Chlamydia is a common sexually transmitted infection (STI) that is usually passed on by having unprotected sex. It’s also known as chlamydia trachomatis, which is the name of the bacteria that causes it.

By Wallace Health I Medically reviewed by Adrian Roberts.
Page last reviewed: October 2018 I Next review due: October 2023

What is chlamydia?

Chlamydia affects men and women. It’s the most common STI in the UK, especially among sexually active women under 25. In every 100 sexually active young people, three to seven have chlamydia.

In women, it can affect the area around the cervix (entrance to the womb) or the urethra (the tube between the bladder and the outside of the body). In men, it usually affects the urethra. In many cases, there are no symptoms — seven in 10 women and five in 10 men will not notice that they have it.  

It’s easy to treat with antibiotics but can cause other health problems if it is not treated early on, including pelvic inflammatory disease, reactive arthritis and infertility.

How to tell if you have chlamydia

You may not have any symptoms of chlamydia — many people don’t know they have it. If you get symptoms, they will usually occur 1–3 weeks after infection, although in some cases, they may not appear for several months. Symptoms may go away after a few days but you may still have the infection and could infect others.

It’s a good idea to get tested every year if you’re sexually active and under 25, or more often if you have more than one partner.

The most common symptoms are pain in your genitals and/or pain when you urinate.

Chlamydia symptoms in men

Half of infected men will not notice any symptoms. The most common symptoms in men include:

  • A burning or itchy urethra
  • Discharge from the end of your penis — this can be white, cloudy or watery
  • Discomfort or pain when having sex
  • Pain when urinating
  • Painful or swollen testicles

If chlamydia is left untreated, it can cause your testicles and the tubes that carry sperm from your testicles to your penis (epididymis) to swell. This can cause infertility.

Chlamydia symptoms in women 

Seven in 10 infected women will not notice any symptoms. The most common symptoms in women include:

  • Abnormal bleeding from your vagina eg in between periods and/or after sex
  • Pain during sex
  • Pain in your pelvis or tummy, especially during sex
  • Pain when urinating
  • Unusual vaginal discharge

If chlamydia is left untreated, it can spread to your womb and cause pelvic inflammatory disease (PID). This is a serious condition and is a common cause of infertility and ectopic pregnancy (when a fertilised egg implants outside of your womb). 

Chlamydia symptoms in the rectum, throat and eyes

If your back passage (rectum) is infected after having unprotected anal sex, you may have anal bleeding or anal discharge

If you have unprotected oral sex, chlamydia can infect your throat. However, this is uncommon and usually does not cause symptoms.

Chlamydia can also affect your eyes or nose. If your eyes come into contact with infected semen or vaginal fluid, your eyes may become red and/or painful. You may also have discharge from your eyes (conjunctivitis).

If you have any chlamydia symptoms, or if your partner has been diagnosed with chlamydia, you should ask your GP for advice as soon as possible or visit a sexual health clinic. 

If you don't have any symptoms but are concerned that you have chlamydia, you can still get tested. If you are aged under 25 and are sexually active, you should get tested for STIs every year or every time you have a new sexual partner.

Talk to your doctor if you’re concerned about symptoms

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Diagnosis and tests for chlamydia

Getting a chlamydia test is easy and is the only way to find out if you have chlamydia — you can get the test whether or not you have symptoms. It’s a good idea to get tested regularly, especially if you have more than one sexual partner, sometimes have unprotected sex, or if you’re planning to become pregnant.

If you are aged under 25, live in England and are sexually active, it is recommended that you get tested for STIs every year or every time you have a new sexual partner. 

When should I get tested?

Getting tested as soon as possible will reduce the risk of complications caused by chlamydia. You can have a test at any time. Your nurse or doctor may recommend getting another test if your first test is performed less than two weeks after having sex. This is because the test does not always detect chlamydia in the early stages. 

You should get tested if:

  • A condom split when you were having sex
  • A sexual partner tells you they have an STI
  • You are concerned that you have an STI
  • You are pregnant or trying to get pregnant
  • You have had unprotected sex with a new partner, or you or your partner have had unprotected sex with other people
  • You or your partner has any chlamydia symptoms

What does the chlamydia test involve?

