Chlamydia is a bacterial infection that invades your cells, triggers inflammation, and, if left untreated, can cause permanent damage to your reproductive system. About 75% of women and 50% of men with chlamydia have no symptoms at all, which means the infection often works silently for weeks or months before anyone realizes it’s there.
How the Bacteria Takes Over Your Cells
Chlamydia doesn’t just sit on the surface of your tissue. It’s an intracellular parasite, meaning it actually gets inside your cells to survive and reproduce. The bacteria has two forms: a tough, spore-like form that travels between people and attaches to new cells, and a softer, replicating form that multiplies once inside. After the bacteria latches onto a cell in your cervix, urethra, rectum, or throat, it enters and essentially hijacks the cell’s resources, stealing nutrients to fuel its own growth.
Because chlamydia’s genome is too small for it to produce everything it needs on its own, it’s completely dependent on your cells. Once inside, the bacteria multiplies until the cell is packed with new infectious particles. These eventually burst out or get released, spreading to neighboring cells and continuing the cycle. This process drives the inflammation and tissue damage that causes problems down the line.
What It Does in Women
In women, chlamydia typically starts in the cervix. When symptoms do appear, they often include a change in vaginal discharge, bleeding between periods, or bleeding after sex. But the real danger is what happens when the infection stays quiet and creeps upward through the reproductive tract.
If untreated, roughly 10 to 15% of women with chlamydia develop pelvic inflammatory disease (PID). PID is an umbrella term for infection and inflammation that spreads to the uterus, fallopian tubes, and surrounding tissue. The inflammation can create scar tissue inside the fallopian tubes, narrowing or blocking them entirely. This scarring is permanent. It can make it difficult or impossible to get pregnant, and it raises the risk of ectopic pregnancy, where a fertilized egg implants outside the uterus, a potentially life-threatening situation.
What makes PID particularly dangerous is that even mild or “silent” cases with no noticeable symptoms can still cause enough internal scarring to affect fertility. Women sometimes don’t learn about the damage until they have trouble conceiving years later.
What It Does in Men
In men, chlamydia usually infects the urethra first. Those who do notice symptoms typically report a discharge from the penis, a burning feeling when urinating, or pain and swelling in one or both testicles. The testicular symptoms point to epididymitis, an inflammation of the tube that stores and carries sperm from the testicle.
Epididymitis from chlamydia can cause fever along with significant scrotal pain. In rare cases, the resulting inflammation and scarring can lead to infertility in men as well, though this is much less common than in women.
Infections Beyond the Genitals
Chlamydia doesn’t only infect the reproductive tract. It can also establish itself in the rectum and the throat, depending on how it was transmitted. Rectal chlamydia may cause pain, discharge, or bleeding, though it’s frequently asymptomatic. Throat infections are also common and nearly always produce no symptoms, which makes them easy to miss without specific testing.
The eyes are another vulnerable site. If the bacteria reaches your eyes through contaminated hands or fluids, it can cause conjunctivitis, a red, painful eye infection with discharge. This is also how newborns can be infected during delivery.
Reactive Arthritis
One of the less well-known effects of chlamydia is reactive arthritis, a condition where your immune system essentially overreacts to the infection and starts attacking your own joints. Even after the bacteria has been treated, fragments of it can end up in joint fluid, triggering an inflammatory immune response. The classic pattern involves joint pain (often in the knees or ankles), eye inflammation, and urinary symptoms all occurring together, though only about a third of people with reactive arthritis experience all three at once.
People who carry a specific genetic marker called HLA-B27 are more susceptible to this complication. The arthritis can become chronic in some cases, with ongoing joint damage linked to an immune response that struggles to fully clear bacterial remnants from the joints.
Risks During Pregnancy
Chlamydia during pregnancy creates risks for both the mother and the baby. An untreated infection can be passed to the newborn during vaginal delivery. The two main conditions that develop in exposed newborns are chlamydial conjunctivitis, an eye infection that appears in the first few weeks of life, and chlamydial pneumonia, a lung infection that can develop in the first few months. Both are treatable but avoidable with screening and treatment before delivery.
For the mother, an active infection also increases the risk of postpartum complications. This is why screening is recommended during pregnancy, and retesting in the third trimester helps catch any new infections before delivery.
Treatment and Recovery Timeline
The infection itself clears relatively quickly with antibiotics. You’re typically advised to avoid sex for seven days after treatment to prevent passing the bacteria to a partner. If symptoms were present, they usually resolve within that same window, though inflammation may take a bit longer to fully settle.
Retesting is recommended about three months after treatment, regardless of whether your partner was also treated. This isn’t to check whether the antibiotic worked (it almost always does) but to catch reinfection, which is common. Reinfection matters because each round of chlamydia gives the bacteria another opportunity to cause the kind of scarring and inflammatory damage described above. The infection itself is easy to cure. The tissue damage it leaves behind is not.