Image: Breslavtsev Oleg/

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 the most common sexually transmitted infection 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 and bisexual men. If left untreated, the infection can cause complications, including infertility and reduced fertility. It can increase the likelihood of passing on or acquiring HIV.


Chlamydia is caused by bacteria called Chlamydia trachomatis. It can be transmitted via infected semen, pre-cum, or vaginal fluids during anal, oral and vaginal sex, if you do not use a condom. 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.

Chlamydia can also be passed on to a child during childbirth and can affect the baby’s eyes and cause pneumonia. During pregnancy, all people with HIV should have a sexual health check-up.


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 condomless sex with new or casual partners. Gay and bisexual men who are having sex without a condom – including oral sex – with new or casual partners are advised to have a sexual health check every three months.

Most HIV treatment centres in the UK 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. Over three-quarters of people have no symptoms after infection with chlamydia.

Chlamydia symptoms may include milky discharge from the genitals and pain when urinating. It is more common to have discharge from the penis than the vagina. Less common symptoms include pain or swelling in the testicles.

"A general sexual health check-up at a genitourinary medicine (GUM) or sexual health clinic will include a test for chlamydia."

Lower back pain and abdominal pain can be a symptom, as well as vaginal bleeding during sex, bleeding between periods and heavier bleeding during a period. 

If you have been infected anally, there may be soreness around the anus and a discharge. Infection in the eyes causes conjunctivitis – inflammation, discharge and pain. Infection in the throat is uncommon and usually without symptoms.

Untreated chlamydia in the vagina can lead to pelvic inflammatory disease (PID), an infection of the upper part of the female reproductive system, which can cause long-term pelvic pain, infertility, and ectopic pregnancy (pregnancy outside the womb). Untreated chlamydia can also cause testicular problems and cause reduced fertility or infertility.

Untreated chlamydia during pregnancy can increase the risk of miscarriage or premature birth.

Untreated chlamydia may lead to sexually acquired reactive arthritis (SARA), leading to pain in the joints, eyes or urethra (the tube urine passes out of the body through). Anyone can get SARA, but research shows its more common in women. 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 a common sexually transmitted infection, caused by bacteria called Chlamydia trachomatis. Women can get chlamydia in the cervix, rectum, or throat. Men can get chlamydia in the urethra (inside the penis), rectum, or throat. Chlamydia is treated with antibiotics.


Any perceptible, subjective change in the body or its functions that signals the presence of a disease or condition, as reported by the patient.



How well something works (in real life conditions). See also 'efficacy'.

sexually transmitted infections (STIs)

Although HIV can be sexually transmitted, the term is most often used to refer to chlamydia, gonorrhoea, syphilis, herpes, scabies, trichomonas vaginalis, etc.


Refers to the mouth, for example a medicine taken by mouth.

Chlamydia is usually diagnosed by checking a urine sample. 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.

Sometimes, you may be given swabs to take your own sample from the throat or anus, either in the clinic or by having the swabs mailed to you at home. These self-samples are just as accurate as testing performed by a healthcare worker. 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. 

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. In the UK, this consists of a seven-day course of doxycycline. In other parts of the world, you may be given 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 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. But, if you are under age 25, it is recommended to get tested again three months after being treated for chlamydia.

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. If you would like help notifying your partner that they may have been exposed to chlamydia, your clinic can contact your partner for you without mentioning your name.

Next review date