Short answer: yes, some can. But the relationship is more specific than most men realize. It's not that an STI from your twenties automatically means trouble later. It's that certain infections, when untreated or poorly managed, cause physical damage that accumulates over time. The window for intervention is often wider than you think, but it closes.
Let me walk through what the research actually shows, which infections matter most, and what you can do about it if you're in this situation.
The mechanism: it's almost always about blockage or inflammation
Male infertility from STIs doesn't work like a switch. It works like a slow clog in a drain. The two main pathways are:
- Epididymitis - inflammation of the epididymis, the coiled tube where sperm mature and are stored. When an infection causes swelling here, it can scar the tube, blocking sperm from getting out. This is the most direct link between STIs and later infertility.
- Prostatitis - inflammation of the prostate can alter the chemical composition of semen, making it harder for sperm to move or survive. It can also cause pain that interferes with ejaculation.
- Direct sperm damage - some bacteria and viruses can bind to sperm cells, impairing their motility or triggering an immune response that attacks your own sperm.
The key detail: damage is rarely instant. It builds over months or years, which is why a man might not connect a chlamydia infection at age 22 with fertility problems at 34.
Which STIs carry the highest risk
Chlamydia - This is the biggest offender. Chlamydia trachomatis is the most common bacterial STI worldwide, and it's also the one most strongly linked to male infertility. A 2018 meta-analysis in Human Reproduction Update found that chlamydia infection was associated with significantly lower sperm concentration and motility. The problem is that chlamydia is often asymptomatic in men. Up to 50 percent of infected men have no symptoms. So it can quietly cause epididymitis and scarring without ever being treated.
Gonorrhea - Similar mechanism to chlamydia. Neisseria gonorrhoeae can cause epididymitis and prostatitis. Untreated gonorrhea can also lead to urethral strictures-scar tissue that narrows the urethra-which can cause retrograde ejaculation (semen going backward into the bladder instead of out). That's a mechanical problem that doesn't fix itself.
Trichomoniasis - Less discussed but real. Trichomonas vaginalis is a parasite, not a bacteria. Studies have found it can reduce sperm motility and viability. A 2016 study in Fertility and Sterility reported that trichomonas infection was associated with a 2.5-times higher risk of infertility in men. It's also frequently asymptomatic.
Mycoplasma genitalium - Emerging research. This bacterium is becoming recognized as a cause of urethritis and epididymitis. Some studies suggest it can lower sperm quality, though the evidence isn't as strong as for chlamydia.
HPV - The picture here is more complicated. High-risk HPV types have been found on sperm cells, and some studies show reduced motility in infected men. But the effect seems less dramatic than bacterial infections. The good news: most HPV infections clear on their own within two years.
HIV - Untreated HIV can lower testosterone levels and cause testicular damage. But with modern antiretroviral therapy, fertility outcomes are much better than they were two decades ago.
The infections that probably don't matter for fertility
Herpes simplex virus (HSV) doesn't typically cause the kind of scarring or inflammation that blocks sperm. Syphilis, if treated early, also doesn't appear to cause lasting fertility issues in men. The concern with syphilis is more about transmission to a partner during pregnancy.
What the data actually says about long-term risk
Here's the honest answer: we don't have great long-term prospective studies tracking men from their first STI to their fertility outcomes decades later. Most of the evidence comes from cross-sectional studies (comparing fertile vs. infertile men and looking at past infection rates) and from small mechanistic studies.
What those studies consistently show: men with a history of chlamydia or gonorrhea are overrepresented in infertility clinics. A 2020 review in Andrology estimated that prior chlamydia infection accounts for roughly 10 to 15 percent of male infertility cases where no other cause is found. That's not a majority, but it's not negligible either.
The strongest predictor of future fertility problems is not just having had an STI, but having had an STI that caused symptoms you ignored. Men who had epididymitis symptoms (testicular pain, swelling) and didn't get treated are at higher risk than men who had asymptomatic infections that were caught on routine screening.
What you can actually do about it
This is the part that matters. If you're reading this and wondering about your own history, here's the practical path:
- Get tested now if you never did. If you had sex without barriers years ago and never got tested, do it now. A simple urine test can check for chlamydia and gonorrhea. A blood test checks for syphilis and HIV. If you're carrying an untreated infection right now, treating it can stop further damage.
- If you have symptoms now, see a doctor. Testicular pain, swelling, burning during urination, or discharge are not normal. Don't assume it will pass.
- If you're trying to conceive and have been unsuccessful for 12 months, get a semen analysis. This is the single most informative test for male fertility. It will tell you sperm concentration, motility, and shape. If numbers are low, your doctor can check for signs of past infection (white blood cells in semen, markers of epididymal obstruction).
- Treat past infections seriously but not catastrophically. Most men who have had an STI do not become infertile. The risk is elevated, not guaranteed. And even if damage has occurred, there are interventions. Blockages in the epididymis can sometimes be surgically corrected. Sperm can be retrieved directly from the testicle if needed.
The one thing I want you to take away
The most dangerous thing about STIs and male fertility is not the infection itself. It's the silence. Men don't talk about this. They don't get tested. They don't follow up on symptoms. And by the time they're trying to start a family, the damage is done.
If you had unprotected sex in the past and never got a full STI panel, get one. It takes twenty minutes. It costs less than dinner out. And it might save you years of frustration down the road.
This information is for educational purposes. If you have specific concerns about your fertility or a history of STIs, consult a urologist or reproductive health specialist.