Chlamydia is a common sexually transmitted infection (STI) caused by Chlamydia trachomatis. It can affect the cervix, urethra, rectum and throat. Many infections cause no symptoms, which is why testing is important for people who may have been exposed.
Possible symptoms
- Unusual vaginal or penile discharge
- Burning or pain when urinating
- Bleeding between periods or after sex
- Lower abdominal or pelvic pain
- Pain or swelling in one or both testicles
- Rectal pain, discharge or bleeding
Symptoms may appear several weeks after exposure, but an infection can be present without any noticeable symptoms.
How chlamydia spreads
Chlamydia can spread through vaginal, anal or oral sex with an infected partner. It can also pass from a pregnant person to a baby during childbirth. Condoms and other barrier methods reduce the risk when used correctly.
Testing
Chlamydia is usually diagnosed with a nucleic acid amplification test (NAAT). Depending on anatomy and sexual exposure, testing may use a vaginal swab, first-catch urine, or a swab from the rectum or throat. Testing for other STIs, including Gonorrhea, Syphilis and HIV, may also be appropriate.
Treatment
Chlamydia can be cured with antibiotics. Treatment should be started promptly and taken exactly as prescribed. The appropriate antibiotic can depend on factors such as pregnancy, infection site and individual medical circumstances.
To reduce transmission and reinfection, follow the clinician’s instructions about when sexual activity can safely resume. Sexual partners may also need evaluation and treatment. Reinfection is common, so repeat testing about three months after treatment is generally recommended.
Pregnancy
Chlamydia during pregnancy requires appropriate antibiotic treatment and follow-up. A test of cure is generally recommended about four weeks after treatment during pregnancy, followed by repeat testing according to clinical guidance.
Possible complications
Untreated chlamydia can lead to pelvic inflammatory disease, ectopic pregnancy and fertility problems. In men, infection can sometimes cause epididymitis, with pain and swelling around a testicle.
When to seek urgent medical care
Seek urgent medical assessment for severe pelvic or abdominal pain, fainting, heavy bleeding, high fever with worsening illness, or sudden severe testicular pain. Severe pain with a possible pregnancy also needs urgent assessment.
Related topics
Sources and Further Reading
Last reviewed: 4 September 2026