Chlamydia: Symptoms, Causes, Testing and Treatment
The most common bacterial STI in the UK — and one of the most treatable. A complete guide to symptoms, testing, and BASHH 2025 treatment.
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Chlamydia: Symptoms, Causes, Testing and Treatment
What chlamydia is, how it spreads, the symptoms to look for, how to get tested and how it’s treated in the UK.
This is our main chlamydia guide. Looking for treatment? See chlamydia treatment online. Every chlamydia article we publish is listed in our chlamydia guides below.
Get urgent help first. Go to A&E or call 999 for sudden, severe pain in a testicle, or severe pain low in your tummy with a fever, fainting or any chance you could be pregnant. Contact NHS 111 (NHS 24 on 111 in Scotland) or your GP the same day for pelvic pain, pain during sex, bleeding between periods or after sex, or a fever with genital symptoms. Online treatment is not suitable in these situations.
Key fact: Chlamydia is the most commonly diagnosed sexually transmitted infection in England. Most people who have it notice no symptoms, so a test is the only way to know. It’s easily cured with antibiotics.
Tested Positive for Chlamydia? Get Treated Online
Access Doctor is a GPhC-registered pharmacy (#9011198). If you’ve tested positive for chlamydia, or a sexual partner has, a pharmacist independent prescriber reviews your online consultation and prescribes treatment if it’s suitable for you. Dispensed from our UK pharmacy. Approved before 3pm, Monday to Friday? Dispatched the same day, by Royal Mail Tracked 48, Tracked 24 or Special Delivery guaranteed by 1pm next working day: you choose.
Start Chlamydia Consultation →Adults only online. Access Doctor’s online chlamydia service is for adults aged 18 and over who are not pregnant or breastfeeding. If you’re under 18, pregnant or breastfeeding, an NHS sexual health clinic or your GP can test and treat you free and in confidence, and under 25s can also get help from Brook.
What is chlamydia?
Chlamydia is a sexually transmitted infection (STI) caused by the bacterium Chlamydia trachomatis. It lives inside the cells lining the cervix (the neck of the womb), the urethra (the tube you pee through), the rectum, and sometimes the throat or eyes. It’s the most commonly diagnosed STI in England, and diagnoses are highest in people aged 15 to 24 (UKHSA).
Because it usually causes no symptoms, chlamydia can go unnoticed for months and be passed on without anyone knowing. The good news is that it’s easy to test for and easy to cure with a short course of antibiotics.
How chlamydia spreads
Chlamydia is passed on through sex with someone who has it, including:
- vaginal sex and anal sex without a condom;
- oral sex, which can cause infection in the throat;
- sharing sex toys that aren’t washed or covered with a new condom each time;
- genitals touching, even without penetration or ejaculation;
- infected semen or vaginal fluid getting into the eye;
- from a mother to her baby during birth, which can cause eye infection or pneumonia in the baby.
You can’t catch chlamydia from kissing, hugging, sharing towels, cups or cutlery, swimming pools or toilet seats. Using a condom every time you have vaginal, anal or oral sex is the best way to protect yourself.
No symptoms doesn’t mean no infection. You can’t tell whether a partner has chlamydia by looking at them or by whether they feel well. Testing is the only reliable way to know, for both of you.
Symptoms in women and men
Most people with chlamydia have no symptoms. If symptoms do appear, NHS advice is that they can start anywhere from 1 week to several months after infection, or only once the infection has spread.
Symptoms in women
- Pain or stinging when you pee
- Unusual vaginal discharge
- Bleeding after sex or between periods
- Pain during sex, or pain low in your tummy
These are easy to mistake for thrush, a urine infection or period pain. Our guide to chlamydia symptoms in women goes through them in detail.
Symptoms in men
- Pain or stinging when you pee
- White, cloudy or watery discharge from the tip of the penis
- Pain, swelling or tenderness in the testicles
Rectum, throat and eyes
Infection in the rectum (after anal sex) or throat (after oral sex) usually causes no symptoms, though the rectum can become uncomfortable or produce discharge. Infection in the eye can cause redness, pain and discharge (conjunctivitis). Tell whoever tests you about the kinds of sex you’ve had, so the right samples are taken.
Testicle pain needs checking quickly. Pain and swelling in a testicle can mean the infection has spread to the epididymis (the tube behind the testicle). Sudden, severe testicle pain can also be torsion, a twisted testicle, which is an emergency: go to A&E straight away.
