About chlamydia

Chlamydia is the most common sexually transmitted infection (STI) in the UK. It particularly affects men and women under the age of 25.

Chlamydia can be treated with antibiotics but, if left untreated, it can lead to serious health problems, including infertility.

Symptoms of chlamydia

Around half of men and seven in 10 women with chlamydia don't have any symptoms. You can still pass on the infection to a sexual partner even if you don’t have any symptoms. If you have symptoms, these usually begin between one and three weeks after being infected. 

In women, symptoms to look out for are:

  • increased or unusual discharge from the vagina – such as a change in colour, texture or smell
  • bleeding from the vagina after sex or between periods
  • pain in the lower abdomen (tummy) or pelvis
  • pain when passing urine
  • pain during sex

In men, symptoms to look out for are:

  • a milky discharge from the penis
  • pain when passing urine
  • pain and swelling in the testicles

You can get a chlamydia infection in your rectum (back passage) if you have anal sex, which may cause a discharge or bleeding from your anus, and you may feel some discomfort. However, often there are no symptoms.

If infected semen or vaginal fluid comes into contact with your eyes, you can get an infection of your conjunctiva (the transparent surface layer that covers the white of the eye).

If you have any of these symptoms, see your GP or go to a sexual health clinic.

Complications of chlamydia

If you’re treated early for chlamydia infection, you’re less likely to go on to have long-term health problems as a result. Not everyone who has chlamydia has complications but without proper treatment the infection can spread to other parts of your body.

If you’re a woman, chlamydia can spread to your womb (uterus), ovaries and fallopian tubes causing pelvic inflammatory disease. This happens in up to four out of 10 women with chlamydia. If you have pelvic inflammatory disease, you may a symptom of long-term pelvic pain. Pelvic inflammatory disease can lead to complications including blocked fallopian tubes, infertility and ectopic pregnancy. This is when a pregnancy occurs outside the womb, usually in a fallopian tube. Chlamydia can also spread to your liver causing pain and inflammation. This usually gets better with the correct antibiotic treatment.

If you’re a man, chlamydia can lead to an infection in your testicles that could possibly reduce your fertility.

Rarely, chlamydia can lead to inflammation of the joints in both men and women. This is known as reactive arthritis.

Causes of chlamydia

Chlamydia is caused by C. trachomatis bacteria, which are found in the semen of men and vaginal fluids of women who have the infection. The bacteria can survive in the cells of the cervix (neck of the womb), the urethra (the tube that carries urine from the bladder and out through the penis or vulva), the rectum (back passage) and sometimes in your throat and eyes.

Chlamydia is passed from one person to another through unprotected vaginal, anal or oral sex. It can also be passed on by sharing sex toys if you don’t wash them or cover them with a new condom each time they’re used.

Chlamydia can be passed from a pregnant woman to her baby during a vaginal birth.

You can’t get chlamydia from kissing, hugging, sharing baths or towels, swimming pools, toilet seats or from sharing cups, plates or cutlery.

Diagnosis of chlamydia

If you think you may have chlamydia, see your GP or go to a sexual health clinic where you will see a doctor for your tests. You can have a test for chlamydia even if you don't have any symptoms.

You don't have to ask your GP to refer you to a sexual health clinic; you can make your own appointment. All visits are confidential and you don't have to give your real name. Details won't be sent to your GP without your consent.

Chlamydia tests are available at youth clubs and universities. There are some services that you can use by collecting a sample at home and sending it away for testing. You can buy test kits from some pharmacies, but the accuracy of these tests varies. Speak to your pharmacist for advice.

There are different ways to test for chlamydia.

  • You may be asked to provide a sample of urine – you may be instructed to not pass urine for up to two hours before this test.
  • Your doctor or nurse may use a swab (similar to a small round cotton bud) to take a sample of the cells from your vagina (for women) or from the tip of your penis (for men). If you're female, you may have the option to collect a sample of cells from your vagina yourself using a swab or a tampon.
  • If you have had anal or oral sex, your doctor or nurse may use a swab to take a sample from your rectum or throat.

The samples will be sent to a laboratory for testing, but if you have symptoms of an STI, your doctor at the clinic may look at your samples under a microscope straightaway. If he or she can see a high number of pus cells (white blood cells), this may indicate a chlamydia infection. Your doctor at the clinic will give you this result immediately along with the treatment for chlamydia and then send the sample to a laboratory to confirm the diagnosis.