If you visit a sexual health clinic or your GP refers you to one, they may test for more than one type of STI. 

The test is simple, painless and usually reliable. You may not need to be examined by a doctor or nurse as you may be able to collect the sample of cells for testing yourself. These cells are sent to a lab for testing. The cells can either come from a urine sample or a swab of the discharge from the infected area eg the anus or vagina.

The swab test

A sample of the discharge from inside your vagina or anus is collected using a small cotton bud. It can be done by a doctor or nurse or you may be given a kit so you can do this yourself at home. 

In women, the swab is inserted about 5cm into the vagina and rotated for a few seconds — this is the most accurate way to test for chlamydia. If performed by a nurse or doctor, a second swab may be taken to collect cells and mucus from the cervix.

In men, a swab can be taken from the urethra. 

If you have had anal or oral sex, a swab may be taken from your rectum or throat. 

The urine test

A urine sample is collected by urinating into a small container. Ideally, this should be done at least one to two hours after you last urinated.

In most cases, men are tested using a urine sample and women are tested using a swab of the discharge or a urine sample. 

You can usually get your results after seven to 10 days. If it is very likely that you have chlamydia, you may be given treatment before you get your test result. 

If the test is negative, you might have another test about a fortnight later because the infection can be difficult to detect during the first two weeks. You may be offered a repeat test after three to six months if you needed treatment, to check you haven’t been reinfected. Young adults who have tested positive for chlamydia have a higher risk of reinfection.

Causes of chlamydia

Chlamydia is caused by bacteria called chlamydia trachomatis. You’re most at risk if:

  • You have unprotected sex with someone who already has the infection
  • You’ve been infected with another STI such as HIV or gonorrhoea
  • You’ve had more than one sexual partner during the past year

Infection occurs when you come into contact with infected semen or vaginal fluid. You can’t catch chlamydia from hugging, kissing or sharing cups or cutlery. 

Common treatments for chlamydia

The usual treatment is antibiotics for up to 10 days. This treatment is successful in 95% of cases if the antibiotics are taken exactly as instructed. Your doctor may start you on antibiotics before your diagnosis is confirmed with a chlamydia test if it is very likely that you have this infection. If not, you will be treated with antibiotics after getting a positive test result. 

The two most common antibiotics prescribed to treat chlamydia are: 

  • Azithromycin — taken orally as two or four tablets in one go
  • Doxycycline — taken orally as two capsules per day for a week

If you are allergic to these antibiotics or are pregnant, you may be prescribed different antibiotics eg amoxicillin or erythromycin. If your doctor is concerned about complications from chlamydia, they may prescribe a longer course of antibiotics. Side effects are usually mild and include: 

  • Diarrhoea
  • Feeling nauseous
  • Tummy pain
  • Vaginal thrush in women

You and your partner should avoid having sex, even if you use a condom until you have completed your antibiotic treatment — this includes anal, oral and vaginal sex. If you are treated with a one-day course of azithromycin, you should avoid sex for a week after treatment to ensure you do not pass on the infection or immediately catch it again.

Will I need to go back to the sexual health clinic?

If you take your antibiotics as prescribed, you may not need to go back to the sexual health clinic. However, your doctor may recommend you go back to be tested again if: 

  • You are pregnant
  • You did not take your antibiotics correctly or missed a dose
  • You had sex before you or your partner completed treatment
  • Your symptoms continue

If you are aged under 25, you will be asked to return for another test three months after completing your treatment as young adults are at higher risk of reinfection. 

Testing and treating sexual partners

If you test positive for chlamydia, it is important to let your current or recent sexual partner(s) know so that they can be tested and treated too — this will help prevent the infection from being passed on.

All sexual partners from six months before your positive test should be tested. If your current sexual partner tests positive but does not get treatment, you can be reinfected after your treatment has completed.

A sexual health adviser can help you contact your sexual partners or contact them for you without revealing your identity.

Why should I have treatment if I have no symptoms?

If you test positive for chlamydia but do not have any symptoms, you should still get treatment as your infection can still spread and cause serious complications months or years later. You can also still infect your sexual partners. 

