Chlamydia spreads through vaginal, anal, or oral sex with someone who has the infection. It passes through contact with infected genital fluids, not through casual touch, and it’s one of the most common sexually transmitted infections in the world. What makes chlamydia particularly easy to catch is that most people who have it don’t know it: about 75% of women and 50% of men with chlamydia have no symptoms at all, meaning they can pass it along without realizing anything is wrong.
Vaginal and Anal Sex
The most common way chlamydia spreads is through unprotected vaginal or anal intercourse. The bacteria live in infected genital fluids, including semen and vaginal secretions, and transfer during skin-to-mucous-membrane contact. You don’t need to have a large number of sexual partners to be at risk. A single encounter with an infected person is enough.
Chlamydia can also infect the rectum. This happens through receptive anal sex, but it can also spread from an existing vaginal infection to the rectum without anal sex being involved. Rectal chlamydia often produces no symptoms, which means it can go undetected and be passed to future partners.
Oral Sex
Chlamydia can infect the throat through oral sex performed on someone with a genital or rectal infection. The reverse is also possible: if someone has chlamydia in their throat, they can transmit it to a partner’s genitals during oral sex. Throat infections tend to cause fewer problems than genital ones, but they still matter because they serve as a hidden source of ongoing transmission. Many people don’t think of oral sex as a risk for chlamydia, so throat infections rarely get tested for or treated.
Spread to the Eyes
Chlamydia can infect the eyes if contaminated genital fluid reaches them, typically through your hands. Touching your genitals or a partner’s genitals and then rubbing your eyes is the most straightforward route. This type of eye infection, called inclusion conjunctivitis, is caused by the same strains of chlamydia that cause genital infections. It produces redness, discharge, and irritation that can mimic pink eye. The global rise in genital chlamydia has led to a corresponding increase in these eye infections.
From Mother to Baby During Birth
A pregnant woman with chlamydia can pass the infection to her baby during vaginal delivery. This can cause conjunctivitis in the newborn or, in some cases, a respiratory infection. Beyond the direct risk to the baby, chlamydia during pregnancy is linked to complications for the pregnancy itself. One study found that untreated chlamydia more than quadrupled the odds of delivering before 32 weeks. Roughly 15% of very early preterm deliveries in the study population were attributable to chlamydia. This is why routine screening during prenatal care catches and treats infections before delivery.
Ways You Cannot Get Chlamydia
Chlamydia bacteria cannot survive outside the human body for more than a very short time. They need the warm, moist environment of mucous membranes (like those in the cervix, urethra, rectum, or throat) to stay alive. That means you cannot get chlamydia from toilet seats, shared towels, swimming pools, hot tubs, or doorknobs. Even if a droplet of infected fluid landed on a surface, the bacteria would need to reach suitable tissue while still viable, which is extraordinarily unlikely in real-world conditions. Chlorine in pools and hot tubs would kill the bacteria, and the dilution alone makes waterborne transmission impossible.
You also can’t get chlamydia from hugging, kissing, sharing food or drinks, or being near someone who coughs or sneezes. It requires direct sexual contact or direct transfer of infected fluids to vulnerable tissue.
Why Asymptomatic Spread Is So Common
The reason chlamydia is so widespread comes down to one thing: most infected people feel completely fine. When three out of four women and half of men have zero symptoms, the infection circulates through sexual networks undetected. People don’t get tested because nothing seems wrong, and they unknowingly pass it to new partners. This is why regular screening matters far more for chlamydia than for infections that announce themselves with obvious symptoms.
Symptoms, when they do appear, typically show up one to three weeks after exposure. But the absence of symptoms at that point doesn’t mean you’re in the clear. Many people remain symptom-free for months or even years while still carrying an active, transmissible infection.
Reinfection From Untreated Partners
Getting treated for chlamydia doesn’t protect you if your partner still has it. When partners aren’t treated, the probability of reinfection is about 19%, essentially a one-in-five chance of catching it right back. This “ping-pong” pattern, where the infection bounces between partners, is one of the most common reasons people test positive again shortly after treatment.
When partners are treated quickly (within a few days of the initial diagnosis), reinfection rates drop to around 4%. That difference is dramatic and highlights why partner notification is a standard part of chlamydia treatment. Both people need antibiotics, and both need to avoid sex until treatment is complete, or the cycle simply restarts.
Testing Timeline After Exposure
If you think you’ve been exposed, testing too early can produce a false negative. Chlamydia tests are reliable starting about one week after exposure and catch nearly all infections by two weeks. If you test before that window, the bacterial load may not be high enough to detect. A negative result at one week is reassuring but worth repeating at two weeks if your risk was significant. Testing is simple, usually a urine sample or a swab, and results typically come back within a few days.