Chlamydia spreads through sexual contact, specifically 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 delivery. You cannot get chlamydia from toilet seats, shared surfaces, or casual contact like hugging or shaking hands.
Vaginal and Anal Sex
Vaginal and anal intercourse are the most common ways chlamydia is transmitted. The bacteria that cause chlamydia live in the mucous membranes of the genitals and rectum, so any unprotected contact between these areas can pass the infection. The estimated transmission risk per single act of unprotected sex is around 10%, with a median probability of about 9.5% in modeling studies. That may sound low for a single encounter, but repeated exposure adds up quickly, and most sexual relationships involve more than one encounter.
Rectal infections can happen through receptive anal sex, but they can also develop when the bacteria spread from an infected vagina to the rectum without any anal contact at all. This means a person can have chlamydia in more than one site simultaneously without realizing it.
Oral Sex
Chlamydia can infect the throat after giving oral sex to a partner with a genital or rectal infection. A throat infection may also work in reverse: having chlamydia in the throat can make it easier to pass the bacteria to a partner’s genitals during oral sex. Pharyngeal chlamydia often produces no symptoms, so many people who carry it in the throat never know.
Throat infections may cause fewer complications than genital or rectal infections, but they still sustain the chain of transmission. Standard screening tests don’t always check the throat unless you specifically request it.
Why Asymptomatic Infection Matters
Roughly 61% of chlamydia infections produce no symptoms at all. That’s more than half of all cases where the infected person feels completely fine and has no visible signs of infection. Without symptoms, people don’t seek testing, don’t get treated, and continue having sex while unknowingly passing the bacteria to partners. This is the single biggest driver of chlamydia’s spread.
Even without symptoms, the bacteria are present in genital and rectal secretions and can be transmitted during any unprotected sexual contact. The infection doesn’t need to cause discharge, burning, or pain to be contagious. Untreated infections sustain transmission indefinitely until the person is tested and treated.
Transmission During Childbirth
A pregnant person with untreated chlamydia can pass the infection to their baby during vaginal delivery. As the baby moves through the birth canal, the bacteria can infect the newborn’s eyes, causing a type of conjunctivitis, or the lungs, leading to respiratory infection. Chlamydia during pregnancy has also been linked to premature rupture of membranes, preterm delivery, and low birth weight. Prenatal screening catches most cases before delivery, allowing treatment with antibiotics that clear the infection well before labor.
Hand-to-Eye Spread
Chlamydia can reach the eyes when infected genital secretions are transferred by hand. If you touch your own or a partner’s infected genitals and then touch your eye, the bacteria can establish an infection in the conjunctiva, the thin membrane lining the inner eyelid. This form, called adult inclusion conjunctivitis, causes redness, discharge, and swelling that can persist for weeks if untreated. It’s uncommon compared to genital infection but worth knowing about, especially since simple handwashing after sexual contact prevents it.
Shared Sex Toys
Sharing sex toys can transmit chlamydia if the toy carries infected secretions from one person’s body to another’s. The NHS recommends washing sex toys between each use and placing a fresh condom on them before each person uses them. The risk is essentially the same as direct genital contact: if infected fluids reach mucous membranes, the bacteria can take hold.
What Doesn’t Spread Chlamydia
Chlamydia bacteria cannot survive outside the body’s mucous membranes. They die almost immediately on dry surfaces, in open air, and in water. You cannot contract chlamydia from a toilet seat, a swimming pool, shared towels, doorknobs, or any form of casual contact. Hugging, kissing on the cheek, sharing food, and sitting next to someone pose zero risk. The bacteria require direct contact with mucous membranes (genitals, rectum, throat, or eyes) to establish an infection.
How Common Chlamydia Is
In 2024, more than 1.5 million chlamydia cases were reported in the United States alone, with women accounting for roughly 944,000 of those and men about 564,000. The overall rate was about 446 cases per 100,000 people. These numbers actually represent a decline, down 8% from 2023, but chlamydia remains the most frequently reported bacterial sexually transmitted infection in the country. Because the majority of cases are asymptomatic, the true number of infections is likely substantially higher than what’s reported.
The gap between male and female case counts largely reflects screening patterns rather than biology. Women are more likely to be screened during routine gynecological visits, so more of their infections get caught and counted. Men with asymptomatic infections often go undiagnosed for longer.
Reducing Your Risk
Condoms, when used consistently and correctly during vaginal, anal, and oral sex, significantly lower the chance of transmission. Since most chlamydia infections cause no symptoms, regular screening is the most reliable way to catch and stop an infection before it spreads. Annual screening is generally recommended for sexually active women under 25 and for anyone with new or multiple partners. Testing typically involves a simple urine sample or a swab, and results come back within a few days. If you test positive, a short course of antibiotics clears the infection, and your sexual partners from the preceding 60 days should be notified and tested as well.