An STI can leave scar tissue in the epididymis, the coiled tube behind each testicle where sperm mature and wait to be released. If that tube scars shut on both sides, sperm never reach the ejaculate. The ejaculation still looks normal because most of the fluid comes from the prostate and seminal vesicles, not from sperm. That is why some men only discover the damage when a semen analysis comes back with no sperm.
Chlamydia and gonorrhea are the two infections that show up most often in male fertility discussions. They are bacterial, often silent in men, and capable of moving beyond the urethra into the epididymis. Other STIs, including mycoplasma, trichomoniasis, HPV, and HIV, have weaker or less direct evidence, but they still matter in specific situations.
The infections that affect sperm and the tubes that carry them
Chlamydia and gonorrhea
The CDC lists chlamydia and gonorrhea as the most common causes of acute epididymitis in sexually active men under 35. When the infection reaches the epididymis, inflammation swells the narrow tube. As the infection clears, the body can lay down scar tissue. In mild cases, that scarring may not affect anything. In more severe or repeated infections, the tube can narrow or close. If both epididymides are blocked, sperm transport stops. That is known as obstructive azoospermia, and it is one of the few forms of male infertility that can look completely normal on the outside.
Chlamydia is especially sneaky because many infected men never notice symptoms. Gonorrhea is more likely to cause obvious discharge and pain, but it can also pass without signs. Both are treatable, but treatment works best before the infection climbs beyond the urethra.
Mycoplasma genitalium and Ureaplasma
These are less famous but can also cause urethritis. Fertility clinics sometimes test for them when semen parameters are abnormal, especially after chlamydia and gonorrhea have been ruled out. The research linking them to reduced sperm motility or count is inconsistent. Some studies find associations, others do not. They can cause inflammation in the reproductive tract, and that inflammation is a plausible mechanism, but the evidence is not as settled as it is for chlamydia and gonorrhea.
Trichomoniasis
Trichomonas vaginalis is a protozoan, not a bacterium. It can cause urethritis and prostatitis in men. A few studies have noted lower sperm motility in infected men, but the overall evidence is weaker than for the bacterial infections that cause epididymitis. It responds well to metronidazole or tinidazole.
HPV
High-risk HPV types have been detected in semen, and some research has linked HPV in semen to reduced sperm motility and increased DNA fragmentation. The mechanism is not fully understood, and most HPV infections clear on their own. The fertility link is still an area of active research, not a settled cause.
Herpes (HSV)
Herpes is not a classic direct cause of male infertility. The virus can be found in semen during outbreaks, but the bigger practical issue is that recurrent outbreaks can reduce how often a couple has sex. Some studies have reported lower sperm counts in men with HSV in semen, but the data are limited and do not prove a direct cause.
HIV and syphilis
Untreated HIV can reduce semen quality through chronic inflammation, hormonal changes, and opportunistic infections. Antiretroviral therapy changes that picture. Men with well-controlled HIV can have normal semen parameters. Syphilis is a systemic infection that can involve the testicles in later stages, but it is far less commonly the cause of a fertility workup than chlamydia or gonorrhea.
How the damage shows up
Acute epididymitis causes pain and swelling behind one or both testicles, sometimes with fever and a heavy feeling in the scrotum. That is a reason to be seen the same day. Urethritis shows up as discharge, burning with urination, or discomfort at the tip of the penis. Prostatitis can cause pain between the scrotum and the anus, painful ejaculation, and urinary symptoms. But a lot of STI-related fertility damage has no symptoms at the time. The infection clears, the scar remains, and the first sign is a semen analysis showing no sperm or very low sperm.
Treatments: clearing the infection first
Treatment depends on the organism.
Bacterial and protozoal infections
Chlamydia is typically treated with doxycycline or azithromycin. Gonorrhea, because of widespread antibiotic resistance, usually requires an injection of ceftriaxone. Mycoplasma genitalium can be trickier and may require a fluoroquinolone such as moxifloxacin if first-line antibiotics fail. Trichomoniasis responds to metronidazole or tinidazole. Syphilis is treated with penicillin, with the exact regimen depending on the stage. In all of these, sex partners need treatment at the same time. Otherwise reinfection is common.
Viral infections
HPV has no direct antiviral treatment, though warts caused by low-risk HPV can be removed. High-risk HPV usually clears on its own. Herpes is managed with antiviral medications such as valacyclovir or acyclovir, which reduce outbreak frequency and viral shedding. They do not cure the infection. HIV is managed with antiretroviral therapy, which suppresses the virus and, in many cases, restores semen parameters and allows safer conception when viral load is undetectable.
Treatments for fertility damage after infection
If the infection has already left scar tissue, antibiotics clear the active infection but do not dissolve the scar. The options then depend on where the blockage is.
For a blockage in the epididymis, a surgeon can sometimes reconnect the tube to the vas deferens with a procedure called epididymovasostomy. This is specialized microsurgery and works best when the blockage is in one small area. If scar tissue is extensive or the surgery is not successful, sperm can often be retrieved directly from the testicle or epididymis with a needle or small biopsy. Those sperm are then used with in vitro fertilization and intracytoplasmic sperm injection, which injects a single sperm directly into an egg. Men with post-infectious obstructive azoospermia often have normal sperm production in the testicle, so sperm retrieval can be successful even when nothing appears in the ejaculate.
For men with antisperm antibodies or reduced sperm quality after an infection, there is no single medication that reverses the effect. The standard path is to treat any active infection, repeat a semen analysis after a few months, and evaluate fertility as a couple if conception has not happened within a reasonable window. A urologist or reproductive specialist can also check for structural issues with a scrotal ultrasound.
What you can do now
If you have symptoms now, get tested and treated early. The earlier the infection is stopped, the lower the chance it reaches the epididymis. If you have no symptoms but a new partner or multiple partners, routine STI screening catches silent infections. After treatment for chlamydia or gonorrhea, CDC guidelines recommend retesting in about three months because reinfection is common.
Use condoms consistently. They reduce the risk of the infections most likely to affect fertility. If you have had an STI in the past and you and a partner have been trying to conceive without success for 12 months, or 6 months if your partner is over 35, a semen analysis and an infectious disease screen are a reasonable first step. The goal is to identify a fixable problem before more time passes.
Fertility conversations carry a weight that is rarely discussed. Men often feel they caused the problem or that something is broken. The medical reality is that many post-STI fertility problems are either preventable with early treatment or manageable with sperm retrieval. If you are carrying guilt or anxiety about this, talking to a doctor or a counselor is part of the same health picture.
This content is for educational purposes only and is not medical advice. Oakman products are designed for physical comfort and cooling. They make no claims about fertility, sperm quality, or hormone levels. Consult a healthcare professional for personalized advice.