Chlamydia is usually passed from one person to another during sex. You can become infected with chlamydia if you come into contact with the semen or vaginal fluids of someone who already has the infection.
The bacteria can live inside the cells of the cervix (entrance to the uterus – womb), the urethra (tube where urine comes out), the rectum (back passage) and sometimes the throat and eyes.
The infection is most commonly spread through:
unprotected vaginal, anal or oral sex
sharing sex toys if you don’t wash them or cover them with a new condom each time they’re used.
Infected semen or vaginal fluid coming into contact with the eye can cause conjunctivitis.
Chlamydia can also be passed from a pregnant woman to her baby (see below, What happens if I get chlamydia when I’m pregnant?)
It is not yet clear if chlamydia can be spread by transferring infected semen or vaginal fluid to another person’s genitals on the fingers or through rubbing vulvas (female genitals) together.
You cannot catch chlamydia from kissing, hugging, sharing baths or towels, swimming pools, toilet seats or from sharing cups, plates or cutlery.