Chlamydia

Overview

Chlamydia is a bacterial infection that is usually spread through sex. The NHS says most people have no symptoms and may not know they have it. When symptoms do occur they can include unusual discharge, pain when passing urine, and pelvic or testicular pain. It can be treated with antibiotics, and WHO describes it as curable. Untreated infection can cause pelvic inflammatory disease and can affect fertility. Testing uses a urine sample or a swab.

Symptoms

What a clinician may find

• Unusual vaginal discharge or discharge from the penis.
• Bleeding after sex or between periods.
• Pain or swelling in the testicles.
• Discomfort or discharge from the rectum.

Complications

• Pelvic inflammatory disease in women, when the infection spreads to the womb, ovaries or fallopian tubes.
• Difficulty getting pregnant or infertility, long-lasting pelvic pain and a higher risk of ectopic pregnancy after pelvic inflammatory disease.
• Pain and swelling of the epididymis in men, which the NHS describes as very rare.
• A possible increase in the risk of premature birth or low birthweight when infection is untreated in pregnancy.
• Eye infection or pneumonia in a newborn who caught the infection during birth.

Diagnosis

Chlamydia is diagnosed by testing a urine sample or a swab. The test most often used is a nucleic acid amplification test, known as a NAAT, which WHO describes as the gold standard. Some areas offer postal home testing kits. Sexual health services advise that testing too soon after possible exposure can miss an infection. In England the national screening programme recommends that sexually active women under 25 are tested each year and after each new partner.

Treatment

The NHS says chlamydia can usually be treated effectively with antibiotics, and WHO describes it as curable. The usual antibiotic options are doxycycline and azithromycin tablets. The 2026 BASHH guideline recommends doxycycline as the first-line treatment. Current and recent partners are also tested and treated. The NHS advises avoiding sex until treatment is completed by the person and their partners. Under-25s who have chlamydia are offered another test 3 to 6 months after treatment, to look for reinfection.

Prevention

WHO says correct and consistent use of condoms during sex is the most effective way to prevent chlamydia. The CDC, a US source, says condoms and dental dams protect against chlamydia when used correctly every time, including for oral sex. The NHS says sex toys can pass the infection on unless they are washed or covered with a new condom each time. There is no vaccine against chlamydia.

Key facts

What are the symptoms of chlamydia?

Most people with chlamydia do not notice any symptoms, according to the NHS, so many do not know they have it. When symptoms do occur, the NHS says they usually appear between 1 and 3 weeks after sex with someone who has chlamydia, though for some people they do not develop until many months later. Symptoms can fade after a few days, but the infection can still be present and can still be passed on.

In women, the NHS lists vaginal discharge that is not normal for the person, bleeding after sex or between periods, a burning feeling when passing urine, and pain in the lower tummy. In men, it lists white, cloudy or watery discharge from the tip of the penis, burning and itching around the penis and testicles, pain and swelling in the testicles, and a burning feeling when passing urine.

Infection of the rectum, which can follow anal sex, can cause discomfort and discharge from the back passage. The CDC notes that chlamydia often causes no symptoms yet can still cause serious harm.

How is chlamydia passed on?

Chlamydia is caused by the bacterium Chlamydia trachomatis. The NHS says it is usually spread through vaginal, oral or anal sex without a condom, and through contact with semen or vaginal fluid, including on sex toys or hands. Sex toys can pass it on if they are not washed or covered with a new condom each time they are used. The infection can also pass from a pregnant person to the baby during birth.

The NHS says chlamydia is not spread by kissing or hugging, swimming pools, toilet seats, sharing baths or towels, or sharing cups, plates or cutlery.

The NHS lists a new sexual partner, sex without a condom and a partner's diagnosis of a sexually transmitted infection among the situations in which a test is advised.

How is chlamydia diagnosed?

The NHS says the only way to know whether someone has chlamydia is to be tested, and a test can be done whether or not there are symptoms. Testing uses a urine sample or a swab. The NHS says men are usually asked for a urine sample, while women usually take a swab from inside the vagina. Sexual health services advise that testing too soon after possible exposure can miss an infection.

The test most often used is a nucleic acid amplification test, known as a NAAT, which WHO describes as the gold standard for diagnosing the infection. Some areas offer postal home testing kits, particularly for people under 25.

The National Chlamydia Screening Programme in England aims to reduce the harm caused by untreated infection. It recommends that sexually active women under 25 are tested each year and after each new partner.

How is chlamydia treated?

The NHS says chlamydia can usually be treated effectively with antibiotics, and WHO describes it as curable. The usual antibiotic tablets are doxycycline and azithromycin. The 2026 guideline from the British Association for Sexual Health and HIV (BASHH) recommends doxycycline as the first-line treatment.

The NHS says current and recent sexual partners should be tested and treated, and that sexual health clinics can help people contact their partners. It advises avoiding sex until the person and their partners have completed treatment, and, after azithromycin, waiting 7 days before sex.

The NHS says under-25s who have chlamydia are offered another test 3 to 6 months after treatment, to look for reinfection. A GP or sexual health clinic can give advice on treatment and follow-up.

What problems can untreated chlamydia cause?

WHO says long-term problems are unlikely if chlamydia is treated early, and that untreated infection can lead to pelvic inflammatory disease and an increased risk of infertility and ectopic pregnancy. In women the infection can spread to the womb, ovaries or fallopian tubes and cause pelvic inflammatory disease. The NHS says this can lead to difficulty getting pregnant, long-lasting pelvic pain and a higher risk of ectopic pregnancy, and that the risk of problems such as infertility is lower when it is treated early.

In men, the NHS says the infection can spread to the testicles and epididymis, causing pain and swelling, though it describes this as very rare. The NHS says untreated infection could affect fertility in men. In pregnancy, untreated chlamydia may increase the risk of premature birth or low birthweight, and the baby may develop an eye infection or pneumonia after birth.

The NHS advises an urgent GP appointment or a call to NHS 111 if pelvic inflammatory disease is suspected, and A&E or a call to 999 for severe or worsening pelvic pain.

How can chlamydia be prevented?

WHO says correct and consistent use of condoms during sex is the most effective way to prevent chlamydia. The CDC, a US source, says condoms and dental dams protect against chlamydia when used correctly every time, including for oral sex. The NHS says sex toys can pass the infection on unless they are washed or covered with a new condom each time. There is no vaccine against chlamydia, according to WHO.

Because many infections cause no symptoms, testing is how they are found. A sexual health service can arrange testing whether or not there are symptoms. The English screening programme also aims to reduce harm from untreated infection through partner notification and retesting. WHO has a global strategy that aims to reduce new chlamydia cases by 2030.

Frequently asked questions