Chlamydia
Chlamydia is the most commonly diagnosed sexually transmitted infection (STI) in the UK, caused by the bacterium Chlamydia trachomatis. It is particularly prevalent among sexually active people under 25.
Most people with chlamydia experience no symptoms, which is why testing is so important. When symptoms do occur, they may include unusual discharge, pain when urinating and, in women, bleeding between periods or after sex.
If left untreated, chlamydia can lead to serious complications including pelvic inflammatory disease (PID) in women, which can cause fertility problems, and epididymitis in men. Chlamydia can also be transmitted during pregnancy and may affect the newborn.
Testing is straightforward, using a urine sample or swab from the affected site (genital, rectal or throat). Chlamydia is easily treated with antibiotics. Regular testing is recommended for those with new or multiple sexual partners.
Causes of Chlamydia
Chlamydia is caused by infection with the bacterium Chlamydia trachomatis. It is transmitted through unprotected vaginal, anal or oral sex, and can also be passed from mother to baby during childbirth.
Factors that increase the risk of infection include:
- Being under 25, the age group with the highest rates of chlamydia in the UK
- Having a new sexual partner or multiple partners
- Not using barrier contraception (condoms) consistently
- Having a partner who has chlamydia or another STI
Because chlamydia is usually asymptomatic, many people unknowingly carry and transmit the infection. The NHS recommends annual screening for sexually active people under 25 and testing whenever a new sexual partner is involved.
Tests that can help check this condition
Learn more on the official NHS page .
Medical review
Dr. Shahzaib Ahmad MBBS, BSc, MRCP, FRCA, FFICM
Clinical Supervisor - Vitall|GMC 7495062|Profile
Reviewed on 22/05/2026
Next review due 22/05/2027
Review focus: Blood biomarkers, laboratory testing methodology, and biochemical interpretation.
