Causes and Risk Factors of Chlamydia

Chlamydial diseases are sexually transmitted and caused by the bacterium Chlamydia trachomatis. However, this bacterium acts more like a virus. This can affect the way chlamydia infection is transmitted and the risk factors that are important in acquiring it. Chlamydia infections can affect the vagina, cervix, and rectum, among other areas.

Fortunately, chlamydia is a largely preventable infection. Learning how its namesake bacteria behave can help you get a better understanding of what makes an infection more likely. 

chlamydia risk factors
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Chlamydia Bacteria

Most bacteria are capable of reproducing on their own as long as they're in a hospitable environment—but not the type associated with chlamydia. Chlamydia bacteria must rely on its hosts (humans) to survive, much like a virus does.

Essentially, chlamydia treats the insides of human cells like great big grocery stores. It takes ATP, an energy molecule; nutrients; and other supplies—essentials for reproduction that the bacteria can't make on their own—from the person it's infecting.

Since the bacteria can't live without these necessities, C. trachomatis is an obligate (can't survive without) intracellular (living inside cells) parasite (where it takes but does not give back).


Chlamydia basically has a two-phase life cycle: the elementary body and reticulate body stages.

Elementary Body

Chlamydia travels between cells, and between people, in the form of an elementary body—a small, dense, spore-like structure.

In this stage, this elementary body doesn't do much of anything. Bacteria travel between cells and between people to create new infections, but these bodies don't replicate or change. They are just carried around in bodily fluids.

Chlamydia is infectious, but not active in this stage.

Reticulate Body

Chlamydia enters this stage once the elementary body infects a new cell. In this form, the bacteria use supplies from the host cell to make copies of itself inside the cell.

Reticulate bodies can grow, divide, and metabolize. Infections can persist in this manner for a while.

Once there are enough copies—too many to survive inside the cell—reticulate bodies can turn back into elementary bodies, burst the host cell open, and escape to infect new cells (either in the infected individual or a sexual partner). This starts the process all over again.

This is a pretty strange life cycle that doesn't really follow the roadmap for either a bacterial or viral infection. That is one of the reasons that chlamydia is so interesting and important to study.


Discussing the characteristics of chlamydia is important because they affect the way the bacteria are transmitted from person to person. The method of transmission, in turn, affects the risk factors that make it more likely a person will contract the infection.

Chlamydia is transmitted through secretions rather than skin-to-skin contact, as is the case with some microorganisms (such as human papillomavirus, or HPV). This means it is less likely to pass between two people without some form of bodily fluid, such as semen or cervical mucus, present. It also means that condoms can be very effective at preventing the spread of the bacteria.

Understanding the elementary body stage also helps clarify why sometimes chlamydia infections are present for months or even years before they are detected. This is especially important if you have a partner who, upon learning of your chlamydia diagnosis, wonders how you became infected despite being in a committed sexual relationship with them for a lengthy period of time.

The risk factors for chlamydia are similar to the risk factors for sexually transmitted infections (STIs) and sexually transmitted diseases (STDs) in general, but can vary somewhat based on the method of transmission.

Lifestyle Risk Factors

Certain lifestyle practices can increase your risk of chlamydia infection:

  • Unprotected sex: Engaging in either vaginal, receptive anal, or oral sex without a condom is the greatest risk factor for developing chlamydia. Since the bacteria is spread by secretions, using a condom every time you have sex (unless you're in a long-term monogamous relationship in which both partners have tested negative) is the best way to avoid an infection.
  • Having multiple sex partners: The more sex partners a person has, the more likely it is that they will develop a sexually transmitted disease, including chlamydia. Of course, it only takes one sex partner to transmit the infection, and practicing safe sex is important no matter your sexual practices.
  • A partner who has an STD: Obviously, an untreated partner poses a risk. But there is also a risk of transmission if a partner has not yet finished a full seven-day course of antibiotics, or if they received a single-dose medication and seven days have not yet passed.
  • Men who have sex with men (MSM): Men who have sex with men are more likely to develop genital, rectal, and/or oral chlamydia infection than heterosexual men. In a study, 11.8% of MSM in an urban area of the United States were found to have extragenital chlamydia infections involving either the anus or the throat.

Health Risk Factors

People with certain existing health concerns are at greater risk for chlamydia infection than others.

