Chlamydia is a bacterial infection spread through sexual contact, and it’s the most common bacterial sexually transmitted infection in the world. An estimated 128.5 million new cases occurred globally in 2020 alone. It’s caused by a tiny bacterium called Chlamydia trachomatis that can only survive inside human cells, which is part of why it’s so good at hiding in the body without causing obvious problems.
How You Get Chlamydia
Chlamydia spreads through vaginal, anal, or oral sex without a condom with someone who has the infection. The bacterium lives in genital secretions, so any unprotected sexual contact that involves these fluids can transmit it. You don’t need to have penetrative sex to be at risk; oral sex can also pass the infection, though it’s less common through that route.
The infection can show up in more than one place at once. It can infect the cervix, urethra, rectum, or throat depending on the type of sexual contact. Rectal infections can happen through receptive anal sex or by spreading from another infected site, like the vagina. A pregnant woman with chlamydia can also pass the infection to her baby during childbirth.
You cannot get chlamydia from toilet seats, swimming pools, sharing food, or casual contact like hugging. It requires direct contact with infected genital secretions.
Why Most People Don’t Know They Have It
The most important thing to understand about chlamydia is that it usually causes no symptoms at all. About 75% of women and 50% of men with the infection never notice anything wrong. This is why chlamydia is sometimes called a “silent” infection, and it’s the main reason it spreads so easily. People pass it to partners without ever realizing they’re infected.
When symptoms do appear, they typically show up one to three weeks after exposure, though they can take longer. In women, symptoms may include unusual vaginal discharge, burning during urination, or bleeding between periods. In men, the most common signs are discharge from the penis, burning when urinating, or pain and swelling in one or both testicles. Rectal infections can cause discharge, pain, or bleeding, but often produce no symptoms at all.
What Happens If It Goes Untreated
Because chlamydia so often flies under the radar, it can quietly damage reproductive organs over months or years. In women, about 10 to 15% of untreated infections lead to pelvic inflammatory disease (PID), a serious infection of the uterus, fallopian tubes, and surrounding tissue. PID can cause chronic pelvic pain and scarring that blocks the fallopian tubes, leading to infertility or increasing the risk of ectopic pregnancy, where a fertilized egg implants outside the uterus.
What makes this especially concerning is that chlamydia can cause fallopian tube infection without any symptoms whatsoever. A woman may have no pain, no fever, no sign that anything is wrong, while the infection is silently damaging her fertility. By the time the damage is discovered, it may be permanent.
In men, untreated chlamydia can spread to the tube that carries sperm from the testicle, causing pain, swelling, and in rare cases, fertility problems. For both sexes, having chlamydia also makes it easier to contract or transmit HIV.
How Chlamydia Is Diagnosed
Testing for chlamydia is simple and noninvasive. The gold standard is a type of lab test called a nucleic acid amplification test, which detects the bacterium’s genetic material with high accuracy. For women, a vaginal swab is the preferred sample. Self-collected vaginal swabs are just as accurate as those collected by a clinician, which means many testing sites let you collect your own sample privately. For men, a urine sample works as well as or better than a urethral swab.
If you’ve had oral or anal sex, testing those specific sites matters. Throat and rectal infections won’t show up on a genital test. The same type of test is recommended for rectal and throat samples. Testing is widely available through clinics, doctors’ offices, and sexual health centers, and many areas offer free or low-cost screening.
Because the infection is so often silent, routine screening is recommended for sexually active women under 25 and for anyone with new or multiple sexual partners.
Treatment and Recovery
Chlamydia is fully curable with antibiotics. The recommended treatment for most people is doxycycline, taken as a short course over seven days. It’s a straightforward treatment, and the infection clears in the vast majority of cases. You should avoid sexual contact during the treatment period to prevent passing the infection to a partner.
Both you and your sexual partner (or partners) need to be treated at the same time. If your partner isn’t treated, they’ll simply pass the infection back to you. This is one of the most common reasons people get chlamydia more than once. Reinfection is common and carries the same risks of complications as the original infection, so getting your partner treated isn’t optional.
Having chlamydia once doesn’t give you any immunity. You can be reinfected every time you’re exposed, which is why retesting about three months after treatment is recommended.
How to Protect Yourself
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 bacterium. They aren’t perfect, since skin-to-skin contact outside the area covered by the condom can still transmit some infections, but they are one of the most effective tools available for prevention.
Beyond condoms, reducing your number of sexual partners lowers your overall exposure risk. Having an open conversation with a new partner about testing before sex is practical and increasingly normal. Regular screening is the other key piece of the puzzle, especially given how often chlamydia produces no symptoms. Catching and treating it early prevents both complications and further spread. The global prevalence sits at about 4% for women and 2.5% for men aged 15 to 49, which means it’s common enough that routine testing is a reasonable part of sexual health care for anyone who is sexually active.