Chlamydia (kluh-MID-e-uh) is a common sexually transmitted infection (STI), also known as a sexually transmitted disease (STD). Chlamydia is caused by Chlamydia trachomatis (truh-KOH-muh-tis) bacteria. You might not know you have chlamydia because many people don't have symptoms, such as genital pain and discharge from the vagina or penis.

Chlamydia trachomatis affects mostly young women, but it can occur in both men and women and in all age groups. It's not difficult to treat, but if left untreated it can lead to more-serious health problems.

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Early-stage Chlamydia trachomatis infections often cause few symptoms. Even when symptoms occur, they're often mild. That makes them easy to overlook, which is why regular screening is important.

Symptoms of Chlamydia trachomatis infection can include:

  • Painful urination
  • Vaginal discharge
  • Discharge from the penis
  • Painful sexual intercourse in women
  • Vaginal bleeding between periods and after sex
  • Testicular pain

Depending on a person's sexual activity, Chlamydia trachomatis can infect the eyes, throat or rectum. Eye infections, called conjunctivitis, cause the inside of the eyelid to be red and irritated. In the throat, an infection may have no symptoms, or a person may have a sore throat. An infection in the rectum may have no symptoms or may cause rectal pain, discharge or bleeding.

When to see a doctor

See your doctor if you have a discharge from your vagina, penis or rectum, or if you have pain during urination. Also, see your doctor if you learn your sexual partner has chlamydia. Your doctor will likely prescribe an antibiotic even if you have no symptoms.

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The Chlamydia trachomatis bacterium is most commonly spread through vaginal, oral and anal sex. It's also possible for pregnant women to spread chlamydia to their children during delivery, causing pneumonia or a serious eye infection in the newborns.

Risk factors

Risk factors for chlamydia include:

  • Less condom use.
  • Less use of health services to prevent and treat sexually transmitted infections.
  • Multiple sex partners.
  • Changing sex partners before learning about a chlamydia infection.

People who have sex before age 25 are at higher risk of chlamydia than are older people. That's because younger people are more likely to have more than one risk factor.


Chlamydia trachomatis can be associated with:

  • Pelvic inflammatory disease (PID). PID is an infection of the uterus and fallopian tubes that causes pelvic pain and fever. Severe infections might require hospitalization for intravenous antibiotics. PID can damage the fallopian tubes, ovaries and uterus, including the cervix.
  • Infection near the testicles (epididymitis). A chlamydia infection can inflame the coiled tube located beside each testicle (epididymis). The infection can result in fever, scrotal pain and swelling.
  • Prostate gland infection. Rarely, the chlamydia organism can spread to the prostate gland. Prostatitis can cause pain during or after sex, fever and chills, painful urination, and lower back pain.
  • Infections in newborns. The chlamydia infection can pass from the vaginal canal to your child during delivery, causing pneumonia or a serious eye infection.
  • Ectopic pregnancy. This occurs when a fertilized egg implants and grows outside of the uterus, usually in a fallopian tube. The pregnancy needs to be removed to prevent life-threatening complications, such as a burst tube. A chlamydia infection increases this risk.
  • Infertility. Chlamydia infections — even those that produce no signs or symptoms — can cause scarring and obstruction in the fallopian tubes, which might make women infertile.
  • Reactive arthritis. People who have Chlamydia trachomatis are at higher risk of developing reactive arthritis, also known as Reiter syndrome. This condition typically affects the joints, eyes and urethra — the tube that carries urine from your bladder to outside of your body.


The surest way to prevent chlamydia infection is to abstain from sexual activities. Short of that, you can:

  • Use condoms. Use a male latex condom or a female polyurethane condom during each sexual contact. Condoms used properly during every sexual encounter reduce but don't eliminate the risk of infection.
  • Limit your number of sex partners. Having multiple sex partners puts you at a high risk of contracting chlamydia and other sexually transmitted infections.
  • Get regular screenings. If you're sexually active, particularly if you have multiple partners, talk with your doctor about how often you should be screened for chlamydia and other sexually transmitted infections.
  • Avoid douching. Douching decreases the number of good bacteria in the vagina, which can increase the risk of infection.

April 14, 2023
  1. WHO guidelines for the treatment of Chlamydia trachomatis. World Health Organization. https://www.who.int/reproductivehealth/publications/rtis/chlamydia-treatment-guidelines/en/. Accessed Jan. 13, 2020.
  2. Cohen J, et al., eds. Chlamydia trachomatis infection. In: Infectious Diseases. 4th ed. Elsevier; 2017. https://www.clinicalkey.com. Accessed Jan. 13, 2020.
  3. AskMayoExpert. Chlamydia, gonorrhea, and nongonococcal urethritis. Mayo Clinic; 2019.
  4. Chlamydia: CDC fact sheet (detailed). Centers for Disease Control and Prevention. https://www.cdc.gov/std/chlamydia/stdfact-chlamydia-detailed.htm. Accessed Jan. 4, 2020.
  5. Chlamydial infections. Centers for Disease Control and Prevention. https://www.cdc.gov/std/treatment-guidelines/chlamydia.htm. Accessed March 31, 2023.


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Chlamydia trachomatis