Pelvic inflammatory disease (PID) is caused by an infection developing in the female upper genital tract.

In most cases, the condition is caused by a bacterial infection spreading from the vagina or cervix (entrance to the womb) into the womb, fallopian tubes and ovaries.

PID is often caused by more than one type of bacterium and it can sometimes be difficult for doctors to pinpoint which are responsible.

This means a combination of antibiotics will be prescribed so a variety of bacteria can be treated.

Sexually transmitted infections (STIs)

In about 1 in 4 cases, PID is caused by a sexually transmitted infection (STI) such as chlamydia, gonorrhoea or mycoplasma genitalium.

These bacteria usually only infect the cervix, where they can be easily treated with a single dose of an antibiotic. 

But if they're not treated there's a risk the bacteria could travel into the upper genital tract.

It's estimated 1 in 10 women with untreated chlamydia may develop PID within a year.

Other causes

In many cases, the cause of the infection that leads to PID is unknown.

Sometimes normally harmless bacteria found in the vagina can get past the cervix and into the reproductive organs.

Although harmless in the vagina, these types of bacteria can cause infection in other parts of the body.

This is most likely to happen if:

Which areas can become infected?

If an infection spreads upwards from the vagina and cervix, it can cause inflammation of the:

  • womb lining (endometrium)
  • fallopian tubes
  • tissue around the womb
  • ovaries
  • lining of the inside of the abdomen (peritoneum)

Pockets of infected fluid called abscesses can also develop in the ovaries and fallopian tubes.

Who's most at risk?

Any woman can get PID, but you're more likely to get it if you:

  • have more than 1 sexual partner
  • have a new sexual partner
  • have a history of STIs
  • have had PID in the past
  • are under 25
  • started having sex at a young age