PID occurs when bacteria move upward from a woman's vagina or cervix (opening to the uterus) into her reproductive organs. Many different organisms can cause PID, but many
cases are associated with gonorrhea and chlamydia, two very common bacterial STDs. A prior episode of PID increases the risk of another episode because the reproductive organs may be damaged during the initial bout of infection.
Sexually active women in their childbearing years are most at risk, and those under age 25 are more likely to develop PID than those older than 25. This is because the cervix of
teenage girls and young women is not fully matured, increasing their susceptibilty to the STDs that are linked to PID.
The more sex partners a woman has, the greater her risk of developing PID. Also, a woman whose partner has more than one sex partner is at greater risk of developing PID, because of the potential for more exposure to infectious agents.
Women who douche may have a higher risk of developing PID compared with women who do not douche. Research has shown that douching changes the vaginal flora (organisms that live in the vagina) in harmful ways, and can force bacteria into the upper reproductive organs from the vagina.
Women who have an intrauterine device (IUD) inserted may have a slightly increased risk of PID near the time of insertion compared with women using other contraceptives or no
contraceptive at all. However, this risk is greatly reduced if a woman is tested and, if necessary, treated for STDs before an
IUD is inserted.