Chlamydia spreads through sexual contact, primarily when infected genital, rectal, or throat fluids come into contact with a partner’s mucous membranes. It does not require ejaculation to transfer. Any unprotected vaginal, anal, or oral sex with an infected person can pass the bacteria, and most people who have it don’t know they’re carrying it.
Sexual Contact Is the Primary Route
The bacterium that causes chlamydia thrives in the warm, moist cells lining the genitals, rectum, and throat. During unprotected sex, the bacteria transfer through direct contact between these tissues and through infected fluids like vaginal secretions and pre-ejaculate. Penetrative sex isn’t the only risk. Oral sex can transmit chlamydia to or from the throat, though throat infections are less common than genital ones.
Vaginal sex is the most frequent route of transmission. Anal sex, particularly receptive anal sex, carries a high risk of rectal infection. Sharing sex toys that haven’t been cleaned or covered with a new condom between uses can also pass the bacteria from one person to another.
It Can Spread Between Body Sites
Chlamydia doesn’t always stay where it first took hold. Women can develop a rectal infection even without having anal sex, because infected vaginal secretions can carry the bacteria to the rectum on their own. This kind of site-to-site spread is well documented and explains why screening sometimes catches infections in locations a person wouldn’t expect.
The bacteria can also reach the eyes. If you touch infected genital or rectal fluids and then touch your eyes, you can transfer chlamydia to the conjunctiva, the thin membrane covering the eye. This is called auto-inoculation, and it can cause a form of conjunctivitis that requires treatment. It’s uncommon, but it happens, and it’s one reason handwashing matters during and after sexual activity.
Why Most People Don’t Know They Have It
About 75% of women and 50% of men with chlamydia experience no symptoms at all. This is the single biggest factor driving transmission. People who feel perfectly healthy continue having unprotected sex without knowing they’re infectious, sometimes for weeks or months. The infection is fully capable of spreading during this silent phase.
When symptoms do appear, they typically show up one to three weeks after exposure. In women, that might mean unusual vaginal discharge or a burning sensation when urinating. In men, it often looks like discharge from the penis or mild testicular discomfort. But because so many cases are symptom-free, routine screening is the only reliable way to catch it early.
Transmission During Childbirth
A pregnant person with an untreated chlamydia infection can pass the bacteria to their baby during vaginal delivery. As the infant moves through the birth canal, the bacteria can infect the baby’s eyes, causing neonatal conjunctivitis, or reach the lungs, potentially leading to pneumonia in the first few months of life. In rare cases, the infection can also travel upward before delivery through the amniotic membranes. This is why prenatal screening for chlamydia is standard practice.
What Doesn’t Spread Chlamydia
Casual contact does not transmit chlamydia. You won’t get it from hugging, sharing food, sitting on a toilet seat, or swimming in a pool. The bacteria need direct contact with mucous membrane tissue to establish an infection, and they don’t survive well in the open environment.
That said, lab studies have found that chlamydia bacteria can remain viable on surfaces like plastic, skin, and cotton fabric for up to 24 hours under controlled conditions. The bacterial load drops steadily, losing roughly 25 to 30% of viable organisms per hour depending on the surface. In real-world settings, the amount of bacteria on a shared towel or surface would almost certainly be too low to cause infection. Researchers studying this were focused on eye-to-eye transmission in areas with endemic trachoma (an eye disease caused by a related strain), not typical sexual health scenarios. For practical purposes, surface contact is not considered a meaningful risk for genital chlamydia.
Reinfection After Treatment
Chlamydia is curable with antibiotics, but being treated once does not make you immune. You can catch it again immediately if you have unprotected sex with an infected partner. This is a common pattern: one partner gets treated, the other doesn’t get tested, and the bacteria pass right back. Both partners need to be treated before resuming sexual contact, and most guidelines recommend waiting at least seven days after completing treatment before having sex again.
Reinfection rates are high enough that retesting about three months after treatment is recommended, regardless of whether your partner was also treated. Repeated infections increase the risk of complications, particularly pelvic inflammatory disease in women, which can affect fertility.