Quick answer
What is chlamydia?
Chlamydia is a bacterial sexually transmitted infection — often no symptoms but can cause pain when urinating, discharge, and pelvic pain. Untreated chlamydia can lead to infertility in women and epididymitis in men. Diagnosed with urine test or swab; treated with a short course of antibiotics (usually doxycycline or azithromycin). Free confidential testing via NHS sexual health clinics and postal kits. Tell recent partners so they can be tested and treated.
Chlamydia — the silent common STI
Chlamydia (Chlamydia trachomatis) is the most commonly diagnosed sexually transmitted infection (STI) in the UK — especially among under-25s. It is a bacterial infection passed through unprotected vaginal, anal, or oral sex.
The problem: most people have no symptoms — infection persists, spreads to partners, and causes serious complications unless found by testing.
Symptoms — when they occur
Women:
- pain when urinating
- unusual vaginal discharge
- bleeding between periods or after sex
- pain during sex
- lower abdominal pain — may indicate pelvic inflammatory disease (PID)
Men:
- white, cloudy, or watery discharge from penis
- pain when urinating
- testicular pain or swelling — epididymitis
Both:
- rectal pain or discharge — anal infection
- sore throat — pharyngeal infection (usually asymptomatic)
Up to 70% of women and 50% of men — no symptoms at all.
Complications if untreated
| Population | Complication |
|---|---|
| Women | Pelvic inflammatory disease (PID) — chronic pain, infertility, ectopic pregnancy |
| Men | Epididymo-orchitis — testicular inflammation, fertility impact |
| Both | Reactive arthritis (rare) |
| Pregnancy | Pass to baby — neonatal conjunctivitis, pneumonia |
Damage to fallopian tubes is often irreversible — early testing matters.
Testing
Free, confidential in England:
- sexual health (GUM) clinics
- NHS postal test kits online for under-25s and high-risk groups
- some GP surgeries and pharmacies
Samples:
- first-catch urine (men and women — not mid-stream)
- self-taken vaginal swab (women)
- throat and rectal swabs if relevant exposure — ask explicitly
Results in days to two weeks.
Routine screening: sexually active under-25s advised annual test or on new partner.
Treatment
First-line (BASHH guidelines):
- Doxycycline 100mg twice daily for 7 days
Alternatives:
- Azithromycin — single-dose or short course — used in pregnancy or doxycycline intolerance (doxycycline avoided in pregnancy)
Important:
- complete full course
- avoid sex 7 days after you and partner(s) treated
- retest at 3 months — high reinfection rate in young people
Allergies — tell clinician for alternative regimens.
Partner notification
Tell all partners within last 6 months (or last partner if longer) — clinic can notify anonymously.
Untreated partner = reinfection for you.
Pregnancy and chlamydia
Screen all pregnant women — chlamydia linked to preterm birth and neonatal infection.
Treatment in pregnancy — azithromycin (not doxycycline).
Prevention
- condoms — reduce but do not eliminate risk
- regular testing with new partners
- PrEP does not prevent chlamydia — separate STI testing still needed
Chlamydia vs other discharge causes
| Condition | Clues |
|---|---|
| Thrush | Itching, thick white discharge — not STI |
| Bacterial vaginosis | Fishy odour, grey discharge |
| Gonorrhoea | Often more purulent discharge; co-infection common — dual testing standard |
| UTI | Urinary symptoms without sexual exposure |
Clinics test chlamydia and gonorrhoea together routinely.
After treatment
- symptoms improve in days
- PID or epididymitis may need longer follow-up
- fertility concerns after past PID — GP or fertility clinic if struggling to conceive after 12 months trying
Chlamydia is easy to test, easy to treat, dangerous to ignore. If you are sexually active with new or multiple partners — get tested even without symptoms.
Common questions
- How do I know if I have chlamydia?
- You often cannot without a test — most infections are asymptomatic. Possible signs — pain when urinating, unusual discharge from penis or vagina, bleeding between periods or after sex, pain during sex, or testicular pain. Free confidential tests available from sexual health clinics and NHS online postal services.
- How is chlamydia treated?
- First-line is doxycycline 100mg twice daily for 7 days. Alternative azithromycin single-dose course in some situations (pregnancy, intolerance). Antibiotics cure the infection — finish the course. Retest 3 months later as reinfection is common.
- Can chlamydia go away on its own?
- Occasionally clears without treatment but should never be relied on — untreated chlamydia causes serious complications including infertility, ectopic pregnancy, and chronic pain. Always treat when diagnosed.
- How long after treatment can I have sex?
- Avoid all sex (including oral and anal) for 7 days after you and your partner(s) complete treatment, or until 7 days after a single-dose azithromycin — prevents reinfection. Use condoms with new partners to reduce risk.
- Does chlamydia cause infertility?
- Yes — untreated chlamydia can scar fallopian tubes in women (infertility, ectopic pregnancy risk) and cause epididymo-orchitis in men affecting fertility. Early treatment prevents most complications — damage already done may be irreversible.
- Can I get chlamydia from oral sex?
- Yes — chlamydia infects throat, rectum, penis, and cervix. Different sites may need different swabs — tell the clinic about all types of sex for complete testing.
- Should I tell previous partners?
- Yes — sexual health services offer anonymous partner notification. Recent partners (within 6 months or last partner) should be tested and treated. Prevents reinfection and protects their health.