Chlamydia spreads through sexual contact. You can get it by having vaginal, anal, or oral sex without a condom with someone who is infected. It is the most commonly reported bacterial sexually transmitted infection in the United States, with chlamydia making up the largest share of the more than 2.2 million STI cases reported to the CDC in 2024.
Vaginal and Anal Sex
The most common way chlamydia spreads is through unprotected vaginal or anal intercourse. The bacteria, called Chlamydia trachomatis, lives in infected genital and rectal fluids. During sex, those fluids come into direct contact with the mucous membranes of a partner’s genitals or rectum, allowing the bacteria to take hold. You don’t need to experience ejaculation for transmission to occur. Simple contact between infected tissue and a partner’s mucous membranes is enough.
Rectal chlamydia can develop from receptive anal sex with an infected partner, but it can also spread from an existing vaginal infection to the rectum without anal sex being involved. This means someone who only has vaginal intercourse can still end up with a rectal infection.
Oral Sex
Chlamydia can infect the throat. Giving oral sex to a partner who has a genital or rectal infection is enough to pick up the bacteria in your mouth or throat. The reverse is also true: receiving oral sex from someone with a throat infection can lead to a genital infection. Throat infections tend to cause fewer problems than genital or rectal ones, but they still matter because a person with chlamydia in their throat can pass it to future partners during oral sex, often without realizing they’re infected.
Eye Infections and Self-Spread
Chlamydia can also infect the eyes. This typically happens through autoinoculation, which simply means transferring the bacteria from one part of your own body to another. If you touch infected genital secretions and then touch your eyes, the bacteria can cause an eye infection known as chlamydial conjunctivitis. Eye exposure can also happen during oral-genital contact. These infections cause redness, discharge, and irritation similar to pink eye, and they need treatment just like a genital infection does.
From Mother to Baby
A pregnant person with chlamydia can pass the infection to their baby during vaginal delivery. As the baby moves through the birth canal, it comes into contact with infected tissue. This can cause eye infections (neonatal conjunctivitis) or pneumonia in the newborn. Routine prenatal screening catches most cases before delivery so they can be treated.
Ways You Cannot Get Chlamydia
Chlamydia bacteria cannot survive long outside the human body. You cannot get chlamydia from a toilet seat, a swimming pool, sharing food, or casual contact like hugging or shaking hands. The bacteria need warm, moist mucous membranes to survive, which is why transmission requires direct sexual contact with infected tissue or fluids. While certain parasites like pubic lice can occasionally spread through contaminated towels or bedding, chlamydia does not work that way.
Why So Many Cases Go Unnoticed
One of the biggest reasons chlamydia spreads so easily is that most people who have it don’t know. About 75% of women and 50% of men with chlamydia have no symptoms at all. That means a person can carry and transmit the infection for weeks or months without any sign that something is wrong. When symptoms do appear, they typically include unusual discharge, burning during urination, or pain during sex, but the absence of symptoms is far more common than their presence.
This is why chlamydia is sometimes called a “silent” infection. Someone can pass it to multiple partners before ever getting tested. Regular screening is the only reliable way to catch it early, particularly for sexually active women under 25, who have the highest infection rates.
How Much Condoms Reduce Your Risk
Consistent condom use significantly lowers the chance of getting chlamydia, though it doesn’t eliminate it entirely. A study published in the American Journal of Epidemiology found that among people with a known infected partner, using condoms every time reduced chlamydia and gonorrhea rates by about 58% compared to inconsistent or no use. That’s a meaningful reduction, but the fact that it’s not 100% reflects the reality that condoms can slip, break, or fail to cover all areas where the bacteria may be present.
Using condoms correctly every time you have vaginal, anal, or oral sex remains the most practical way to lower your risk. Dental dams offer a barrier option during oral sex. Getting tested regularly, especially when you have a new partner, closes the gap that condoms alone can’t fully cover.