Untreated chlamydia causes progressive damage to your reproductive tract through chronic inflammation and scarring, and the longer the infection persists, the greater the risk. About 75% of women and 50% of men with chlamydia have no symptoms at all, which means the infection can quietly do damage for months or even years before anyone catches it.
The core problem is that your immune system keeps fighting the bacteria but can’t fully clear it on its own. That ongoing battle creates inflammation, and over time, inflammation turns into scar tissue. Scarring in the reproductive tract is what drives most of chlamydia’s serious consequences.
How Chlamydia Survives Long-Term
Chlamydia is unusually good at hiding from your immune system. When conditions get hostile, the bacteria enter a dormant-like state where they stop reproducing and become essentially invisible to immune cells. They stay alive but inactive, waiting for conditions to improve before resuming their normal life cycle. This is one reason the infection can linger for so long without being detected or cleared naturally.
Even in this dormant state, the bacteria still provoke a low-grade immune response. Your body’s cells release inflammatory signals, and the tissue around the infection site keeps trying to heal itself. When that healing process is triggered repeatedly over weeks and months, it goes haywire. Cells that normally line the reproductive tract start transforming into scar-producing cells, laying down thick, fibrous tissue where healthy tissue should be. Recent research shows the bacteria can also trigger this scarring process directly, not just through the immune response.
Damage to the Female Reproductive Tract
The most well-documented consequence of long-term chlamydia in women is pelvic inflammatory disease (PID), an infection that spreads from the cervix up into the uterus, fallopian tubes, and surrounding tissue. Within the first year of an untreated chlamydia infection, roughly 1 in 10 women develop PID. Once PID occurs, 15 to 20% of those women go on to develop infertility from scarred, blocked fallopian tubes.
That scarring doesn’t just block eggs from reaching the uterus. It also creates an environment where a fertilized egg can get trapped in the fallopian tube, leading to an ectopic pregnancy. A large prospective study published in The Lancet Regional Health tracked women from 2008 to 2022 and found that women with a history of chlamydia had nearly double the risk of ectopic pregnancy compared to women who tested negative. Their risk of tubal factor infertility was nearly three times higher.
PID itself can range from mild to severe. Some women experience pelvic pain, pain during sex, and abnormal bleeding. Others develop PID with minimal symptoms, only discovering the damage years later when they struggle to conceive. Each episode of PID increases the cumulative scarring, so women who are reinfected with chlamydia face compounding risks.
Consequences for Men
In men, untreated chlamydia most commonly travels from the urethra to the epididymis, the coiled tube behind each testicle where sperm mature. This causes epididymitis: pain, swelling, and tenderness in the scrotum that can become chronic. If the inflammation spreads further, it can involve the testicle itself or the prostate gland.
The same scarring process that damages fallopian tubes in women can obstruct the ducts that carry sperm in men. Scar tissue narrows or blocks the passages, reducing sperm count or preventing sperm from reaching semen at all. Urethral strictures, where scarring narrows the urethra, have also been linked to chronic chlamydial infections. While male infertility from chlamydia is less thoroughly studied than female infertility, the mechanism of inflammatory scarring and obstruction is well established.
Reactive Arthritis
Chlamydia can trigger joint inflammation even in parts of the body far from the infection site. Reactive arthritis typically shows up days to weeks after the initial infection and primarily hits the knees, ankles, sacroiliac joint, and lower spine. It usually affects fewer than six joints at a time and comes on suddenly.
For sexually acquired reactive arthritis, joint symptoms generally appear about two weeks after genital symptoms, though they can develop up to three months later. In some people, especially those with a long-standing untreated infection, the arthritis becomes a chronic, recurring condition rather than a one-time flare.
Risks During Pregnancy and for Newborns
If chlamydia is still present at the time of delivery, the risks extend to the baby. Between 50 and 70% of infants born to mothers with active genital chlamydia will acquire the infection during a vaginal birth if no preventive treatment is given. The two main complications in newborns are eye infection and pneumonia.
Chlamydial conjunctivitis is the most common cause of newborn eye infection in developed countries, appearing in the first weeks of life as redness, swelling, and discharge. Pneumonia from chlamydia is slower to develop, typically showing up around six weeks of age, and affects an estimated 10 to 20% of infected infants. Both are treatable with antibiotics, but they require medical attention and can be serious if missed.
Why Screening Matters
Because most chlamydia infections produce no obvious symptoms, routine testing is the only reliable way to catch it before damage accumulates. The CDC recommends annual screening for all sexually active women under 25, and for older women with risk factors like a new sexual partner or a partner with a known STI. For men, routine screening is recommended primarily in higher-risk settings, such as STI clinics, or for men who have sex with men.
The good news is that chlamydia is easily cured with antibiotics at any stage. Treatment stops the infection and halts further damage. What it cannot do is reverse scarring that has already formed. Scar tissue in the fallopian tubes, epididymis, or urethra is permanent. That gap between “easily curable” and “damage already done” is exactly why long-term untreated chlamydia is so consequential. The earlier it’s caught, the less there is to undo.