Chlamydia is a bacterial infection that, left untreated, can damage your reproductive organs, trigger joint inflammation, and spread to your eyes and throat. What makes it especially dangerous is that most people never realize they have it: roughly 75% of women and 50% of men with chlamydia show no symptoms at all. That means the infection can quietly cause harm for weeks or months before anyone catches it.
How Chlamydia Infects Your Cells
Chlamydia trachomatis is an unusual bacterium because it can only survive inside your cells. It cannot replicate on its own the way most bacteria do. The infection begins when tiny, dormant bacterial particles (only about 250 nanometers wide) latch onto cells lining your genitals, rectum, or throat. These particles hijack your cell’s internal scaffolding to push their way inside, where they create a protective bubble called an inclusion.
Once safely inside that bubble, the bacteria shift into an active, replicating form. They multiply over a cycle that lasts roughly 48 to 96 hours, then convert back into their dormant, infectious form. At the end of the cycle, the new bacteria either burst out of the cell or slip out without destroying it, ready to infect neighboring tissue. This constant cycle of invasion and cell damage is what drives the inflammation and scarring that lead to chlamydia’s worst complications.
What Symptoms Look Like (When They Appear)
When symptoms do show up, they typically take several weeks after exposure. In women, the most common signs are unusual vaginal discharge, burning during urination, and bleeding between periods. In men, symptoms usually involve a watery or milky discharge from the penis, burning when urinating, and sometimes pain or swelling in one or both testicles.
Chlamydia can also infect the rectum, causing discharge, pain, and bleeding, and the throat, where it rarely causes noticeable symptoms. Eye infections are possible too, usually from touching your eye after contact with infected fluids, and can cause redness, discharge, and swelling of the eyelid lining.
Because symptoms are absent in the majority of cases, regular screening is the only reliable way to catch the infection early. The CDC recommends yearly testing for all sexually active women under 25, women 25 and older with risk factors, and sexually active gay and bisexual men.
Damage to the Female Reproductive System
The most serious consequence of untreated chlamydia in women is pelvic inflammatory disease (PID), an infection that spreads from the cervix up into the uterus, fallopian tubes, and surrounding tissue. About 10 to 15% of women with untreated chlamydia will develop PID. The infection doesn’t need to cause obvious symptoms to do this. “Silent” infections in the upper reproductive tract can cause permanent scarring without any pain or fever.
That scarring is the real problem. When scar tissue forms inside the fallopian tubes, it can partially or completely block them. This makes it difficult or impossible for an egg to reach the uterus, leading to infertility. It also raises the risk of ectopic pregnancy, where a fertilized egg implants in the fallopian tube instead of the uterus. Ectopic pregnancies are medical emergencies that can be life-threatening if not treated quickly.
Each repeat infection increases the cumulative damage. Scar tissue builds on scar tissue, so someone who gets chlamydia two or three times faces a significantly higher risk of fertility problems than someone who had it once.
Damage to the Male Reproductive System
In men, the primary complication is epididymitis, an infection of the coiled tube behind each testicle that stores and carries sperm. Chlamydia is one of the most common causes in sexually active men under 35. Symptoms include pain and swelling on one side of the scrotum, sometimes accompanied by fever.
Most cases clear up with antibiotics, but untreated or repeated infections can lead to chronic pain and, in some cases, reduced fertility. The inflammation can damage the delicate tissue of the epididymis enough to impair sperm transport or quality.
Complications Beyond the Reproductive System
Chlamydia can trigger a condition called reactive arthritis, where the immune system’s response to the infection causes painful swelling in joints, typically the knees, ankles, and feet. This can develop weeks after the initial infection and sometimes affects people who never noticed genital symptoms in the first place. It most commonly strikes adults between the ages of 20 and 40. Along with joint pain, reactive arthritis can cause eye inflammation and urinary symptoms, creating a cluster of problems that may persist for months.
There is no single test that confirms reactive arthritis. Diagnosis is based on the combination of a recent infection, characteristic joint symptoms, and lab work that rules out other causes like gout. The joint fluid itself shows high white blood cell counts but no active bacteria, because the inflammation is driven by the immune response rather than the bacteria directly invading the joint.
How Chlamydia Is Treated
Chlamydia is fully curable with antibiotics. The standard treatment is a seven-day course of doxycycline, taken twice daily. A once-daily delayed-release version is equally effective for those who find the twice-daily schedule difficult. For people who can’t take doxycycline, a single dose of azithromycin is an alternative, though doxycycline is now considered the stronger first-line option.
Treatment cures the active infection, but it cannot reverse scarring or damage that has already occurred. That’s the core reason early detection matters so much. You should also avoid sexual contact during treatment and for seven days after completing it to prevent passing the infection to a partner. Both you and your sexual partner need to be treated, even if your partner has no symptoms, to prevent reinfection.
Reinfection and Why It Matters
Curing chlamydia does not give you any immunity. You can get it again immediately after finishing treatment if you’re exposed. Reinfection is common, and each round of infection adds to the risk of reproductive damage. The bacteria trigger a fresh inflammatory response every time, and that inflammation is what produces scar tissue. For women especially, multiple infections compound the chance of tubal damage, PID, and infertility in a way that a single treated infection may not.
This is why retesting three months after treatment is recommended. Many reinfections happen because an untreated partner passes the bacteria right back, so making sure both partners complete treatment is just as important as your own course of antibiotics.