The facts on this common STD.
Chlamydia is an infection caused by the bacterium Chlamydia trachomatis. It's one of the most widespread of all sexually transmitted diseases, according to the Centers for Disease Control and Prevention.
Chlamydia can be transmitted during vaginal or anal sex when one partner is infected. It can also be passed on to the eye by a hand moistened with infected secretions, and to a newborn from an infected mother during delivery. It's possible, but rare, to pass chlamydia to the throat through an act of oral sex with an infected man.
Symptoms usually show up one to three weeks after infection, if they appear at all. According to the American Social Health Association (ASHA), men are much more likely to have symptoms than women.
If a man does have symptoms, it's usually a burning sensation when urinating, especially the first time in the morning, and a discharge from the penis. The most common symptom for women is increased vaginal discharge; less common are painful urination, unusual vaginal bleeding, bleeding after sex, and lower abdominal pain.
According to ASHA, unchecked and untreated chlamydia can lead to many problems. In men, the epididymis -- the region of the male genitals where sperm mature -- can become infected. Women can get pelvic inflammatory disease, an infection of the upper genital tract that can lead to scarring of the fallopian tubes. The scarring can increase a woman's risk of ectopic pregnancy, chronic pelvic pain, and infertility.