Why most people have no symptoms
Chlamydia grows inside the body’s own cells, which helps it avoid triggering the strong inflammation that would make you feel unwell. That’s why it can sit quietly for months. But “quiet” isn’t the same as harmless: an untreated infection can still spread and cause damage, particularly in women. It’s the reason NHS advice is to test regularly rather than waiting for symptoms.
What happens if chlamydia isn’t treated
Most people who are treated promptly have no lasting problems. Left untreated, chlamydia can:
- spread to the womb, fallopian tubes and ovaries in women, causing pelvic inflammatory disease (PID);
- scar the fallopian tubes, which raises the risk of ectopic pregnancy and can make it harder to get pregnant;
- cause epididymo-orchitis, a painful swelling of the testicle and the tube behind it, in men;
- rarely, trigger reactive arthritis, with painful, swollen joints and sometimes sore eyes.
These problems can develop even when the original infection caused no symptoms. Our guide to chlamydia complications explains each one and the warning signs to look out for.
Getting tested
Chlamydia is diagnosed with a laboratory test called a NAAT (nucleic acid amplification test), using a urine sample or a swab. Women usually take a swab from the lower vagina themselves, which is as accurate as one taken by a nurse. Men usually give a urine sample. Swabs from the rectum or throat are used if you’ve had anal or oral sex.
- When: tests are reliable from about 2 weeks after sex. If you test sooner, test again once 2 weeks have passed.
- Who should test: anyone with symptoms, anyone whose partner has chlamydia, anyone who’s had sex without a condom with a new partner, and under 25s who are sexually active, every year and with each new partner.
- Where: free at NHS sexual health clinics across the UK, and with free home kits in many areas. In England, the National Chlamydia Screening Programme offers free tests to young women and other people with a womb aged under 25.
Our chlamydia testing guide covers home kits, clinics, how to take the sample and what your result means.
How chlamydia is treated
Chlamydia is cured with antibiotics. UK guidance from BASHH (the British Association for Sexual Health and HIV) and NICE recommends:
| Antibiotic | Usual course | When it’s used |
|---|---|---|
| Doxycycline | 100mg twice a day for 7 days | First choice for infection of the genitals, rectum or throat |
| Azithromycin | 1g on day 1, then 500mg once a day on days 2 and 3 | For people who can’t take doxycycline, such as those allergic to tetracyclines |
| Other antibiotics | As prescribed | In pregnancy and breastfeeding, a doctor, midwife or clinic chooses a suitable antibiotic, as doxycycline isn’t used |
You may see azithromycin described as a single 1g dose elsewhere. That’s the dose in its product licence, and BASHH’s 2026 guideline also allows it, but NICE CKS and NHS services use the 3-day course above, and so do we. It’s prescribed off-label, which is common, accepted practice in sexual health.
Our guides to doxycycline for chlamydia and azithromycin for chlamydia explain how to take each one and their side effects. If you’re pregnant, see our guide to chlamydia in pregnancy.
You can be treated by an NHS sexual health clinic or your GP, free of charge, or privately through our chlamydia treatment online service if you’re 18 or over, not pregnant or breastfeeding, and have tested positive or a sexual partner has. If you have symptoms of a complication, such as pelvic pain, pain during sex or testicle pain, please see a clinic or your GP instead, as you may need an examination and a different course.
After treatment: sex, partners and retesting
- Sex: don’t have sex, including oral sex and sex with a condom, until you and your partner have both finished treatment and any symptoms have gone. With azithromycin, wait until 7 days after your last tablet.
- Partners: anyone you’ve had sex with in the last 6 months should be tested and treated, even if they feel well. A sexual health clinic can tell them for you without giving your name. See our guide to telling your partners.
- Retesting: if you’re under 25, test again 2 to 6 months after treatment, because catching it again is common (BASHH). Anyone should test again after a new partner.
- Test of cure: not needed routinely. You will need one if you’re pregnant, if your symptoms don’t settle, or if you missed doses; it’s done at least 3 weeks after finishing treatment.
All our chlamydia guides
Each guide is written and reviewed by Dr Abdishakur M Ali (GMC 7041056) against current BASHH, NICE and NHS guidance.
Chlamydia symptoms in women
The signs to look for, what they get mistaken for and when to test.
Read guide →Chlamydia testing in the UK
Free NHS home kits and clinics, when to test and what your result means.
