What is chlamydia?

Chlamydia is a sexually-transmitted infection (STI) caused by a bacteria called Chlamydia trachomatis. It is one of the most commonly reported STIs in the US and can be spread by having vaginal, oral or anal sex.

Chlamydia can affect both men and women. It is most common in young sexually-active adults, although it is becoming increasingly common in older adults. Most people that are infected with chlamydia will not have any symptoms, while others can experience pain when urinating or having sex and/or have an abnormal discharge from the penis or vagina.

Sexually-transmitted infection

A viral or bacterial infection contracted through sexual intercourse or genital contact. Such an infection can lead to development of diseases such as chlamydia, gonorrhea, genital herpes and AIDS.


Chlamydia is caused by a bacterium called Chlamydia trachomatis. It is a STI, which means that you can get it by having unprotected sex. If you are a pregnant woman with chlamydia, you can also pass the infection on to your baby during childbirth.

Chlamydia can be contracted by having unprotected sex. 

Risk factors

Anyone who is sexually active can get chlamydia, but there are some people who have a higher risk of getting the infection. You are more likely to get chlamydia if you:

  • Do not practice safe sex;
  • Have multiple sexual partners;
  • Are a young adult, and;
  • Have a past history of a STI.

Signs and symptoms

If you are infected with chlamydia, you may not have any symptoms at all. If you do get symptoms, they can be slightly different in men and women.

Men infected with chlamydia may experience:

  • Pain or discomfort when urinating;
  • A discharge from the penis, and;
  • Swollen and sore testicles.

Women may experience:

  • An unusual discharge from the vagina;
  • Pain or a burning feeling when urinating;
  • Pain during sex;
  • Bleeding after sex;
  • Bleeding between periods, and;
  • Pain in the lower abdomen and fever.

Methods for diagnosis

To work out if you have chlamydia, a doctor will most likely collect a sample of your urine, or take a swab from the vagina, cervix, penis or anus. The samples are sent off to a laboratory and tested to see if the bacteria that cause chlamydia are present.


The lower part of the uterus, leading out into the vagina.

Types of treatment

If you have chlamydia, your doctor may prescribe antibiotics, such as azithromycin or doxycycline, to treat the infection. A second test one or two months after treatment is usually recommended, to check that it is completely gone.

If you have chlamydia, it is possible that your sexual partner may also have it and could potentially pass it on to you again after you have finished treatment. It is recommended that your sexual partner is also tested and treated for chlamydia, if present, to reduce their risk of developing complications.

Potential complications

If a chlamydia infection is not treated, it can lead to some other serious health problems, including:

Pelvic inflammatory disease

Pelvic inflammatory disease can develop in women with chlamydia. The condition occurs when the infection affects parts of the female reproductive system, which includes the uterus and fallopian tubes. This may result in fever and pain in the pelvic region. In severe cases, this can cause permanent damage and may lead to difficulty getting pregnant, or an inability to get pregnant (infertility). The more often you get chlamydia, the more likely that your fertility could be affected.

Infections in newborns

If a pregnant woman has chlamydia, the infection can be passed on to her baby during childbirth. This can cause the baby to develop an eye infection (conjunctivitis) or a lung infection (pneumonia).


In men, a chlamydia infection can cause inflammation of the epididymis, which is the tube located next to each testicle. This condition is known as epididymitis and can cause swelling and pain in the scrotum.

Prostate gland infection

In men, a chlamydia infection can also spread to the prostate gland, which is part of the male reproductive system. The infection can cause a fever and chills, pain when urinating, or pain during and after sex.

Reactive arthritis

If you have chlamydia, you may have an increased chance of developing a condition called reactive arthritis, which is also sometimes known as Reiter's syndrome. Symptoms include pain and swelling in the joints. This condition usually gets better with time and is unlikely to cause any permanent joint damage.


A connecting surface or tissue between two bones.

Reiter's syndrome

An autoimmune condition marked by painful and swollen joints, pain during urination and eye redness.


Most cases of chlamydia can be successfully treated with antibiotics.


Chlamydia can be prevented by practicing safe sex, which means using a barrier, such as a condom, when having sex. Because some people who are infected with chlamydia do not show any symptoms, getting tested regularly if you have a high risk of getting the infection may help prevent spreading it to others. To prevent chlamydia being passed on to babies during childbirth, doctors usually recommended that pregnant women get tested for chlamydia.

Chlamydia can be prevented by using condoms during sex. 

FAQ Frequently asked questions