Chlamydia is the most commonly reported bacterial sexually transmitted infection in the United States, and while it’s easily curable with antibiotics, leaving it untreated can cause serious damage. The real danger isn’t the infection itself, which often produces no symptoms at all, but what happens when it silently spreads deeper into the reproductive system over weeks or months.
Most People Don’t Know They Have It
About 75% of women and 50% of men with chlamydia have no symptoms whatsoever. That’s what makes this infection so deceptive. You can carry it for months, pass it to partners, and develop complications without ever feeling sick. When symptoms do appear, they’re often mild: unusual discharge, burning during urination, or light bleeding between periods. These are easy to dismiss or mistake for something else.
This silent nature is why routine screening matters. The U.S. Preventive Services Task Force recommends chlamydia screening for all sexually active women age 24 and younger, and for older women with risk factors like new or multiple sexual partners. There’s no firm consensus on how often to screen, but annual testing is a common benchmark for anyone sexually active.
What Happens If It Goes Untreated in Women
Untreated chlamydia in women can climb from the cervix into the uterus and fallopian tubes, triggering pelvic inflammatory disease (PID). A large evidence synthesis estimated that roughly 17% of women with untreated chlamydia will develop PID, including cases that are never formally diagnosed. That’s nearly 1 in 5.
PID is where the real consequences stack up. Inflammation scars the fallopian tubes, which can block eggs from reaching the uterus. In a major clinical study tracking over 800 women with PID for about three years, 18% reported infertility and 29% experienced some degree of chronic pelvic pain. Scarred tubes also raise the risk of ectopic pregnancy, where a fertilized egg implants outside the uterus, a potentially life-threatening emergency.
The frustrating part is that even mild, barely noticeable PID can cause this kind of damage. You don’t need a dramatic infection to end up with scarring that affects your fertility years later.
Risks for Men
Chlamydia in men most commonly causes urethritis, an inflammation of the tube that carries urine. Left alone, it can spread to the epididymis, the coiled tube behind each testicle where sperm matures. Chlamydia is responsible for an estimated 40 to 80% of epididymitis cases in younger men. The infection causes swelling, pain, and sometimes fever.
Repeated or severe epididymitis can damage the tubes that transport sperm, potentially leading to testicular atrophy and obstructive azoospermia, a condition where sperm can’t get out. While male infertility from chlamydia is less studied than female infertility, the mechanism is clear: chronic inflammation scars the reproductive plumbing.
Serious Risks During Pregnancy
Chlamydia during pregnancy raises the stakes considerably. The infection has been linked to premature rupture of membranes, preterm labor, low birth weight, and pregnancy loss. Without treatment, the vertical transmission rate to newborns during delivery can be as high as 50 to 70%.
Babies born to mothers with active chlamydia face two main complications. An estimated 30 to 50% of exposed newborns develop conjunctivitis, an eye infection that can cause serious damage if untreated. Another 10 to 20% develop pneumonia. Both are treatable, but both are entirely preventable with screening and treatment before delivery.
A Rarer, More Aggressive Form
Not all chlamydia strains behave the same way. Certain strains cause lymphogranuloma venereum (LGV), a more invasive form that penetrates deeper into tissue. LGV can cause painful, swollen lymph nodes in the groin that sometimes form large, pus-filled masses called buboes. When transmitted through rectal contact, it causes proctocolitis, a severe inflammation of the rectum with bloody discharge, intense pain, fever, and ulceration that can mimic inflammatory bowel disease.
If LGV isn’t treated early, it can lead to chronic complications including rectal fistulas, strictures, and reactive arthritis. LGV is most frequently reported among men who have sex with men, but it can affect anyone. It requires a longer course of antibiotics than standard chlamydia.
Treatment Is Straightforward
Standard chlamydia responds well to a week-long course of doxycycline. For rectal infections, a randomized trial found doxycycline achieved a 100% cure rate, compared to 74% for the single-dose alternative. For genital infections in women, both options remain effective, but doxycycline has become the preferred first-line treatment because it covers rectal infections that may coexist without the person knowing.
The catch is that antibiotics can kill the bacteria but can’t reverse damage already done. Scarred fallopian tubes stay scarred. A blocked epididymis stays blocked. This is why timing matters so much. The difference between a chlamydia infection that’s a minor inconvenience and one that changes your reproductive future often comes down to how quickly it’s caught.
The Bottom Line on Severity
Chlamydia sits in an unusual spot among infections. Treated promptly, it’s one of the least consequential STIs you can get: a short course of pills and it’s gone. But its ability to hide without symptoms means many people don’t get treated promptly, and that’s where the damage accumulates. Nearly 1 in 5 untreated women develop pelvic inflammatory disease. Men risk losing fertility through damaged reproductive tubes. Pregnant women risk passing a preventable infection to their babies. The infection itself isn’t dangerous. The silence is.