A female can get chlamydia through vaginal, anal, or oral sex without a condom with someone who has the infection. The bacteria that cause chlamydia, called Chlamydia trachomatis, spread through infected genital secretions, meaning any sexual contact that involves these fluids can transmit the infection. Roughly 75% of women with chlamydia have no symptoms at all, which is why many people don’t realize they have it or that their partner has it.
Vaginal Sex Is the Most Common Route
Unprotected vaginal intercourse is the primary way women contract chlamydia. The bacteria infect the cells lining the cervix, which is the opening to the uterus. From there, the infection can spread upward into the uterus and fallopian tubes if left untreated. Research estimates the per-encounter transmission probability at about 4.5% for a single unprotected sexual act, though that number can vary depending on factors like how long the infected partner has carried the bacteria and whether other infections are present.
That 4.5% figure might sound low for a single encounter, but the risk compounds quickly over repeated exposures. A few weeks of unprotected sex with an infected partner makes transmission likely. And because chlamydia so often produces no symptoms in either partner, many couples have no idea the bacteria are being passed back and forth.
Anal and Oral Sex Also Carry Risk
Chlamydia can infect the rectum through receptive anal sex. It can also reach the rectum without anal sex at all, spreading from an existing vaginal infection to nearby tissue through a process called autoinoculation. This matters because a rectal infection that goes undetected can reinfect the vagina even after treatment, creating a cycle of repeat infections.
Oral sex can transmit chlamydia to the throat, though this is less common than vaginal or anal transmission. A throat infection is usually mild or symptom-free and often clears on its own, but it can still be passed to a partner’s genitals during oral contact.
Shared Sex Toys and Genital Contact
Because chlamydia spreads through infected secretions rather than through blood or airborne particles, any object or surface that carries those secretions can theoretically transfer the bacteria. Sharing sex toys without cleaning them or using a new barrier between partners is one plausible route. The bacteria don’t survive long outside the body, so casual contact like sharing towels, toilet seats, or clothing does not spread chlamydia.
Transmission During Childbirth
A pregnant woman with an active chlamydia infection can pass it to her baby during vaginal delivery. In newborns, this can cause eye infections or pneumonia. This is one reason routine chlamydia screening is standard during prenatal care.
Why So Many Cases Go Unnoticed
Chlamydia is often called a “silent” infection. About three out of four women who contract it never develop noticeable symptoms. When symptoms do appear, they typically show up one to three weeks after exposure, though they can take longer. The most common signs include unusual vaginal discharge, a burning feeling when urinating, and bleeding between periods. But the absence of symptoms doesn’t mean the infection is harmless. Untreated chlamydia can progress to pelvic inflammatory disease, which can damage the fallopian tubes and lead to chronic pain, ectopic pregnancy, or infertility.
The silent nature of the infection also explains why it’s so widespread. Provisional CDC data from 2024 recorded nearly 944,000 chlamydia cases in women in the United States alone, a rate of about 550 cases per 100,000 women. The actual number is almost certainly higher, since many infections are never diagnosed.
Reinfection Is Extremely Common
Getting treated for chlamydia doesn’t protect you from catching it again. In fact, reinfection is one of the biggest challenges with this STI. The majority of repeat infections aren’t treatment failures. They happen because a partner wasn’t treated at the same time, or because a person begins a new sexual relationship with someone who carries the bacteria. Untreated rectal chlamydia in women who were treated only for a cervical infection is another overlooked source of reinfection, since the bacteria can spread back from the rectum to the vagina on their own.
Repeat infections raise the risk of serious complications like pelvic inflammatory disease with each occurrence. The CDC recommends retesting about three months after treatment, regardless of whether you think your partner was also treated.
How to Lower Your Risk
Latex condoms, used consistently and correctly, reduce chlamydia transmission by acting as a physical barrier against the genital secretions that carry the bacteria. They aren’t perfect, since contact can occur around areas the condom doesn’t cover, but they significantly lower the odds. Using condoms or dental dams during oral sex adds another layer of protection, particularly with new or untested partners.
Annual screening is recommended for all sexually active women under 25, and for older women with risk factors like new or multiple partners. Because the infection so rarely announces itself with symptoms, routine testing is the most reliable way to catch it early. A simple urine test or vaginal swab is all it takes, and treatment with a short course of antibiotics clears the infection in the vast majority of cases. If you test positive, your sexual partners from the past 60 days should also be tested and treated to break the chain of transmission.