What Is Chlamydia?

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Chlamydia, an infection caused by the bacterium Chlamydia trachomatis, is the most common curable sexually transmitted infection (STI) in the United States. It may occur at any age but is most common in young people. You may not know you have chlamydia, as it often doesn't cause symptoms. While some are diagnosed because they seek an evaluation of symptoms such as discharge or pain, others are only diagnosed as part of routine health screening. There is no immunity to chlamydia, so reinfection is common. Chlamydia is treatable, but routine testing is obviously essential to identify an infection.

Chlamydia Bacteria Overview
Verywell / Emily Roberts


It's estimated that approximately 1.7 million people in the United States will be diagnosed with the infection each year, with two-thirds of infections occurring in people between the ages of 15 and 24. The actual incidence is likely higher, however, given that the majority of people do not have symptoms.

Chlamydia is diagnosed almost twice as often in women than men. However, this may be because women are more likely to be screened.

Catching the infection in so many women is a good thing, of course, but disproportionate screening also means that there are too many sexual partners of infected women who are not being treated. 

Chlamydia has been a reportable disease in the United States since 1994 but has only been regularly reported since 2000. The incidence of chlamydia has been increasing, though it's not certain if this is an actual increase or due to better detection.

The Genitalia

In order to best understand the symptoms of chlamydia, it's helpful to briefly review the female and male genitalia.

The female reproductive system consists of the vagina, the uterus, the cervix (the opening between the vagina and the uterus), the fallopian tubes, and the ovaries.

The cervix is the site of chlamydial infections in 75-80% of women.

From there, bacteria can travel through the uterus and up into the tubes, ovaries, and surrounding structures causing an infection known as pelvic inflammatory disease (PID).

The male reproductive system consists of the penis, the testes, the prostate gland, and associated ducts. Chlamydia infections in men often affect the urethra (the tube running from the bladder to the tip of the penis). From this location, the bacteria can travel to the epididymis—a tube that resides behind the testicles—resulting in a condition known as epididymitis.

Types of Chlamydial Infections

There are two other types of chlamydial infections in addition to standard genital infections, though these are less common in the United States.

Lymphogranuloma Venereum: Chlamydia also causes a sexually transmitted infection called lymphogranuloma venereum, which has symptoms much different than standard genital chlamydia infections. It has historically been thought of as a condition found in third-world countries, but its incidence is increasing worldwide, including in the United States. It is more common in MSM, and the symptoms are similar to syphilis. It is caused by chlamydia serovars (types) L1, L2, and L3. 

Trachoma: Trachoma is an eye infection caused by the chlamydia bacteria known as serovars A through C. Unlike genital infections and lymphogranuloma venereum, trachoma is not considered to be an STI. While it is uncommon in the United States, it is the leading infectious cause of blindness worldwide. It is caused by autoinoculation (when people touch a surface containing the bacteria and then touch their eyes) and can be spread by hands, clothing, bedding, or even flies.

Chlamydia Symptoms

The symptoms of chlamydia vary between men and women, and also with the location of the infection. Often, people with chlamydia don't have any symptoms. Even when that's the case, the infection can still damage the reproductive system. Screening is often done to detect asymptomatic infection.


It's estimated that only 5 percent to 30 percent of women who are infected with chlamydia will have symptoms. The most common symptom is vaginal discharge, which can be thin or thick, clear or colored (often yellow). Women may also notice redness, swelling, burning, or itching of the vulva and vaginal area.

Pain and burning with urination may occur, and urination frequency may increase. Involvement of the cervix can cause pain with sex (dyspareunia) and bleeding between periods.

When the infection travels to the fallopian tubes and pelvis, abdominal and back pain, as well as flu-like symptoms such as a fever, may occur.

Chlamydia is known as the "silent infection" because symptoms are not always present.


It's estimated that only 10 percent of men will have symptoms related to chlamydia infection. When present, symptoms may include pain and burning during urination as well as urinary frequency.

There may be redness, swelling, and itching around the opening of the penis, as well as discharge from the penis (which can vary from clear and watery to thick and yellow-green).

Pain with ejaculation may occur as well. When the infection travels to the epididymis, it may cause pain and swelling in one or both testicles. 

Other Symptoms (Both Sexes)

Chlamydia infections may also be transmitted via receptive anal sex or oral sex.

With anal sex, symptoms of infection may include rectal pain, bleeding, discharge, and a feeling of incomplete emptying of the bowels (tenesmus).

Chlamydia can be transmitted during oral sex. Most people with oral chlamydia don’t have any symptoms, though some might have some soreness and redness in their throat or mouth.

One study of urban regions in the United States found 4% of women, 1.6% of men, and 12% of men who have sex with men (MSM) have extragenital chlamydia.

