Untreated chlamydia can lead to serious reproductive damage in both women and men, joint inflammation, increased vulnerability to other infections, and pregnancy complications. Because roughly 75% of women and 50% of men with chlamydia have no symptoms at all, the infection often progresses silently for months before anyone realizes it’s there.
Pelvic Inflammatory Disease in Women
The most common serious consequence of chlamydia in women is pelvic inflammatory disease, or PID. About 10% of women with untreated chlamydia develop PID, an infection that spreads from the cervix into the uterus, fallopian tubes, or ovaries. PID causes lower abdominal pain, fever, unusual discharge, and pain during sex, but it can also be mild enough to go unnoticed while still causing internal damage.
PID matters because of what it leaves behind. The infection triggers inflammation that leads to scar tissue forming inside the fallopian tubes. That scarring can partially or fully block the tubes, which sets the stage for two of the most significant long-term consequences: infertility and ectopic pregnancy.
Fallopian Tube Damage and Infertility
Chlamydia damages the fallopian tubes through a chain reaction involving the immune system. When the body detects the bacteria, it sends inflammatory cells to fight the infection. Those immune cells release proteins that break down normal tissue and trigger fibrosis, essentially replacing healthy, flexible tube lining with stiff scar tissue. The infection also directly destroys the tiny hair-like structures (cilia) that line the inside of the tubes. These cilia are responsible for moving an egg from the ovary toward the uterus, so losing them disrupts fertility even when the tubes aren’t fully blocked.
What makes this damage especially insidious is that it worsens with repeated infections. Each new chlamydia infection reactivates the immune response, and the scarring compounds. A large prospective study published in The Lancet Regional Health found that women who tested positive for chlamydia had a nearly threefold increased risk of tubal factor infertility compared to women who never had the infection. The damage is also permanent. Once scar tissue forms and cilia are destroyed, there’s no way to reverse it with antibiotics or medication.
Ectopic Pregnancy
When scar tissue partially blocks a fallopian tube, a fertilized egg can get stuck there instead of reaching the uterus. This is an ectopic pregnancy, and it’s a medical emergency. The tube can’t support a growing pregnancy, and if it ruptures, it causes life-threatening internal bleeding.
The same Lancet study found that women with a history of chlamydia had an 84% higher risk of ectopic pregnancy than women without. Even a single past infection raises the risk, though repeated infections increase it further.
Effects on Male Reproductive Health
Chlamydia isn’t just a concern for women. In men, the most common complication is epididymitis, an infection of the coiled tube at the back of each testicle that stores and carries sperm. Chlamydia is one of the leading causes of epididymitis in sexually active men under 35. Symptoms include swelling, warmth, and pain in one or both testicles, sometimes severe enough to make walking uncomfortable.
Most cases of epididymitis resolve with antibiotics without lasting harm. In rare cases, though, the infection can reduce fertility by damaging the structures involved in sperm transport or by affecting sperm quality.
Reactive Arthritis
Some people develop joint inflammation weeks after a chlamydia infection, a condition called reactive arthritis. The immune system, primed to fight the bacterial infection, mistakenly attacks the body’s own joint tissue. Typical symptoms include pain and swelling in the knees, ankles, or heels, along with swollen fingers or toes and persistent lower back pain that’s worse at night or first thing in the morning.
Reactive arthritis can also cause red, irritated eyes, burning during urination, and a rash on the palms of the hands or soles of the feet. Most people recover within a few months to a year, though some develop chronic symptoms. It’s worth noting that most people with chlamydia never develop reactive arthritis. It’s an uncommon complication, but one that catches people off guard because they don’t associate joint pain with a genital infection.
Increased Risk of HIV
An active chlamydia infection makes it easier to acquire or transmit HIV. The inflammation chlamydia causes in the genital tract draws more immune cells to the area, and those are precisely the cells HIV targets. The infection also disrupts the mucosal barrier that normally helps block HIV from entering the body. Research published in The Lancet found that chlamydia increased the replication of HIV in co-infected individuals, likely through inflammatory byproducts released by immune cells fighting the chlamydia bacteria.
Lymphogranuloma Venereum
Certain aggressive strains of chlamydia cause a condition called lymphogranuloma venereum, or LGV. This is most commonly seen in men who have sex with men and involves severe inflammation that goes beyond the typical chlamydia infection. When it affects the rectum, LGV causes proctocolitis: painful inflammation with mucous or bloody discharge, constipation, fever, and a constant feeling of needing to use the bathroom. The symptoms can be severe enough to mimic inflammatory bowel disease.
If LGV isn’t treated early, it can lead to chronic scarring, fistulas (abnormal tunnels between the rectum and surrounding tissue), and narrowing of the rectal passage. It can also cause large, painful swollen lymph nodes in the groin that sometimes need to be drained. Even with successful antibiotic treatment, the tissue damage from LGV can leave permanent scarring.
Complications During Pregnancy
Pregnant women with untreated chlamydia can pass the infection to their baby during delivery. This can cause eye infections (neonatal conjunctivitis) and pneumonia in newborns. Chlamydia during pregnancy has also been linked to preterm birth and low birth weight, though the infection itself is easily treated with antibiotics that are safe to use during pregnancy.
Why Screening Matters
The core problem with chlamydia is the gap between infection and symptoms. Three out of four women and half of men feel nothing at all while the bacteria quietly causes damage. By the time symptoms appear, if they ever do, the infection may have already progressed to PID or caused tubal scarring.
The CDC recommends annual chlamydia screening for all sexually active women under 25 and for older women with risk factors like a new partner or multiple partners. For men, routine screening isn’t universally recommended but is advised in high-prevalence settings and for men who have sex with men. More frequent testing may be warranted based on individual risk. Chlamydia is curable with a short course of antibiotics, and early treatment prevents nearly all of the complications described above. The damage it causes is almost entirely a consequence of delayed detection.