Mumps was a routine childhood experience in the United States until the MMR vaccine arrived in 1967, with hundreds of thousands of cases reported every year before vaccination became standard. If you were born before that shift, or if you grew up in a family that opted out, your testicles may carry the history of that infection decades later. The same question applies to high fevers, undescended testicles at birth, and testicular torsion in adolescence. Whether any of those events matters for your fertility now depends on what happened, when, and how quickly it was treated.
The temperature requirement your testicles never told you about
Sperm production runs best a few degrees below core body temperature. That is why the testicles sit in the scrotum, outside the body, where they stay roughly 2 to 4 degrees Celsius cooler than the torso (Durairajanayagam et al., Reproductive BioMedicine Online, 2015). The cells that produce sperm are sensitive to heat. When scrotal temperature rises for a sustained period, sperm production slows or stops. The effect is usually reversible, but the depth of the insult and the timing matter.
Childhood infections become relevant because several of them either heat the testicles directly or injure them through inflammation. The clearest example is mumps.
Mumps: the childhood infection with the clearest link
Mumps is a viral infection that swells the salivary glands. In roughly 20 to 30 percent of males who contract mumps after puberty, the virus also invades the testicles, causing a condition called mumps orchitis. The incidence is highest in post-pubertal males, which is why the age at infection matters. A boy who gets mumps at age 5 has a different risk profile than a teenager who gets it at age 15.
What mumps orchitis does to the testicle
Mumps orchitis typically causes severe testicular pain, swelling, and fever. In about 30 to 50 percent of orchitis cases, the affected testicle shrinks afterward, a process called testicular atrophy. When atrophy occurs, the seminiferous tubules where sperm are produced are damaged. The result can be reduced sperm count, reduced sperm quality, or in bilateral cases where both testicles are affected, azoospermia, the complete absence of sperm in the ejaculate. Bilateral orchitis is less common than unilateral, but it carries the heaviest fertility consequences.
The vaccine changed the landscape. According to the CDC, mumps cases dropped by more than 99 percent in the United States after the MMR vaccine became standard. Mumps orchitis is now rare in vaccinated populations. If you were vaccinated as a child, your risk from mumps is low. If you were not vaccinated and you contracted mumps after puberty, a semen analysis can tell you where things stand now.
Undescended testicles: a mechanical problem with lasting effects
Cryptorchidism is the medical term for an undescended testicle. About 2 to 8 percent of full-term male infants are born with at least one testicle that has not descended into the scrotum. In premature infants, the rate is higher, up to 30 percent. Most undescended testicles descend on their own within the first few months of life. For those that do not, surgery called orchidopexy is typically performed before age 2.
Why correction timing matters
The fertility link here is well documented. Men with a history of bilateral undescended testicles, even after surgical correction, have higher rates of infertility than men with no such history. The explanation is partly about temperature. An undescended testicle sits inside the abdomen or inguinal canal, where it is warmer than the scrotum. The elevated temperature impairs development of sperm-producing cells, particularly if the testicle stays undescended for years. Even after surgery brings the testicle down, some of that developmental damage may be permanent. The earlier the correction, the better the long-term sperm production.
For unilateral cryptorchidism, the effect on fertility is less severe because the descended testicle usually compensates. But the undescended testicle itself may still produce fewer sperm. A semen analysis can tell you where you stand.
Any childhood fever can leave a temporary mark
Fever is uncomfortable but usually brief. For spermatogenesis, a single high fever can leave a measurable, temporary drop in sperm count. The full cycle of sperm production takes about 74 days. When body temperature spikes, the heat-sensitive cells that produce sperm slow down. The result is a reduced sperm count that shows up on a semen analysis two to three months later, then recovers over the following months.
This is not a permanent injury for most men. A single febrile illness in childhood, even a high fever, does not usually cause lasting infertility. The effect is temporary because new sperm-producing cells replace the old ones. A severe or prolonged febrile illness, particularly one that involves the testicles directly like mumps orchitis, is a different story. The same principle applies to saunas. Regular sauna use at high frequency has been shown to temporarily lower sperm count and can worsen morphology, with the effect reversing once heat exposure stops (Garolla et al., Human Reproduction, 2013).
Whether repeated high fevers in childhood cause lasting damage when the testicles themselves are not involved remains unsettled, since most research has focused on direct testicular infections like mumps.
Adolescent STIs and testicular torsion
Two other childhood and adolescent events deserve mention. Neither is a classic childhood illness, but both occur in young men and can affect fertility.
- Chlamydia and gonorrhea are the most common bacterial STIs in young men. When untreated, these infections can spread to the epididymis, the coiled tube behind each testicle that stores and transports sperm. The resulting inflammation, called epididymitis, can scar the epididymis and block the passage of sperm. A blocked epididymis means sperm cannot get out, even when the testicle is producing them normally. Antibiotics clear the infection, but the scarring is not always reversible. The risk is higher when the infection goes untreated for a long time.
- Testicular torsion is a surgical emergency. The testicle twists on its spermatic cord, cutting off blood flow. If the testicle is not untwisted within about six hours, the tissue can die. Torsion is most common in adolescent boys, with a peak incidence between ages 12 and 18. Approximately 1 in 4,000 males under 25 experiences torsion. Prompt surgery saves the testicle in most cases. Delayed treatment can lead to loss of the testicle. A history of torsion, even with successful surgical correction, warrants a semen analysis when fertility becomes a concern.
What you can do now
If you are reading this because you had one of these childhood events, the first step is to know what actually happened. A detailed pediatric history helps, but not everyone remembers or was told the details. The second step is a semen analysis.
- Know what actually happened. Talk to your parents if possible, or dig up pediatric records. The specific event matters: mumps orchitis, bilateral cryptorchidism, torsion, or an untreated STI each have different implications.
- Get a semen analysis. A semen analysis measures sperm count, motility, and morphology. It is a straightforward test that gives you a clear baseline. If the numbers are in the normal range, childhood events are unlikely to be causing problems. If the numbers are low, the history can help your doctor understand why. Sperm parameters fluctuate, so one abnormal analysis is usually followed by a second one a few weeks later. Two consistent results give a clearer picture.
- Mention relevant history to a specialist. If you had mumps orchitis, bilateral cryptorchidism, or testicular torsion, bring that up with a urologist or reproductive endocrinologist when you are ready to start a family. There may be options available depending on what the semen analysis shows, including assisted reproductive technologies.
Childhood infections do not explain most cases of male infertility. The more common contributors in adult men are heat exposure, tight underwear, obesity, smoking, and environmental exposures. A childhood history is one piece of the puzzle, not the whole picture. But when the history includes a direct testicular infection, bilateral undescended testicles, or torsion, it is a piece worth investigating.
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.