Other studies have found that the incidence of rectal and oral chlamydia in MSM is 3 percent to 10 percent and 0.5 percent to 2.3 percent, respectively.


Genital chlamydia infections are caused by serovars (types of chlamydia bacteria) D through K. There are other forms of chlamydia as well, which are less common in the United States.

Chlamydia is transmitted through secretions (not skin-to-skin contact like some, STIs/STDs) and can occur through vaginal, anal, or oral sex. The bacteria can also be transmitted from mother to infant during vaginal delivery.

Ejaculation is not necessary to spread chlamydial infection.

Symptoms, when they occur, usually appear around three weeks after exposure, though complications such as PID can occur much later.

Chlamydia acts more like a virus than a bacterium in some ways and is an obligate intracellular parasite, meaning that it has to stay inside of human cells to stay alive.


Chlamydia may be suspected based on symptoms or a physical exam, but it can be difficult to distinguish chlamydia from some other STIs (such as gonorrhea) based on symptoms alone. Laboratory testing is needed to make an official chlamydia diagnosis.

In the absence of symptoms, a person can go months if not years without realizing they have chlamydia. For this reason, routine screenings (such as an annual gynecological exam) are essential to diagnosing and treating the infection, therefore preventing its spread.

A chlamydia diagnosis is usually made after a healthcare professional considers one's medical history (including a history of exposure and sexual activity), performs a physical exam, and runs either a urine test or, as an alternative in women, a test on a sample collected from swabbing of the endocervical canal or vagina.


Since chlamydia is so often asymptomatic, routine screening is highly recommended. This includes yearly screening for sexually active women age 25 and under and older women who have risk factors

Guidelines for sexually active MSM also recommend regular screening for chlamydia—at least annual or biannual, depending on risk. This involves testing of the throat, urine, and rectum, along with other STIs (hepatitis B, hepatitis C, and syphilis, for example).

Chlamydia is a nationally notifiable disease and reporting is important to understand more about the infection.


Chlamydia is treated with prescription antibiotics; there are currently no effective over-the-counter or home remedies. There are recommended treatments and alternative options for both adults and pregnant women.

When a person is diagnosed with chlamydia, all sexual partners they have had within the last 60 days must also be screened and treated.

You must take all of the medication prescribed to you to eradicate the bacteria, and prescriptions should not be shared.

It is recommended that people abstain from sex for seven days after treatment has begun.


There are several potential complications that can occur if chlamydia is left untreated.


The most common complication in women is PID, a condition that occurs in 10 percent to 15 percent of untreated women. In addition to causing discomfort, the infection can scar the fallopian tubes and surrounding structures, leading to chronic pelvic pain, infertility, and ectopic (tubal) pregnancy, a life-threatening condition.

Chlamydia infection can increase the risk of developing or transmitting HIV for both men and women.


Infections that extend to the epididymis in men can also cause scarring. This may lead to chronic pain and possible infertility. Rarely, men may develop a syndrome of joint inflammation in one or more joints, inflammation of the urethra, or inflammation of the eye.

Pregnant Women

Untreated infections during pregnancy are associated with a higher rate of premature birth and stillbirth. Babies who are born to mothers with untreated chlamydia may develop eye infections or pneumonia.

Those Who Have Anal Sex

Scarring of the rectum due to chlamydia infection can lead to chronic rectal pain and, rarely, rectal fistulas.


As with all sexually transmitted diseases, the best way to prevent chlamydia is to use a condom unless you are in a long-term, monogamous relationship with someone who has been tested and had negative results.

Lifestyle measures that are helpful include:

  • Limiting your number of sexual partners
  • Having "the conversation" about STIs/STDs before you have sex
  • Being screened regularly.

It's important to avoid douching, as this could increase the risk of PID in infected women.

A Word From Verywell

Receiving a diagnosis of chlamydia can be unsettling, especially if you aren't certain where you contracted the infection or how long you've been infected.

While having more sexual partners is a risk factor for chlamydia, it only takes one sexual partner to become infected.

There is a stigma about STIs/STDs that often causes people to feel shame, perhaps about their sexual past. Remember that chlamydia is very common and that your healthcare provider only cares about your wellness.

Untreated chlamydia can cause complications, some of which can be serious. But the bottom line is that the infection is easy to test for, is very treatable, and often preventable. Our Doctor Discussion Guide below can help you start a conversation about prevention, testing, and more with a healthcare professional.

Chlamydia Doctor Discussion Guide

Get our printable guide for your next doctor's appointment to help you ask the right questions.

Doctor Discussion Guide Woman
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Article Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Centers for Disease Control and Prevention. Chlamydia - CDC Fact Sheet (Detailed)

  2. World Health Organization. Trachoma

  3. Planned Parenthood. Chlamydia

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