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. With over 1.5 million cases reported in the United States in 2024 alone, it remains one of the most common sexually transmitted infections, largely because the majority of people who carry it have no idea they’re infected.
Vaginal and Anal Sex Are the Primary Routes
The bacteria that cause chlamydia, called Chlamydia trachomatis, live in bodily fluids like semen, pre-ejaculate, and vaginal fluids. Transmission happens when these fluids come into contact with the mucous membranes of a partner’s genitals, rectum, or throat. Vaginal and anal intercourse are by far the most common ways this occurs, because those types of sex involve prolonged, direct contact between mucous membranes and infected fluids.
Rectal chlamydia can develop from receptive anal sex, but it can also spread from an existing vaginal infection to the rectum without anal sex taking place. This means someone who has never had anal intercourse can still develop a rectal infection.
Oral Sex Carries a Lower but Real Risk
Giving oral sex to a partner with a genital or rectal chlamydia infection can lead to a throat (pharyngeal) infection. The risk is generally considered lower than with vaginal or anal sex, though researchers note it’s difficult to compare precise risk levels across different types of sexual contact. A chlamydia infection in the throat may cause fewer direct complications than one in the genitals or rectum, but it can still be passed to other partners through oral sex, keeping the chain of transmission going.
Factors like poor oral health, mouth sores, or exposure to semen may theoretically increase risk during oral sex, but no studies have confirmed this definitively.
What About Sex Toys and Non-Penetrative Contact?
Chlamydia spreads through direct exchange of bodily fluids, so the likelihood of getting it through indirect contact, like a shared sex toy, is low. That said, it’s not impossible. The risk increases if a toy is inserted into the body, if it’s made from porous materials like neoprene or vinyl that trap fluids, or if it’s shared between partners without being cleaned. The bacteria can’t survive outside the body for very long, which limits how effectively toys or other objects can act as carriers.
You can also transfer the bacteria from one part of your body to another with your hands. Touching infected genital fluids and then touching your eyes, for example, can cause a chlamydial eye infection. This type of self-transmission is uncommon but well documented.
You Cannot Get Chlamydia From a Toilet Seat
The bacteria that cause chlamydia cannot survive on hard surfaces like toilet seats, doorknobs, or pool surfaces. There is virtually zero chance of contracting the infection this way. The same goes for sharing utensils, clothing, or casual physical contact like hugging or handshakes. Chlamydia requires warm, moist mucous membranes to survive, and it dies quickly once exposed to the open environment. Contaminated fabrics like sheets or towels carry an extremely low theoretical risk, but only if they’re freshly soiled and come into direct contact with mucous membranes.
Most People With Chlamydia Have No Symptoms
This is the single most important fact about how chlamydia spreads so effectively: 75% of women and 50% of men with the infection have no symptoms at all. That means the majority of cases go undiagnosed and unreported. A sexual partner can look and feel perfectly healthy and still transmit the infection. There’s no way to tell by appearance whether someone is carrying chlamydia.
When symptoms do appear, they typically show up one to three weeks after exposure, though some people don’t develop symptoms for months. In women, symptoms can include unusual vaginal discharge, burning during urination, or bleeding between periods. In men, common signs are discharge from the penis, burning with urination, or pain and swelling in one or both testicles. Rectal infections may cause discharge, pain, or bleeding, regardless of gender.
Transmission During Childbirth
A pregnant person with an untreated chlamydia infection can pass the bacteria to their baby as it moves through the birth canal. This can cause eye infections or pneumonia in the newborn. Routine prenatal screening catches most cases before delivery, and treatment with antibiotics during pregnancy is safe and effective at preventing transmission.
Reinfection Is Extremely Common
Getting treated for chlamydia does not make you immune. Reinfection rates are high, and the most common reason is that a sexual partner wasn’t treated at the same time. If you complete your antibiotics but your partner still carries the bacteria, you’ll likely get reinfected the next time you have unprotected sex. Studies consistently show that the majority of repeat chlamydia cases aren’t treatment failures. They’re reinfections from untreated partners or new partners who are unknowingly carrying the bacteria.
This is why treatment guidelines emphasize that all recent sexual partners need to be notified and treated simultaneously. Resuming sexual activity before both partners have completed treatment restarts the cycle.
Who Is Most at Risk
Anyone who is sexually active can get chlamydia, but certain groups face higher rates. Women are diagnosed nearly twice as often as men, with a rate of about 550 cases per 100,000 people compared to 335 per 100,000 for men in 2024 provisional data. Some of that gap reflects the fact that women are screened more regularly, but biological factors also play a role: the cervix is particularly susceptible to chlamydial infection.
Sexually active people under 25 account for a disproportionate share of cases. Having multiple partners, inconsistent condom use, or a previous chlamydia infection all increase risk. Because the infection is so often silent, the only reliable way to know your status is through testing, which involves a simple urine sample or swab.