Chlamydia spreads through vaginal, anal, or oral sex with someone who has the infection. It does not require ejaculation to transmit. Because up to 75% of infected women and 50% of infected men have no symptoms at all, many people pass it along without realizing they carry it.
Vaginal and Anal Sex Are the Most Common Routes
The bacteria that cause chlamydia, called Chlamydia trachomatis, infect the mucous membranes of the body, particularly the cervix, urethra, and rectum. During unprotected vaginal or anal sex, the bacteria transfer through direct contact with these tissues. You can get a rectal infection either through receptive anal sex or through the bacteria spreading from a nearby infected site, like the vagina. This internal spread, sometimes called auto-inoculation, means a single infection can show up in more than one location in your body.
The infection doesn’t announce itself in most cases. Without testing, many people carry chlamydia for weeks or months, continuing to transmit it to partners. This is the main reason it remains one of the most commonly reported sexually transmitted infections in the United States, with chlamydia contributing to more than 2.2 million combined STI cases reported in 2024 (alongside gonorrhea and syphilis).
Oral Sex Carries a Lower but Real Risk
Chlamydia can infect the throat through oral sex, though this happens less frequently than genital or rectal infection. The clinical significance of throat chlamydia is still somewhat unclear, and routine screening for it isn’t standard practice. However, a chlamydia infection in the throat can be sexually transmitted to a partner’s genitals, so it’s not harmless. If you’re receiving unprotected oral sex from someone with a throat infection, or giving oral sex to someone with a genital infection, transmission is possible in both directions.
Eye Infections From Touch
Chlamydia can infect the eye if you touch infected genital fluids and then touch your eye. This is the same auto-inoculation mechanism that lets the bacteria move between body sites. It’s uncommon, but it happens. The result is a form of conjunctivitis (pink eye) that requires specific antibiotic treatment. Washing your hands after sexual contact is a simple way to avoid this.
Mothers Can Pass It During Childbirth
A pregnant woman with an active chlamydia infection can transmit the bacteria to her baby during vaginal delivery. In one study, roughly half of infants born vaginally to infected mothers tested positive for the bacteria. Even cesarean delivery doesn’t eliminate the risk entirely, particularly if the membranes have already ruptured.
In newborns, chlamydia typically causes eye infection (conjunctivitis) or pneumonia. The pneumonia usually appears one to three months after birth, with rapid breathing and a distinctive staccato cough without fever. Fewer than 10% of babies born to mothers with active chlamydia during labor develop chlamydia pneumonia, but the bacteria are estimated to cause around 12,000 cases of newborn pneumonia per year in the U.S. This is why prenatal screening for chlamydia is routine.
Ways You Cannot Get Chlamydia
Chlamydia bacteria need warm, moist human tissue to survive. They cannot live on dry surfaces. You will not get chlamydia from toilet seats, bath towels, bed linens, swimming pools, or hot tubs. Even if a droplet of infected fluid landed on a surface and hadn’t dried out, the bacteria would need to reach specific tissue like the cervix, urethra, or cornea to cause an infection. Casual skin contact with a contaminated surface doesn’t meet that threshold. Chlorine in pools and hot tubs further eliminates any theoretical risk.
You also cannot get chlamydia from hugging, kissing, sharing food, or being near someone who coughs or sneezes. It is a sexually transmitted infection, not a respiratory or casual-contact one.
Why So Many People Don’t Know They Have It
The single biggest factor driving chlamydia transmission is that most infections produce no noticeable symptoms. Three out of four women and half of men with chlamydia feel completely fine. When symptoms do appear, they typically show up one to three weeks after exposure and can include unusual discharge, burning during urination, or rectal pain. But the absence of symptoms doesn’t mean the infection is harmless. Left untreated, chlamydia can cause pelvic inflammatory disease in women, which can lead to chronic pain and fertility problems. In men, untreated infection can cause painful swelling in the tube that carries sperm.
When to Get Tested After Exposure
If you think you’ve been exposed, testing too early can produce a false negative. Chlamydia testing (usually a urine sample or swab) is reliable about one week after exposure in most cases. Waiting two weeks catches nearly all infections. If you test negative at one week but still have concerns, a follow-up test at two weeks provides strong reassurance.
How Condoms Reduce the Risk
Consistent condom use significantly lowers your chances of getting chlamydia, though it doesn’t eliminate the risk entirely. A study published in the American Journal of Epidemiology found that people who used condoms consistently had a 58% lower rate of chlamydia and gonorrhea compared to those who didn’t, after accounting for other behavioral and demographic factors. The gap between 58% and 100% reflects the reality that condoms don’t cover all genital skin, that they’re sometimes used inconsistently, and that chlamydia can infect sites like the throat and rectum where condom use is less common. Still, condoms remain one of the most effective and accessible tools for reducing transmission alongside regular screening.