Chlamydia
Symptoms, Causes & Treatment
Everything you need to know about chlamydia: why it is so often missed, what complications it causes, and how to get tested and treated online.
What Is Chlamydia?
Chlamydia is a bacterial sexually transmitted infection (STI) caused by Chlamydia trachomatis. It is the most commonly diagnosed bacterial STI in the UK, with over 150,000 cases reported annually, though the true number is significantly higher because chlamydia is frequently asymptomatic.
Chlamydia is particularly prevalent among young adults aged 15–24, which is why the National Chlamydia Screening Programme (NCSP) recommends annual screening for all sexually active people in this age group.
The infection most commonly affects the genital tract (cervix in women, urethra in men) but can also infect the rectum, throat, and eyes. Left untreated, chlamydia can cause serious complications including pelvic inflammatory disease (PID), tubal damage, ectopic pregnancy, and infertility in women, and epididymo-orchitis in men.
Chlamydia is easily diagnosed with a simple test and is curable with a short course of antibiotics. Early detection and treatment prevent complications and onward transmission.
What Are the Symptoms of Chlamydia?
Most chlamydia is completely silent. When symptoms occur, they appear 7–21 days after exposure.
Most chlamydia is asymptomatic (70–80% of women, 50% of men) · Discharge from penis or vagina · Burning urination · Pelvic pain or deep pain during sex · Testicular pain or swelling · Rectal symptoms (discharge, pain) in receptive anal sex
Pelvic inflammatory disease (PID) — pelvic pain, fever, deep dyspareunia · Epididymo-orchitis — testicular swelling and pain · Reactive arthritis (Reiter's syndrome) — joint pain, eye inflammation after chlamydia · Ectopic pregnancy risk from tubal scarring
If chlamydia symptoms are accompanied by fever and severe pelvic pain, this suggests PID or systemic infection requiring same-day assessment. In men, severe testicular pain and swelling with fever suggests epididymo-orchitis — attend A&E or urgent care that day.
What Causes Chlamydia?
Chlamydia is the most common bacterial STI in the UK. Understanding why it is so common — largely because it is asymptomatic — explains the importance of regular screening.
Chlamydia trachomatis is the most common bacterial STI in the UK, with over 200,000 diagnoses annually. It primarily infects columnar epithelial cells of the urethra, cervix, rectum, and conjunctiva.
Untreated chlamydia causes PID in 10–15% of infected women. PID damages the fallopian tubes, causing tubal factor infertility, chronic pelvic pain, and 6–10x increased ectopic pregnancy risk.
STIs are transmitted through unprotected vaginal, anal, or oral sex. Some (herpes, HPV, syphilis) can spread through skin-to-skin contact even without penetration or visible symptoms.
Many STIs, particularly chlamydia, gonorrhoea, and early HIV, cause no symptoms at all. Regular testing is the only way to detect them — waiting for symptoms means delayed treatment and onward transmission.
Condoms reduce STI transmission by 85–98% when used consistently and correctly. They are less effective for infections spread by skin contact (herpes, HPV, syphilis) where lesions extend beyond the condom-covered area.
STI co-infection is common. Gonorrhoea and chlamydia frequently co-exist (15–40% co-infection rate). HIV significantly increases susceptibility to all other STIs and their complications.
Key Risk Factors
How Is Chlamydia Diagnosed?
Chlamydia is diagnosed by NAAT test — the most sensitive available. A urine sample (men and women), vaginal swab (self-collected or clinician-taken), or rectal/pharyngeal swab depending on exposure history. Results are usually available within 2 weeks. Postal testing kits are available free from NHS online services.
How Is Chlamydia Treated?
Chlamydia is completely curable with a short antibiotic course. Treatment is straightforward and highly effective when taken correctly.
Supportive Measures
Complete the full 7-day doxycycline course. Abstain from sex until you and all partners have finished treatment. All partners in the past 6 months should be tested and treated. Do not re-test for cure unless the pharynx or rectum was treated. Re-test 3 months after treatment if ongoing risk exists.
Chlamydia Reinfection
Chlamydia does not confer lasting immunity — reinfection is common, particularly among under-25s. After treatment, a test of cure is not routinely recommended (unless rectal or pharyngeal site), but re-testing 3 months after treatment is advised if risk factors persist. Partner notification is essential to prevent ping-pong reinfection.
When Should You Get Tested for Chlamydia?
Severe pelvic pain with fever — possible PID or tubo-ovarian abscess · Testicular swelling with severe pain — possible epididymo-orchitis (same-day assessment needed) · Known PID with clinical deterioration.
You are under 25 and sexually active · You have had a new sexual partner · A partner has tested positive for chlamydia · You have symptoms of chlamydia · You want a postal chlamydia test.
How to Prevent Chlamydia
Chlamydia is largely preventable through regular screening, consistent condom use, and prompt treatment when detected.
The NCSP (National Chlamydia Screening Programme) offers annual postal chlamydia testing for all sexually active under-25s in England. Kits can be ordered free from SHGM. Early detection prevents PID and infertility.
Annual STI testing is recommended for all sexually active people. Those with multiple partners should test every 3 months. Free NHS testing is available at sexual health clinics, online via SHGM/SH:24, and from GP surgeries.
Use condoms consistently for vaginal, anal, and oral sex with new or casual partners. Dental dams reduce transmission during oral-vulval contact. Lube reduces condom breakage and anal mucosal trauma.
