You get chlamydia through vaginal, anal, or oral sex with someone who has the infection. Ejaculation does not need to happen for the bacteria to spread. Chlamydia is one of the most common sexually transmitted infections worldwide, and most people who have it don’t know because it rarely causes obvious symptoms.
How Chlamydia Spreads
Chlamydia is caused by the bacterium Chlamydia trachomatis, which lives in genital secretions. It passes from one person to another through direct contact with infected tissue during sex. The three main routes are vaginal intercourse, anal intercourse, and oral sex. Any of these can transmit the infection even without a condom breaking or any visible signs of infection in either partner.
The infection can also spread between body sites. Someone with a vaginal chlamydia infection can develop a rectal infection through spread from the vagina, not only through anal sex. This means testing at a single site can sometimes miss an active infection elsewhere.
Pregnant women with chlamydia can pass it to their baby during vaginal delivery, which can cause eye infections or pneumonia in the newborn. This is one reason prenatal screening is routine.
Chlamydia does not spread through casual contact like hugging, sharing food, or using the same toilet seat. It requires direct mucous membrane contact during sexual activity.
Why Most People Don’t Know They Have It
About 75% of women and 50% of men with chlamydia have no symptoms at all. This is the main reason the infection spreads so easily: people unknowingly pass it to sexual partners because they feel perfectly fine.
When symptoms do appear, they typically show up one to three weeks after exposure. In women, this can look like unusual vaginal discharge, burning during urination, or bleeding between periods. In men, the most common signs are a clear or cloudy discharge from the penis, burning while urinating, or pain and swelling in one or both testicles. Rectal infections may cause discharge, pain, or bleeding from the rectum, though they’re often silent too.
Because symptoms are unreliable, the only way to know your status is through testing. Sexually active people under 25 and anyone with a new partner or multiple partners benefit from regular screening.
How Testing Works
Chlamydia is diagnosed with a simple test called a nucleic acid amplification test, which detects the bacteria’s genetic material. These tests are over 90% sensitive and more than 99% specific, meaning false results are uncommon.
For women, the most accurate option is a vaginal swab, which can be self-collected. A urine sample also works but may miss up to 10% of infections compared to a swab. For men, a urine sample performs just as well as a urethral swab, and in some cases better. If you’ve had anal or oral sex, your provider may recommend swabs from the throat or rectum, since a standard urine test won’t detect infections at those sites.
Results typically come back within a few days. Many clinics and online services now offer at-home collection kits that you mail to a lab.
Treatment and Follow-Up
Chlamydia is curable with antibiotics. The standard treatment is a seven-day course of doxycycline taken twice daily. A single-dose alternative exists for people who may have difficulty completing the full week. Both are highly effective when taken as directed.
You should avoid sex for seven days after completing treatment (or seven days after a single-dose antibiotic) to prevent passing the infection to a partner. Any recent sexual partners need to be notified and treated as well, even if they have no symptoms. Otherwise, you can easily become reinfected.
Retesting is recommended three months after treatment. This isn’t because the antibiotics failed. It’s because reinfection from an untreated partner or a new exposure is common. Getting retested catches a repeat infection early before it causes complications or spreads further.
What Happens If It Goes Untreated
Left alone, chlamydia doesn’t resolve on its own and can cause serious damage over time. In women, the bacteria can travel up from the cervix into the uterus and fallopian tubes, causing pelvic inflammatory disease. PID can lead to chronic pelvic pain, scarring of the fallopian tubes, difficulty getting pregnant, and a higher risk of ectopic pregnancy, where a fertilized egg implants outside the uterus.
In men, untreated chlamydia can cause epididymitis, a painful infection in the tube that carries sperm from the testicle. In rare cases, this leads to infertility. Both men and women can develop reactive arthritis, a condition involving swollen joints and eye inflammation that can persist even after the infection itself is treated.
These complications are largely preventable with early detection and a simple course of antibiotics, which is why routine screening matters so much for a disease that usually causes no warning signs.
Reducing Your Risk
Latex condoms, used consistently and correctly, reduce the risk of chlamydia transmission by acting as a physical barrier to the genital secretions that carry the bacteria. They aren’t 100% effective, since chlamydia can infect areas a condom doesn’t fully cover, but they significantly lower the odds.
Other practical steps include limiting the number of sexual partners, getting screened regularly, and making sure both you and a new partner are tested before having unprotected sex. If you’re diagnosed, completing treatment and notifying partners breaks the chain of transmission and protects both your health and theirs.