Read guide →Chlamydia complications
PID, ectopic pregnancy, fertility, epididymo-orchitis and reactive arthritis.
Read guide →Doxycycline for chlamydia
The usual first-choice 7-day course: how to take it and side effects.
Read guide →Azithromycin for chlamydia
The alternative for people who can’t take doxycycline.
Read guide →Chlamydia in pregnancy
The risks, which antibiotics are used and the test afterwards.
Read guide →Telling your partners
Who to tell, how far back to go and anonymous options.
Read guide →Azithromycin for other STIs
Mycoplasma genitalium, urethritis and why it isn’t used for gonorrhoea.
Read guide →UK safety, support and free NHS options
Doxycycline and azithromycin are prescription-only medicines in the UK. Before anything is prescribed, a GPhC-registered pharmacist independent prescriber reviews your consultation, including your allergies and the other medicines you take. Always read the patient information leaflet in the pack. Never share antibiotics with anyone else, even a partner with the same infection, and don’t keep leftovers for another time: return unused tablets to a pharmacy.
If you think you’ve had a side effect from a medicine, tell your pharmacist or doctor. You can also report it to the MHRA through the Yellow Card scheme, which helps keep medicines safe for everyone.
NHS sexual health clinics test and treat chlamydia free of charge across the UK, and you don’t need a GP referral: use the NHS website in England, NHS inform in Scotland, Sexual Health Wales in Wales and nidirect in Northern Ireland to find one. Our private chlamydia treatment online service is an alternative for adults aged 18 and over.
If anything about how you got this infection doesn’t feel right, for example if sex wasn’t your choice or a partner pressures or controls you, you can talk to someone in confidence. See support, if you need it for free, confidential helplines. If you’re in immediate danger, call 999.
Frequently Asked Questions
How do you know if you have chlamydia?
You usually can’t tell from how you feel, because most people with chlamydia have no symptoms. The only way to know is a test: a urine sample or a self-taken vaginal swab, plus a rectal or throat swab if you’ve had anal or oral sex. Tests are free at NHS sexual health clinics and through home kits in many areas.
How long can you have chlamydia without knowing?
For months, and sometimes longer. Because it rarely causes symptoms, chlamydia can go unnoticed for a long time while still being passed on and, in some people, causing damage. That’s why regular testing matters, especially if you’re under 25 or have a new partner.
Can chlamydia go away on its own?
Some infections do clear without treatment over months, but there’s no way to know whether yours will, and in the meantime it can be passed on and cause complications. If you test positive, you should always be treated.
Can you get chlamydia more than once?
Yes. Having chlamydia doesn’t make you immune, and catching it again is common, often from a partner who wasn’t treated. That’s why partners should be treated too, and why under 25s are advised to test again 2 to 6 months after treatment.
Can you get chlamydia from oral sex?
Yes. Giving oral sex to someone with chlamydia can cause infection in the throat. Throat infection usually causes no symptoms, so ask for a throat swab if you’ve had oral sex. Doxycycline is the recommended treatment.
Does chlamydia affect fertility?
It can, if it isn’t treated. In women, infection that spreads to the fallopian tubes can scar them, making it harder to get pregnant and raising the risk of ectopic pregnancy. Treating chlamydia early greatly reduces this risk. Whether chlamydia affects fertility in men is less clear.
Can I get treated if my partner has chlamydia but I haven’t tested positive?
Yes. If a sexual partner has been diagnosed with chlamydia, UK guidance is to treat you too, ideally after taking a test, without waiting for your result. Our online service can assess you if you’re 18 or over and not pregnant or breastfeeding.
Is chlamydia the same as gonorrhoea?
No. They’re different bacterial infections that need different treatments, although they cause similar symptoms and often occur together. Most NHS tests check for both from the same sample. Gonorrhoea is treated with an injection at a sexual health clinic.
References
- NHS. Chlamydia. nhs.uk
- British Association for Sexual Health and HIV (BASHH). UK national guideline for the management of infection with Chlamydia trachomatis, 2026 (Saunders J, et al.). doi.org
- NICE Clinical Knowledge Summaries. Chlamydia – uncomplicated genital. cks.nice.org.uk
- UK Health Security Agency. Sexually transmitted infections (STIs): annual data. gov.uk
- UK Health Security Agency. National Chlamydia Screening Programme (NCSP). gov.uk
- NHS. Chlamydia: treatment. nhs.uk
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for diagnosis and treatment. In a medical emergency, call 999.
