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Causes - Cystitis

Cystitis is usually caused by a bacterial infection. It sometimes happens when the bladder is irritated or damaged for another reason.

Cystitis caused by bacterial infections

Most infections are thought to occur when bacteria in the bowel or on the skin get into the bladder via the urethra. The urethra is the tube that removes urine from the bladder and out of the body.

Women may get cystitis more than men because their anus is closer to their urethra, which is much shorter. This means bacteria could get into the bladder more easily.

It's not always obvious how the bacteria get into the bladder. But some things can increase the risk of it happening, including:

  • having sex
  • wiping your bottom after going to the toilet – particularly if you wipe from back to front
  • inserting a tampon or urinary catheter (a tube that empties the bladder)
  • using a diaphragm for contraception

Things that increase your risk of bladder infection

Not being able to empty your bladder

If you cannot empty your bladder, bacteria that get inside might not be flushed out when you go to the toilet. They can then multiply more easily.

You may not be able to empty your bladder if:

  • you have a blockage in your urinary system, such as a narrowing of the urethra (water passage)
  • you're pregnant (the baby may be pressing on your bladder)
  • you have an enlarged prostate gland that presses on the urethra


The lining of the urethra can shrink for women who have been through or are going through the menopause. This is due to a lack of oestrogen.

The natural balance of bacteria in the vagina may change. This can allow harmful bacteria to become more common.

This can make the urethra more prone to infection, which could then spread to the bladder.


You're more likely to get cystitis if you have diabetes. This is a condition where the level of sugar in your body becomes too high.

High levels of sugar in your pee can provide a good environment for bacteria to multiply. If bacteria then get into the bladder, they're more likely to cause cystitis.

Other causes of cystitis

Damage or irritation to the urethra and bladder can cause cystitis.

This can be the result of:

  • friction from sex
  • chemical irritants, such as those in perfumed soap or bubble bath
  • damage caused by a catheter or surgery on your bladder
  • radiotherapy to your pelvis or treatment with certain chemotherapy medicines
  • a woman's genitals being cut or changed for cultural, religious or social reasons. This is an illegal practice called female genital mutilation or FGM.

Cystitis has also been linked to the use of the drug ketamine.

Content supplied by the NHS and adapted for Ireland by the HSE

Page last reviewed: 22 March 2021
Next review due: 22 March 2024

This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.