If the tests show that you have chlamydia, it's important to contact your previous sexual partners who may be at risk, to prevent them from spreading the infection to others. Clinics can send anonymous letters on your behalf if you're willing to provide details.

Treatment of chlamydia

You will be prescribed an antibiotic to treat chlamydia. This often comes as a single dose. You will take this at the clinic or at your GP surgery. However, if for some reason you can’t take this (for example, you’re allergic to it) you will be prescribed an alternative course of antibiotics that you may need to take for up to two weeks.

You will be asked not to have sex again for seven days if you were given the single dose, or until you have finished all the antibiotics if you were taking a longer course.

Your previous sexual partners should be treated for chlamydia too. If they have symptoms, they may be treated for chlamydia before the results of their laboratory tests come back. Treating chlamydia early can help to prevent further complications and you passing it on to anyone else.

The antibiotics that are used to treat chlamydia can interfere with the contraceptive pill, the contraceptive vaginal ring and the contraceptive patch. If you’re using any of these methods of contraception, you may need to use an alternative method, such as condoms. Talk to your doctor or nurse about how the antibiotics may affect your contraception.

Special considerations

If you're pregnant or breastfeeding

If you have chlamydia when you're pregnant, there is some limited evidence to show that chlamydia may lead to complications such as miscarriage or having your baby prematurely. You can take certain antibiotics while you’re pregnant to treat the infection.

If you have untreated chlamydia during the birth of your baby, he or she may develop a chlamydial infection soon after birth. This can affect your baby’s eyes (conjunctivitis) or lungs (pneumonia). Your baby can be treated with antibiotics for both of these conditions.

Tell your doctor or nurse if you’re pregnant, or think you might be, or if you’re breastfeeding. This will affect the type of antibiotic that you’re given.

Prevention of chlamydia

There are ways to lower your risk of getting or passing on chlamydia.

  • Use condoms when having vaginal, oral or anal sex.
  • Try not to share sex toys with different partners. If you do share them, wash them or cover them with a new condom before anyone else uses them.
  • Before having sex with a new partner, you could both consider having a test for chlamydia and other STIs.

How soon after having unprotected sex can I have a test for chlamydia?


You can be tested straight away if you’re worried that you may have become infected with chlamydia. You may be asked to return two weeks later for a second test to be sure the results are correct. 


Chlamydia often has no symptoms, so you can make an appointment to be tested with your GP or a sexual health clinic if you’re concerned that unprotected sex might have led to an infection, even if you have no symptoms. You might be asked to come back after two weeks to confirm your diagnosis. If you’re diagnosed with chlamydia, don’t have sexual contact again until after you have finished the course of treatment. To reduce your risk of getting infected again, always use condoms every time you have sex, oral sex or if you share sex toys.

Can chlamydia go away without treatment?


Chlamydia infection can clear up on its own, but this is unlikely. Even without symptoms you could still have the infection. If you delay seeking treatment, you risk the infection causing long-term damage and you may still be able to pass the infection on to someone else. 


In women, even if there are no symptoms, the infection can affect the fallopian tubes, ovaries and womb (uterus), causing damage to them, possibly leading to infertility. Other complications of leaving chlamydia untreated include pelvic inflammatory disease in women. This can cause complications such as long-term pelvic pain, blocked fallopian tubes and ectopic pregnancy. This is when a pregnancy occurs outside the womb, usually in a fallopian tube.

In men, the infection can affect the testicles and may lead to infertility, if left untreated.

Untreated chlamydia can also cause inflammation in the joints, known as reactive arthritis, in both men and women.

It’s important to see your GP or visit a sexual health clinic if you think you may have chlamydia.

Do I need to have a test again when I have finished the treatment to check that chlamydia has cleared up?


You won't usually need to have another chlamydia test after you have finished your treatment. 


A follow-up test to check the infection has cleared up isn't usually needed if you take the treatment correctly and you don't have sex again until you (and your partner if necessary) have completed the course of antibiotics.

However, get tested for chlamydia again if you:

  • and your partner have had unprotected sex before both of you have completed your treatment
  • have had unprotected sex with a new sexual partner
  • still have symptoms, or you develop new symptoms of chlamydia
  • are pregnant

Is it possible to tell how long I have had the infection?


It can be difficult to know how long you have had chlamydia for, particularly if you haven't had any symptoms.


As you may not have symptoms with a chlamydia infection, it's possible to have it for months or even years without knowing. This can make it difficult to determine how long you have had it, particularly if you have had a number of sexual partners.