Chlamydia complications

Chlamydia complications in men

  • Inflammation of the testicles and epididymis (epididymitis or epididymo-orchitis) — this can cause swelling and pain; it is usually treated with antibiotics and if left untreated can cause infertility
  • Reactive arthritis — chlamydia is the most common cause of sexually acquired reactive arthritis (SARA), which causes inflammation of your joints, eyes and/or urethra a few weeks after infection with chlamydia; there is no cure but it usually gets better on its own after a few months; it can affect women but usually affects men

Chlamydia complications in women

Chlamydia can spread to your womb, ovaries and/or fallopian tubes and cause pelvic inflammatory disease (PID) — 10-40% of women with chlamydia develop PID. PID can develop suddenly, causing pain and fever, or develop gradually over months or years without any symptoms (silent PID). 

Symptoms of PID are similar to chlamydia and include: 

  • Bleeding in between periods and after sex
  • Discomfort or pain during sex
  • Pain when urinating

PID can cause:

  • Chronic (long-term) pelvic pain
  • Increased risk of ectopic pregnancy
  • Infertility or difficulty getting pregnant 

PID is usually treated with a two-week course of antibiotics. Early treatment reduces the risk of complications, such as infertility

If you are pregnant and your chlamydia is left untreated, it can increase the risk of premature birth (before 37 weeks) and low birthweight. Untreated chlamydia can also infect your baby. If your baby is infected, they may develop an eye infection (conjunctivitis) and/or lung infection (pneumonia). If your baby has symptoms of these conditions, your midwife or GP can arrange a chlamydia test for them and they can be treated with antibiotics. 

Frequently asked questions

How long can you have chlamydia without knowing?

You can have chlamydia for months or years without knowing as it does not always cause symptoms. Around seven in 10 women with chlamydia do not notice symptoms.

How serious is chlamydia?

Although chlamydia often causes no or mild symptoms, if it is left untreated, it can lead to serious complications, such as infertility.

Can chlamydia go away on its own?

Chlamydia does not usually go away on its own. Your symptoms may go away but if you have not had treatment, you will still carry the infection and can pass it onto your sexual partner. 

Does chlamydia mean your partner cheated?

Chlamydia can stay in your body for months or years without causing any symptoms. During this time, you can still pass on the infection. If your partner has chlamydia, it doesn’t therefore necessarily mean that they have had sex with someone else recently. 

Does chlamydia have a smell?

Chlamydia can sometimes cause discharge from the affected area eg the anus, vagina or end of the penis. This discharge can have a strong smell. 

How do I know my chlamydia is gone?

Antibiotic treatment is usually successful in treating chlamydia if taken correctly. However, the only way to know for certain is to have a chlamydia test.

If I had chlamydia for two years, can I still get pregnant?

In most cases, having had chlamydia doesn’t affect a woman's ability to get pregnant. However, if you have had repeated bouts of chlamydia or your chlamydia wasn’t treated and you developed pelvic inflammatory disease (PID), it may be harder to get pregnant.

How do you get chlamydia without being sexually active?

You can get chlamydia without having sexual intercourse or penetration if you share sex toys, come into close contact with the genitals of an infected person or touch infected vaginal fluid or semen and then touch your eyes.

How easy is it to get chlamydia?

Chlamydia is usually spread through anal and vaginal sex, and to a lesser extent, oral sex. You can also get chlamydia if you share sex toys or touch infected vaginal fluid or semen. You can’t get chlamydia from kissing, hugging or sharing cups and cutlery.

How long does it take for chlamydia to show up positive on a test?

Once you have a chlamydia test, you will usually need to wait seven to 10 days for your results.

How long is chlamydia contagious?

Chlamydia remains contagious for as long as it is in your body. If left untreated, it can remain in your body for years.

Does chlamydia cause itching?

Yes, chlamydia can cause itching, similar to other sexually transmitted infections (STIs) such as genital herpes and gonorrhoea.

Can you catch chlamydia from a toilet seat?

No, you can’t catch chlamydia from a toilet seat or from sharing cups, cutlery, baths or towels.