Notify all recent sexual partners when diagnosed with an STI so they can be tested and treated. Partner notification can be done directly or anonymously through the sexual health clinic (contact tracing service).
HPV vaccination prevents 90% of cervical cancer and most genital warts. Hepatitis B vaccine is recommended for all MSM, PWID, and sexual health clinic attendees not previously vaccinated.
PrEP (Truvada or Descovy) is available free on the NHS at sexual health clinics for eligible high-risk individuals. It is over 99% effective when taken as prescribed. Regular HIV and kidney function testing is required during use.
Speak to a Clinician About Chlamydia Testing
Through The GP Service, a clinician can arrange chlamydia testing, prescribe doxycycline, and advise on partner notification — all from home, quickly and confidentially.
Expert clinical advice, when you need it.
Chlamydia FAQs
Without treatment, chlamydia can persist silently for months or years, causing progressive damage to the reproductive tract. In women, untreated chlamydia causes pelvic inflammatory disease (PID) in 10–15% of cases, leading to tubal factor infertility, chronic pelvic pain, and ectopic pregnancy risk increased 6–10-fold. In men, chlamydia causes epididymo-orchitis, which can impair sperm production and quality. Reactive arthritis (formerly Reiter's syndrome) — involving joint inflammation, eye inflammation, and urethritis — is a rare but recognised complication. These complications are entirely preventable with prompt diagnosis and a simple 7-day course of doxycycline.
STI testing is recommended annually for all sexually active people. Those with new or multiple partners should test every 3 months. Testing is free at NHS sexual health clinics and from online services (SH:24, SHGM). You do not need symptoms to be tested — most STIs cause no symptoms. A full STI screen covers chlamydia, gonorrhoea, syphilis, HIV, hepatitis B, and hepatitis C. Specific sites tested (urine, swabs, blood) depend on your sexual practices. Results are usually available within 1–2 weeks. Positive results trigger automatic partner notification advice.
Not all STIs are curable, but all are treatable. Bacterial STIs — chlamydia, gonorrhoea, and syphilis — are fully curable with antibiotics when diagnosed promptly. Viral STIs — HIV, herpes, HPV, and hepatitis B — cannot be cured but can be effectively managed. HIV is controlled with ART to the point of undetectability. Herpes is managed with antivirals that suppress outbreaks. HPV often clears naturally within 1–2 years in people with healthy immune systems. Genital warts can be treated and removed, though the underlying HPV virus may persist. The key message: all STIs are manageable with prompt diagnosis and treatment.
Yes. HIV is now a manageable chronic condition, not a death sentence. With antiretroviral therapy (ART), people with HIV can live long, healthy lives with a normal life expectancy. ART suppresses the virus to undetectable levels in the blood, meaning it cannot be transmitted sexually (Undetectable = Untransmittable, or U=U). Most people on modern ART take a single tablet daily and experience minimal side effects. HIV does not prevent you from having children, working, or having a fulfilling life. In the UK, HIV care is excellent and free on the NHS. The biggest barrier to good outcomes is late diagnosis — testing early is life-saving.
PEP (post-exposure prophylaxis) is a 28-day course of antiretroviral drugs that prevents HIV infection after a potential exposure. It must be started within 72 hours — the sooner the better. PEP is available from A&E departments, sexual health clinics, and some GUM clinics 24/7. It is free on the NHS for NHS patients. PEP is not a substitute for PrEP or condoms and should be used only in genuine emergencies (unprotected sex with a known HIV-positive person not on suppressive ART, condom failure, sexual assault, or needlestick). After completing PEP, an HIV test at 45 days and 3 months confirms whether infection was prevented.
Yes, but safely. With modern antiviral suppression, the risk of transmitting herpes to a partner is substantially reduced. Daily suppressive valaciclovir reduces transmission risk by approximately 50%, combined with condom use. Disclosing herpes to a new partner is an important conversation — most people with herpes have had it from a previous partner without knowing. Your sexual health clinician can help with disclosure conversations and partner testing. Most people with herpes continue to have satisfying, loving relationships. Herpes is extremely common — HSV-2 affects around 1 in 6 adults — and carries significant social stigma disproportionate to its medical impact.
Gonorrhoea is increasingly difficult to treat due to rising antibiotic resistance. The current UK first-line treatment is a single intramuscular injection of ceftriaxone 1g. A test of cure is required 2 weeks later to confirm eradication. Azithromycin is no longer recommended routinely due to resistance. Multidrug-resistant gonorrhoea has been identified in multiple countries, including the UK. If you have been treated for gonorrhoea and symptoms persist, return to the clinic immediately — do not take additional antibiotics without guidance. Treatment of all recent sexual partners is essential to prevent reinfection.
Syphilis in pregnancy can cause miscarriage, stillbirth, premature birth, and severe congenital syphilis in the newborn (causing bone, liver, brain, and skin disease). All pregnant women in the UK are offered a syphilis blood test at their first antenatal appointment. Treatment with benzathine penicillin G during pregnancy is safe and highly effective at preventing mother-to-child transmission. If you are pregnant and believe you may have been exposed to syphilis, seek urgent testing and treatment. Contact tracing of all recent partners is mandatory. Untreated syphilis in pregnancy is one of the most preventable causes of neonatal death.