Factsheet Chlamydia

Selina Corkery, Published June 2017

Key points

  • Chlamydia can be transmitted via infected semen or vaginal fluids.
  • Using a condom during sex is an effective way of preventing  chlamydia.
  • Chlamydia is easily treated with a single dose or course of antibiotics.

Chlamydia is a sexually transmitted infection. It is one of the most common sexually transmitted infections in the UK, but it can be easily treated and cured.

Anyone who is sexually active can get chlamydia, but the infection is more common in some groups, including young people and gay men. If left untreated, the infection can cause complications, including infertility in women and reduced fertility in men. It can increase the likelihood of passing on HIV.


Chlamydia is caused by bacteria called Chlamydia trachomatis. It can be transmitted via infected semen or vaginal fluids during anal, oral and vaginal sex, if you do not use a condom (unprotected sex). It can also be passed on by sharing sex toys if they are not washed or not covered by a new condom each time they are used. You can get chlamydia if your genitals come in contact with the genitals of someone who has chlamydia, or if you get infected semen or vaginal fluid in your eye. However, you do not get chlamydia from contact such as kissing or hugging, or from sharing towels or cutlery.

In a person with HIV who is not taking HIV treatment, untreated chlamydia may make them more infectious. This is because untreated sexually transmitted infections can increase HIV viral load in genital fluids. However, if the person with HIV is taking effective HIV treatment and has an undetectable viral load, they will not pass HIV on. Chlamydia will not make a difference to this.

In an HIV-negative person, having chlamydia can make it more likely that they will be infected with HIV if they are exposed to the virus.

"A general sexual health check-up at a sexual health clinic will include a test for chlamydia."

Chlamydia can also be passed on from mother to child during childbirth and can affect the baby’s eyes and cause pneumonia. All women with HIV should have a sexual health check-up during their pregnancy.


Using a condom for anal or vaginal sex, or a condom or dental dam (a sheet of latex) for oral sex, is an effective way of avoiding transmission of chlamydia.

Also, don’t share sex toys. If you do, wash them or cover them with a new condom before anyone else uses them.   

If you are sexually active, you are advised to have regular sexual health check-ups, especially if you have recently had a new partner. It is recommended that people with HIV have a sexual health check at least once a year. There you will be tested for chlamydia and other sexually transmitted infections. In some situations, having a check-up more often may be recommended, such as if you are having unprotected sex with new or casual partners. Gay men having unprotected sex – including oral sex – with new or casual partners are advised to have a sexual health check every three months.

Most HIV treatment centres have an associated sexual health clinic, where confidential and free treatment can be obtained without referral from your GP or HIV doctor.


Chlamydia can affect the anus, penis, cervix, throat and eyes. 

Symptoms of chlamydia normally occur one to three weeks after infection. However, many people who have chlamydia are unaware that they have the infection. It is thought that around 75% of women and 50% of men have no symptoms after infection with chlamydia.

When symptoms do occur, in men it usually consists of a milky discharge from the penis, particularly in the morning, and pain when urinating. Chlamydia can also cause the testicles to swell. If a person has been infected anally, there may be soreness around the anus and a discharge.

Women with chlamydia may notice a milky discharge from the vagina and/or lower abdominal or back pain, or pain when having sex or urinating. There may also be vaginal bleeding during sex, bleeding between periods and heavier bleeding during a period. 

Infection in the eyes causes conjunctivitis – inflammation, discharge and pain. Infection in the throat is uncommon and usually without symptoms.

If chlamydia is left untreated it can lead to pelvic inflammatory disease (PID) in women, which can cause long-term pelvic pain, blocked fallopian tubes and infertility, and ectopic pregnancy (pregnancy outside the womb). 

Men are less likely to develop serious complications, though untreated chlamydia may cause infertility.

Men and, more rarely, women may develop sexually acquired reactive arthritis (SARA), leading to pain in the joints, eyes or urethra (the tube urine passes out of the body through). Most people recover from this in a few months, and painkillers can help treat symptoms.


A general sexual health check-up at a genitourinary medicine (GUM) or sexual health clinic will include a test for chlamydia. It is important to get tested as soon as possible if you think you are at risk of infection with chlamydia. You can have a test even if you have no symptoms. You may be advised to have a second test a couple of weeks later as well.

Chlamydia is usually diagnosed by checking a urine sample, particularly for men. Sometimes, swabs may be taken to see if the infection is present in the urethra, vagina or cervix. If you have had anal or oral sex, you may have swabs taken of your throat or anus. You can buy kits to test yourself at home, but these are not always very accurate. 

It can take at least a week for tests to show if chlamydia is present. It is important to contact your clinic for the result of your test, so that you can be given treatment if the infection has been detected. If you are under 25 years of age, you can get tested as part of the National Chlamydia Screening Programme (NCSP).

Chlamydia is often the cause of non-specific urethritis (NSU), the symptoms of which are very similar, and which is diagnosed and treated in the same way.


Chlamydia is treated with antibiotics, which are very effective in treating it. Normally this consists of a seven-day course of doxycycline, or a single dose of azithromycin, given as two or four tablets. It is important to take all your tablets to ensure that the infection is completely cleared from your body. You may still have symptoms for a few days after taking azithromycin as the antibiotic takes time to work.

Tell the treating doctor if you are pregnant, as this will affect the antibiotic you are given. 

To prevent reinfection, you should not have unprotected sex (sex without a condom) until a week after your treatment is finished.

You may have to abstain for longer if your partner has not yet been tested or treated, or if you still have symptoms. If you follow this guidance, you won’t normally need to go back to the clinic for another test unless you think you may have been exposed to chlamydia again, or you are pregnant. 

It is possible to become infected with chlamydia again after being successfully treated. To avoid this, make sure any of your sexual partners have also been treated. Condoms, used properly and consistently, can prevent infection with chlamydia and many other sexually transmitted infections.

This factsheet is due for review in June 2020

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This content was checked for accuracy at the time it was written. It may have been superseded by more recent developments. NAM recommends checking whether this is the most current information when making decisions that may affect your health.
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This content was checked for accuracy at the time it was written. It may have been superseded by more recent developments. NAM recommends checking whether this is the most current information when making decisions that may affect your health.

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