Chlamydia spreads through vaginal, anal, or oral sex without a condom with someone who has the infection. It can also pass from a pregnant person to their baby during childbirth, and in rare cases, from one body site to another through touch. What makes chlamydia especially easy to catch is that most people who have it don’t know: roughly 75% of women and 50% of men with chlamydia have zero symptoms.
Sexual Transmission: Vaginal, Anal, and Oral
The bacterium that causes chlamydia thrives on the mucous membranes lining the genitals, rectum, and throat. Any unprotected sexual contact that brings these surfaces together creates an opportunity for transmission. Vaginal and anal sex carry the highest risk, but oral sex can also transmit the infection, particularly when the mouth contacts the penis. Research on the risk from oral contact with the vagina or anus is limited, though the CDC confirms transmission is possible through all forms of oral sex.
Pharyngeal (throat) chlamydia often causes no symptoms at all, which is worth knowing because a person with an active throat infection can pass chlamydia to a partner’s genitals during oral sex without either person realizing anything is wrong.
Rectal chlamydia doesn’t require anal sex. The infection can spread from the vagina to the rectum on its own, meaning someone with a vaginal infection can develop a rectal infection without any anal contact. This is one reason screening often includes multiple body sites.
How Often Chlamydia Spreads Without Symptoms
The single biggest factor driving chlamydia transmission is that the majority of infected people feel completely fine. Three out of four women and half of men with chlamydia experience no symptoms whatsoever. They don’t know they’re infected, so they don’t seek treatment, and they unknowingly pass the bacteria to partners. This is why chlamydia is sometimes called a “silent” infection.
When symptoms do appear, they typically show up one to three weeks after exposure, though they can take longer. In women, symptoms may include unusual vaginal discharge, burning during urination, or bleeding between periods. In men, the most common signs are discharge from the penis, burning with urination, or pain in the testicles. But again, most people never notice any of these.
With over 1.5 million cases reported in the United States in 2024 alone, and women affected at nearly twice the rate of men (549.5 per 100,000 women versus 335.3 per 100,000 men), the scale of silent transmission is enormous. The actual number of infections is likely much higher, since many go undiagnosed.
Transmission During Pregnancy and Childbirth
A pregnant person with an untreated chlamydia infection can pass the bacteria to their baby as the infant moves through the birth canal during vaginal delivery. The most common result is conjunctivitis, a bacterial eye infection that typically appears in the first two weeks of life. Chlamydia can also cause pneumonia in newborns, usually developing within the first few months.
This is why routine chlamydia screening during pregnancy is standard practice. Treatment before delivery prevents transmission to the baby entirely.
Spreading It to Your Own Eyes
Chlamydia can infect the eyes, and this doesn’t always require another person. If you have an active genital infection and touch your genitals, then touch your eyes without washing your hands, you can transfer the bacteria yourself. This is called auto-inoculation. The infection can also spread through contaminated towels or bedding, though this is less common. Chlamydial eye infections cause redness, discharge, and irritation, and they need antibiotic treatment to avoid potential damage to the eye.
Ways You Cannot Get Chlamydia
The bacteria that cause chlamydia cannot survive long outside the human body. You cannot get chlamydia from toilet seats, doorknobs, swimming pools, shared clothing, or casual contact like hugging or shaking hands. The chance of contracting any STI from a hard surface like a toilet seat is essentially zero. Chlamydia requires direct contact with infected mucous membranes or fluids from those membranes.
You also cannot get chlamydia from kissing, sharing food, or breathing the same air as someone who’s infected. It is a sexually transmitted infection in the truest sense: it requires sexual or intimate physical contact with infected tissue.
How Condoms Reduce Your Risk
Consistent, correct condom use cuts the odds of chlamydia transmission by about 60%, based on research in a study published in JAMA Pediatrics that controlled for other risk factors. That’s a meaningful reduction, though it’s not as close to 100% as many people assume. The reason condoms aren’t fully protective is that chlamydia can infect areas a condom doesn’t cover, and any inconsistency in use (putting it on late, for example) lowers the benefit substantially.
Regular screening remains the most effective way to catch and stop the infection early, particularly for sexually active women under 25 and anyone with new or multiple partners. A simple urine test or swab is all that’s needed, and chlamydia is fully curable with a short course of antibiotics. Both you and your partner need treatment at the same time to prevent passing the infection back and forth.