Chlamydia: Causes, Symptoms and Treatment

Although chlamydia mainly affects young women, it can occur in women and men of any age and can be passed on to anyone through sexual contact. The problem: although the infection is easy to treat, it often goes undetected because there are no symptoms – and left untreated, it can lead to more serious health problems.

That's why today you'll learn everything you need to know about chlamydia: what it is, how it's transmitted, how it's treated and how to prevent one of the most common sexually transmitted infections.

What is chlamydia?

Chlamydia is a sexually transmitted infection caused by the bacterium 'Chlamydia trachomatis'. It often goes unnoticed because symptoms either fail to appear or only show up very late.

In women, chlamydia first affects the cervix (which can lead to signs of cervicitis) and can then spread to the rest of the genital tract, including the uterus and fallopian tubes. It may also affect:

• the urethra, with symptoms such as frequent urges to urinate or pain or burning when passing urine
• the rectum, either directly through unprotected anal sex or indirectly by spreading from the cervix and vagina
• the throat, directly through unprotected oral sex, although here there are usually no symptoms and no discomfort in the throat area
• the eyes, since contact with infected genital secretions frequently triggers conjunctivitis (an inflammation of the eyes that shows up as redness and itching).

Who is at increased risk of a chlamydia infection?

Chlamydia is the most common bacterial sexually transmitted infection – and not just in the UK. To give you an idea of how widespread it is, here are a few figures:

• In 2018, the number of people infected in the USA was estimated at 4 million.
• 1 in 20 sexually active young people (aged 14 to 24) is affected, and two thirds of all new infections occur in adolescents and young adults between 15 and 24.
• In 2020, around 128.5 million new infections were recorded worldwide in people aged between 15 and 40.
• In Europe, chlamydia is the most common sexually transmitted infection. It spreads so easily because most infected people have no idea they're carrying the bacterium (since there are no symptoms at all), so they don't get tested and pass the infection on.
• According to the UK Health Security Agency (UKHSA), 168,889 chlamydia diagnoses were made in England in 2024 – making it the most commonly diagnosed sexually transmitted infection.

The statistics above already hint at who is most at risk. But to make the picture completely clear, here's an overview of the most vulnerable groups:

• Sexually active people, particularly young people who have unprotected vaginal, anal or oral sex (without a condom or another barrier method)
• People who have intimate contact with an infected partner
• People with multiple sexual partners
• Women are more susceptible to a chlamydia infection than men.

Without a test, those affected don't know they have chlamydia, so they receive no treatment and end up contributing to the spread of the infection. Another factor behind its status as the 'most common bacterial sexually transmitted infection' is the sheer variety of transmission routes. Let's look at what those are.

How is a chlamydia infection transmitted and spread?

Although you can catch it in several ways, the bacterium is mainly transmitted sexually, namely through unprotected intercourse. Let's take a closer look at how the infection can spread:

Unprotected sex

This is the most common route of transmission and includes all forms of unprotected sex (oral, vaginal or anal). Ejaculation is irrelevant here, as the bacterium can be transmitted without semen too.

Vertical transmission

During birth, an infected mother can pass the infection on to her baby. The microorganisms are transmitted vertically, via the birth canal. Conjunctivitis and pneumonia can be two of the symptoms in a newborn infected with chlamydia.

Use of sex toys

Toys can also carry and transmit the bacterium. More rarely, but still possible: anyone who uses a sex toy after an infected person, or together with them, can catch chlamydia.

It's best to use only your own toys. Or – if you're not the only one using them – only with a condom (and a water-based lubricant that won't damage the condom), and clean them before and after every use.

Direct contact with the eyes

Chlamydial conjunctivitis is an inflammation of the eye caused by infection with Chlamydia trachomatis. It happens when genital secretions containing the bacterium get into the eyes – for example, if you touch your eye after touching your intimate area (when you have an existing infection) or that of an infected partner.

Risk factors

Once you know who is most at risk and how the bacterium is transmitted, the main risk factors for chlamydia are easy to work out:

• Age: young, sexually active people between 15 and 24 are statistically more susceptible to the infection.
• Sex: studies suggest that women are more susceptible to infection than men.
• The number of sexual partners: the more sexual partners, the higher the risk of transmission, because the likelihood that one of them is infected increases.
• A history of previous sexually transmitted infections: if you've had chlamydia or other sexually transmitted infections in the past, you can get it again as soon as you have unprotected sex with an infected partner. If you'd like to read more about sexually transmitted infections and how to protect yourself properly: our blog has an article dedicated entirely to STIs.
• Sex without consent: a mother can pass the bacterium on to her baby during birth; in this case, conjunctivitis, pneumonia and a genital or rectal infection lasting up to a year can occur. If, on the other hand, a girl over one year old shows signs of infection in the vaginal, rectal or urethral area, the possibility of abuse must also be considered.

What are the symptoms of a chlamydia infection?

Many infected people have no symptoms whatsoever – which is why chlamydia is often called a 'silent infection'. That's precisely why it spreads so easily: those affected have no idea they have it, continue to have unprotected intimate contact and don't seek treatment.

