephritis)

Who's at risk of getting a UTI?

Women are more likely than men to have a UTI. This is because in women, the urethra is closer to the anus than it is in men. Also, the urethra is much shorter in women, making it easier for bacteria to reach the bladder.

You are also more likely to develop a UTI if you have:

a condition that obstructs or blocks your urinary tract, such as kidney stones
a condition that prevents you fully emptying your bladder (it's easier for bacteria to multiply if urine stays in the bladder for too long)
a weakened immune system – from chemotherapy or HIV, for example
a urinary catheter – a tube inserted into your bladder to drain away the urine

Further risk factors in women

Women are also more likely to get a UTI if:

they're sexually active – having sex can irritate the urethra, allowing bacteria to travel through it more easily and into the bladder
they use a diaphragm for contraception, as a diaphragm can put pressure on the bladder and prevent it emptying properly
they use condoms coated in spermicide, as spermicide can irritate the vagina, making it more vulnerable to infection

Further risk factors in men

Men are also more likely to get a UTI if:

they have an enlarged prostate gland – this can put pressure on the bladder and urethra, preventing the bladder emptying properly

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