If chlamydia is left untreated in a woman, it can spread to the womb, fallopian tubes, and ovaries. This is a common cause of pelvic inflammatory disease (PID), which can lead to difficulty getting pregnant and an increased risk of ectopic pregnancy.
In men, chlamydia can cause inflammation of the testicles and in some cases a form of arthritis, known as sexually acquired reactive arthritis (SARA).