Chlamydia (kluh-MID-e-uh) trachomatis (truh-KOH-muh-tis) is a common sexually transmitted infection (STI) caused by bacteria. You may not know you have chlamydia because many people never develop the signs or symptoms, such as genital pain and discharge from the vagina or penis.
Chlamydia trachomatis affects both men and women and occurs in all age groups, though it's most prevalent among young women. Chlamydia isn't difficult to treat once you know you have it. If left untreated, however, it can lead to more-serious health problems.