Yes, chlamydia is a sexually transmitted infection (STI) caused by the bacterium Chlamydia trachomatis. It spreads primarily through vaginal, anal, and oral sex, and it is both the most commonly reported bacterial STI in the United States and one of the most treatable. In 2024, over 1.5 million cases were reported to the CDC.
How Chlamydia Spreads
Chlamydia passes from person to person during unprotected vaginal, anal, or oral sex. You don’t need to have penetrative sex to transmit it; any contact with infected genital fluids or mucous membranes can be enough. The infection can also establish itself in the rectum, either through anal sex or by spreading from the vagina.
A pregnant person with chlamydia can pass the infection to their baby during delivery, which can cause eye infections or pneumonia in the newborn. Outside of sexual contact and childbirth, chlamydia does not spread through casual contact like hugging, sharing food, or using the same toilet.
Why Most People Don’t Know They Have It
Chlamydia is often called a “silent” infection because the majority of people who contract it never develop noticeable symptoms. This is a major reason it spreads so easily. People can carry and transmit the bacteria for weeks or months without realizing anything is wrong.
When symptoms do appear, they typically show up one to three weeks after exposure. In women, signs can include unusual vaginal discharge, burning during urination, and bleeding between periods. In men, symptoms tend to involve discharge from the penis, burning with urination, and occasionally pain or swelling in the testicles. Rectal infections may cause pain, discharge, or bleeding regardless of sex.
What Happens if It Goes Untreated
Because chlamydia so often flies under the radar, untreated infections can quietly cause damage over time, particularly in the reproductive system. A long-term study following women from 2008 to 2022 found that those who tested positive for chlamydia had significantly higher risks of pelvic inflammatory disease (PID), ectopic pregnancy, and tubal factor infertility compared to women who tested negative. Specifically, the risk of PID was about 1.6 times higher, ectopic pregnancy nearly twice as likely, and tubal infertility almost three times more common.
An important nuance from that research: symptomatic chlamydia infections carried a much stronger link to PID than asymptomatic ones. Women with symptomatic infections had roughly 2.3 times the risk of developing PID, while asymptomatic infections showed no statistically significant increase. That said, the overall incidence of these complications remained low even among those with symptomatic infections, with fewer than 6 cases of PID per 1,000 person-years.
In men, untreated chlamydia can lead to infection of the tube that carries sperm, causing pain and, in rare cases, affecting fertility. For both sexes, having chlamydia also makes it easier to contract or transmit HIV.
How It’s Diagnosed
Testing for chlamydia is simple and painless. The gold standard is a nucleic acid amplification test (NAAT), which detects the bacterium’s genetic material and is highly accurate. For women, the preferred sample is a vaginal swab, which you can collect yourself. For men, a urine sample works just as well as a swab. If you’ve had oral or anal sex, your provider can test throat or rectal samples too.
Results typically come back within a few days. Many clinics, health departments, and even mail-order kits now offer chlamydia testing, making it more accessible than ever.
Treatment Is Quick and Effective
Chlamydia is curable with a short course of antibiotics. The standard treatment for most adults is a seven-day oral antibiotic regimen. During pregnancy, a single-dose alternative is used instead. In either case, the infection clears completely with proper treatment.
You should avoid sex for at least seven days after completing treatment (or seven days after a single-dose option) to prevent passing the infection to a partner. Your provider will likely recommend retesting about three months later, because reinfection is common, especially if a sexual partner wasn’t treated at the same time.
Who Should Get Screened
Because chlamydia so frequently produces no symptoms, routine screening is the most reliable way to catch it. The CDC recommends annual chlamydia screening for all sexually active women under 25. Women 25 and older should be screened if they have risk factors like a new partner, multiple partners, a partner with an STI, or inconsistent condom use.
For men who have sex with men, the recommendation is at least annual screening at all sites of sexual contact, with testing every three to six months for those at higher risk, such as those on HIV prevention medication or with multiple partners. For heterosexual men at low risk, routine screening isn’t strongly recommended, though it may be offered in high-prevalence settings like STI clinics or correctional facilities.
Transgender and gender-diverse individuals should follow screening guidelines based on their anatomy. Anyone with a cervix who is sexually active and under 25 should be screened annually, regardless of gender identity. Pregnant people under 25 should be tested early in pregnancy and again in the third trimester, with a follow-up test four weeks after treatment if the initial result is positive.
Reducing Your Risk
Consistent condom use during vaginal, anal, and oral sex significantly reduces the chance of transmission, though it doesn’t eliminate risk entirely since chlamydia can infect areas a condom doesn’t cover. Being in a mutually monogamous relationship with a partner who has tested negative is the most reliable form of prevention outside of abstinence. Regular screening, especially if you have new or multiple partners, catches infections early and prevents both complications and further spread.