If symptoms do appear, it can take up to three weeks before they're noticed. They differ in women and men as follows:

Symptoms in women

The first signs are the mildest and become more intense as the infection progresses. In women, the most common symptoms are:

• Unusual vaginal discharge with a strong, unpleasant and persistent odour (by the way: did you know there are many other reasons why the colour, consistency or smell of vaginal discharge can change? We've written about this in detail in a separate article, which you can read HERE. There we explain exactly what to look out for and what each type of discharge means.)
• Pain or burning when passing urine
• Discomfort in the lower abdomen
• Bleeding outside your period or a prolonged period (we've written more about spotting between periods in THIS article, so you know when there's cause for concern).

If the infection goes untreated and worsens, further symptoms can appear:

• Abdominal pain
• Pain during sex (chlamydia isn't the only cause of pain during or after sex, though. If you have no other signs of infection, there could be many other reasons behind it. Painful sex is never normal, however – which is why you should know exactly what's causing it and talk to your doctor about it. You can find out more in our article on dyspareunia and the causes of pain during sex.)
• Bleeding after sex
• Migraine
• Fever

And if the infection affects the anal area, the following symptoms may occur:

• Pain
• Discharge
• Bleeding

Symptoms in men 

In men, the most common symptoms of a chlamydia infection are:

• Discharge from the penis
• Burning or pain when passing urine
• Pain, discomfort or swelling in one or both testicles (this symptom occurs less often than the first two)

As with women, the symptoms of an infection in the anal area are identical in men: rectal pain, bleeding or discharge may occur.

When should you see a doctor?

If you've had unprotected sex and find out that your partner was infected, see a doctor as soon as possible so you can be treated. The same applies if you notice vaginal or anal discharge, or experience pain or burning when passing urine. In short: with any unusual symptom or change in your intimate area, seeing a doctor is the best decision.

Diagnosing a chlamydia infection

Diagnosis is based on symptoms, medical history and laboratory tests. Both specialists (urologist, gynaecologist, dermatovenereologist) and your GP can diagnose a chlamydia infection.

Diagnostic methods

As well as taking a sexual history and assessing risk factors, the doctor may carry out a clinical examination, including an examination with a speculum and palpation, in order to reach the correct diagnosis. The following tests may also be carried out to confirm the presence of the bacterium Chlamydia trachomatis:

• Laboratory tests based on samples taken: these are the standard molecular tests for diagnosing chlamydia. They're carried out on a secretion sample taken with a swab and confirm the presence of the bacterium with a high degree of accuracy.
• Nucleic acid amplification tests: these are considered the most accurate and effective tests and can be carried out either on a secretion sample (taken by the doctor or by the patient herself) or on a urine sample (which is usually used for diagnosis in men).
• Serological tests: based on blood samples obtained by venepuncture.

Once chlamydia has been diagnosed, tests for other sexually transmitted diseases are also recommended (including syphilis, gonorrhoea and HIV), as is informing your sexual partners.

Treatment with antibiotics

Chlamydia is treatable and curable. Usually the doctor will prescribe an antibiotic and also recommend avoiding sex for at least 7 days after finishing the treatment (or consistently using a condom during that time).

Further recommendations during and after treatment:

• Treating sexual partners too: if infected partners aren't treated as well, you can become reinfected.
• Appropriate intimate hygiene: using an antibacterial intimate gel that doesn't alter vaginal pH and protects the skin barrier, so the intimate area stays clean without causing irritation. The Enroush intimate gel contains 95% natural ingredients, no sulphates and no allergenic fragrances – making it suitable even for sensitive skin.
• Repeating the tests 3 months after the end of treatment: to confirm that the infection hasn't returned.

Possible complications

Left untreated, chlamydia can lead to some serious health problems, particularly in women. In advanced stages, the infection is linked with further conditions:

• In women: pelvic inflammatory disease, abdominal and pelvic pain, ectopic pregnancy and infertility.
• In pregnant women: premature birth.
• In newborns: conjunctivitis and pneumonia.
• In men: epididymitis (a painful infection of the epididymis), prostatitis and, very rarely, infertility.
• In both sexes: joint inflammation (reactive arthritis), conjunctivitis.

 Frequently asked questions about chlamydia infection

Can a chlamydia infection be prevented?

Since the main route of transmission is sexual, the only way to protect yourself from a chlamydia infection is to use barrier methods correctly every time you have sex (a dental dam for oral sex, or a condom for any type of sex). In addition, washing your hands thoroughly every time you touch your own or your partner's intimate area prevents the bacterium from getting into your eyes – and so helps prevent conjunctivitis.

Can chlamydia be transmitted through kissing or other everyday contact?

Chlamydia is only transmitted through intimate contact, i.e. through sex (vaginal, anal or oral), or from mother to baby during birth. The only way it can be passed on through everyday contact is if infected genital secretions come into contact with the eyes.

How long does it take for a chlamydia infection to clear up?

Antibiotic treatment for chlamydia can last 7 to 14 days; a repeat test is then needed after 2 to 3 weeks to confirm that it has cleared. After that, a further test is recommended at 3 months and again at 5 to 6 months, so you know for certain whether the infection has completely gone from your body.

Is sexual abstinence necessary during chlamydia treatment?

Yes, it's recommended to avoid unprotected sex during treatment and for 7 to 10 days afterwards. If abstinence isn't possible, it's essential to use a condom correctly every single time.