Chlamydia spreads through vaginal, anal, or oral sex with someone who has the infection. It’s the most commonly reported bacterial sexually transmitted infection in the United States, and the reason it spreads so easily is that most people who have it don’t know they’re infected. About 75% of women and 50% of men with chlamydia have no symptoms at all.
Sexual Contact Is the Primary Route
The bacterium that causes chlamydia lives in certain body tissues, particularly the cervix, urethra, rectum, and throat. It passes from one person to another through contact with infected fluids during sex. You can catch it through vaginal sex, anal sex, or oral sex without a condom or dental dam. Penetration doesn’t have to result in ejaculation for transmission to occur. Skin-to-mucous-membrane contact with infected genital fluids is enough.
Rectal infections happen either through receptive anal sex or when the bacteria spreads from another infected site, like the vagina. Throat infections from chlamydia are less common but can result from giving oral sex to an infected partner. These non-genital infections often produce no symptoms, which makes them easy to miss during routine screening that only tests urine or genital swabs.
Why So Many People Spread It Without Knowing
The single biggest factor driving chlamydia transmission is that the infection is usually silent. Three out of four women and half of men with chlamydia experience no symptoms whatsoever. That means a person can carry and transmit the bacteria for weeks or months without any reason to suspect they’re infected. When symptoms do appear, they typically show up 7 to 21 days after exposure, though in some cases the incubation period stretches to several months.
For women, symptoms might include unusual vaginal discharge, burning during urination, or bleeding between periods. Men may notice discharge from the penis, burning when urinating, or pain and swelling in one testicle. But again, the absence of symptoms is far more common than their presence, which is why regular screening is the only reliable way to catch the infection early.
Ways You Cannot Catch Chlamydia
Chlamydia requires specific human tissue to survive. The bacterium cannot live on surfaces like toilet seats, doorknobs, bath towels, or bed linens. Even if a droplet of infected fluid landed on a surface, the organism would need to reach suitable tissue (such as the cervix, urethra, or the surface of the eye) before it dried out. In practical terms, this makes casual surface transmission essentially impossible. You also cannot catch chlamydia from hugging, sharing food, coughing, or swimming pools.
Transmission During Childbirth
A pregnant woman with chlamydia can pass the infection to her baby during vaginal delivery. As the newborn moves through the birth canal, the bacteria can infect the baby’s eyes or lungs. This can lead to eye infections (neonatal conjunctivitis) or pneumonia in the first weeks of life. Prenatal screening catches most cases before delivery, allowing treatment that protects both mother and baby.
How Condoms Reduce Your Risk
Correct and consistent condom use cuts the odds of catching chlamydia by roughly 60%, based on research published in JAMA Pediatrics that studied urban adolescents. That’s meaningful protection, but it’s not 100%, partly because condoms don’t cover all genital skin and partly because real-world use isn’t always perfectly consistent. Still, condoms remain one of the most effective tools available for reducing transmission of chlamydia and other STIs during any type of sex.
For oral sex, dental dams or condoms provide a barrier between the mouth and genitals. These are used less frequently in practice, which is one reason throat and rectal infections often go undetected.
Reinfection Is Common
Getting treated for chlamydia doesn’t protect you from catching it again. Reinfection rates are high, and most repeat cases aren’t treatment failures. They happen because a partner wasn’t treated at the same time, or because a person begins having sex with a new partner who is infected. This cycle is common enough that the CDC recommends retesting about three months after treatment, regardless of whether you believe your partner was also treated.
If both partners aren’t treated simultaneously, the bacteria simply passes back and forth. This is sometimes called a “ping-pong” pattern of reinfection. Anyone diagnosed with chlamydia should notify recent sexual partners so they can get tested and treated before resuming sexual contact.
Who Should Get Tested
Because chlamydia so rarely announces itself with symptoms, screening guidelines exist for people at higher statistical risk. Sexually active women under 25 should be tested annually. Women 25 and older should be tested if they have a new partner, multiple partners, or a partner who has tested positive. Men who have sex with men should be screened at least annually at all sites of contact (urethra, rectum, throat). Anyone with a new sexual partner or multiple partners benefits from routine testing, regardless of gender.
Testing is straightforward. A urine sample or a swab of the infected site is all that’s needed, and results typically come back within a few days. If you test positive, treatment with a short course of antibiotics clears the infection in the vast majority of cases. The key is catching it, because untreated chlamydia can lead to serious complications over time, including pelvic inflammatory disease, chronic pain, and fertility problems in women, and epididymitis (painful inflammation near the testicle) in men.