Health risk factors include:

  • Having other STIs/STDs: Lifestyle practices that can predispose you to another STI/STD can also raise your risk of chlamydia (and vice versa). Many STI/STDs also cause inflammation of the sensitive mucosa of the vagina, cervix, or urethra. When this tissue is compromised due to one infection, it's easier for another microorganism to enter the body and begin to grow.
  • Being HIV positive: Up to 10% of men who are HIV positive will also test positive for chlamydia.
  • Having cervical ectopy: Cervical ectopy, a condition in which the cells of the endocervix (cervical canal) are instead found on the ectocervix (outside the cervical canal), increases the susceptibility of the tissue to chlamydial infection. This condition is more common in young women. An older study looking at women age 15 to 24 found that those with cervical ectopy were almost twice as likely to test positive for chlamydia. As women age, the cervical tissue migrates and cervical ectopy usually goes away, putting them at lower risk for chlamydia.

Untreated mothers can also pass chlamydia to their babies during birth.


Unlike some infections, in which a person develops immunity after exposure, the body does not develop any immunity against chlamydia after an infection. This means that you can be infected over and over again. 


Reducing your risk of contracting chlamydia and practicing safe sex begins with choosing your sex partners wisely.

While asking a potential partner about previous diagnoses may not exactly be something you'd like to do, know that people are having these important conversations much more often now than in the past. Protecting your health is nothing to feel embarrassed about.

The most effective way to prevent chlamydia, specifically, is to use a condom each and every time you have vaginal or anal sex.

Reducing your risk with oral sex is also possible. Condoms can be used during fellatio, and dental dams or other barriers can be used during rimming or cunnilingus.

Even if you are careful, it's still important to see your healthcare provider regularly and undergo routine screening for chlamydia. Only 5% to 30% of infections in women and only 10% of infections in men cause symptoms. Being tested is the only way to know if you're infected for sure—and to prevent the complications of an untreated case.

The Doctor Discussion Guide below can help you start that conversation 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

Frequently Asked Questions

  • What causes chlamydia?

    Chlamydia is a sexually transmitted infection (STI) caused by the bacteria Chlamydia trachomatis. This specific type of bacteria is unique in that it behaves like a virus in that it relies on a human host to survive and replicate. This also affects the way the infection is transmitted.

  • How do you get chlamydia?

    Chlamydia is transmitted through unprotected vaginal, anal, or oral sex. It is passed via bodily secretions, such as semen or cervical mucus (but not saliva), meaning it is unlikely to pass from person to person through skin-to-skin contact alone. Certain lifestyle factors can increase your risk:

    • Engaging in unprotected sex
    • Having multiple sex partners
    • Having another STI or having a partner who has an STI
    • Men who have sex with men (MSM)
    • Being HIV positive
    • Having cervical ectopy
  • How long can chlamydia go untreated before it causes damage?

    There's no specific timeline, but the longer chlamydia goes untreated, the more damage can occur from complications such as pelvic inflammatory disease. Known as a silent disease, chlamydia presents with symptoms in only about 5% to 30% of cases in women and only about 10% of cases in men, which means the infection may often go untreated for a while before it's discovered. When symptoms do appear, they usually don't show up until three weeks after the initial exposure.

  • Can you get chlamydia without being sexually active?

    No. Chlamydia is passed only through sexual contact with an infected person, but ejaculation does not have to occur for transmission. However, chlamydia may also be spread from an untreated mother to her newborn during birth.

  • Can you get chlamydia more than once?

    Yes. Unlike some other infections, the body does not form immunity to chlamydia, which means infections can keep occurring. Fortunately, it can be treated with antibiotics.

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4 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.
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  2. Centers for Disease Control and Prevention. Chlamydia—CDC fact sheet (detailed).

  3. Trebach JD, Chaulk CP, Page KR, Tuddenham S, Ghanem KG. Neisseria gonorrhoeae and Chlamydia trachomatis among women reporting extragenital exposures. Sex Transm Dis. 2015;42(5):233-9. doi:10.1097/OLQ.0000000000000248

  4. Jones J, Weiss K, Mermin J, et al. Proportion of incident human immunodeficiency virus cases among men who have sex with men attributable to gonorrhea and chlamydia: A modeling analysis. Sex Transm Dis. 2019;46(6):357-363. doi:10.1097/OLQ.0000000000000980

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