Chlamydia spreads through vaginal, anal, or oral sex with someone who has the infection. It passes through direct contact with infected genital fluids, not through casual contact like hugging, sharing drinks, or sitting on toilet seats. With over 1.5 million cases reported in the U.S. in 2024 alone, it remains the most common bacterial sexually transmitted infection in the country.
Sexual Contact Is the Primary Route
The bacterium that causes chlamydia, Chlamydia trachomatis, needs direct contact with mucous membranes to establish an infection. These are the moist, delicate tissues lining the genitals, rectum, and throat. During unprotected vaginal, anal, or oral sex, infected fluids from one person’s body come into contact with these tissues in another person, and the bacteria take hold.
Rectal infections can happen two ways: through receptive anal sex, or by the bacteria spreading from an existing vaginal infection to the rectum on its own. Throat infections are less common but possible through oral sex. You don’t need to have penetrative intercourse to transmit it. Any genital-to-genital or genital-to-mouth contact that involves infected fluids can be enough.
A pregnant person with chlamydia can also pass it to their baby during childbirth, which can cause eye infections or pneumonia in the newborn.
Why People Spread It Without Knowing
The biggest reason chlamydia spreads so effectively is that most people who have it feel completely fine. About 75% of women and 50% of men with chlamydia have no symptoms at all. That means someone can carry and transmit the infection for weeks or months without any clue they’re infected. There’s no way to tell by looking at a partner or by how you feel after sex whether transmission occurred.
When symptoms do appear, they typically show up one to three weeks after exposure. In women, that might look like unusual vaginal discharge, burning during urination, or bleeding between periods. In men, symptoms tend to include discharge from the penis, burning with urination, or pain and swelling in one or both testicles. Rectal infections may cause discharge, pain, or bleeding regardless of sex.
You Can’t Get It From Toilet Seats or Towels
Chlamydia bacteria can technically survive on surfaces like plastic, skin, and cotton cloth for up to 24 hours under laboratory conditions, but only at high concentrations. In real-world scenarios, the amount of bacteria deposited on a toilet seat, towel, or doorknob would be far too low to cause a genital infection. The bacteria need warm, moist mucous membranes to infect, and casual surface contact doesn’t deliver them there in any meaningful quantity.
The one exception involves eye infections. Research on trachoma (a related eye disease caused by the same family of bacteria) has shown that contaminated hands or cloths can transfer bacteria to the eyes. But genital chlamydia from a toilet seat, swimming pool, or shared clothing is not a realistic concern.
Reinfection From Untreated Partners
Getting treated for chlamydia doesn’t protect you from getting it again. If your partner wasn’t treated at the same time, the infection simply passes back the next time you have sex. This “ping-pong” effect is extremely common, especially among younger people. Studies show that nearly one in five teenage women treated for chlamydia are reinfected within two years. About 6% are reinfected within just six months.
Repeat infections aren’t just an inconvenience. Each round of chlamydia increases the risk of serious complications, particularly pelvic inflammatory disease, which can lead to chronic pelvic pain, ectopic pregnancy, and infertility. This is why both partners need to complete treatment and avoid sex until the infection has cleared before resuming sexual activity.
When to Get Tested After Exposure
If you think you were exposed, testing too early can give you a false negative. The standard recommendation is to wait at least one week after the possible exposure before getting tested. Waiting two weeks catches nearly all infections. The most common test is a simple urine sample or a swab of the vagina, rectum, or throat, depending on the type of contact involved.
Because so many infections are silent, routine screening matters even without a known exposure. Sexually active women under 25 and anyone with new or multiple partners benefit from annual testing. A single course of antibiotics clears the infection in most cases, but you’ll want to retest about three months after treatment to make sure you haven’t been reinfected.
What Actually Lowers Your Risk
Condoms used consistently and correctly during vaginal, anal, and oral sex are the most effective way to reduce your risk. They don’t eliminate it entirely, since skin-to-skin contact around areas the condom doesn’t cover can still transmit some infections, but they block the primary fluid-based route chlamydia uses to spread.
Fewer sexual partners and mutual testing before starting a new sexual relationship both lower your odds significantly. If you’re diagnosed, notifying recent partners so they can get tested and treated breaks the chain of transmission and protects you from reinfection down the line.