How Male Fertility Works and Why It Matters

Written by: Mate Health Clinical Education Team

Updated: July 2026

Why Understanding the Basics Changes How Men Approach Fertility

Most men reach adulthood with a vague sense that fertility is "a female thing" until it isn't. Part of the reason male-factor infertility gets diagnosed late is structural (fertility workups have historically started with the woman), but part of it is that most men have never been taught the basic mechanics of how sperm gets made in the first place. That gap makes it hard to understand why lifestyle changes take months to show results, why a single test isn't the final word, or why certain symptoms are worth mentioning to a doctor.

This isn't abstract biology for its own sake. Male factors are involved in roughly 40-50% of all infertility cases, according to guidance from the American Urological Association and American Society for Reproductive Medicine, and a global meta-analysis published in Human Reproduction Update found sperm concentration among Western men had declined by more than 50% between 1973 and 2011, a trend a 2022 follow-up study found had extended globally and accelerated after 2000. Understanding the system that's under strain is the first step to protecting it.

The Male Reproductive System, Briefly

Sperm production and delivery involves several distinct structures, each with a specific job:

• Testicles: house the seminiferous tubules where sperm are actually produced, and the Leydig cells that produce testosterone. Located outside the body specifically to stay a few degrees cooler than core temperature, which spermatogenesis requires.
• Epididymis: a tightly coiled tube sitting against each testicle where newly produced sperm mature and gain the ability to swim, over roughly two to three weeks.
• Vas deferens: the muscular tube that transports mature sperm from the epididymis toward the urethra during ejaculation.
• Seminal vesicles: contribute roughly 60-70% of semen volume, providing fructose (fuel for sperm) and other components.
• Prostate gland: contributes enzymes and fluid that make up much of the remaining semen volume, including compounds that help liquefy semen after ejaculation.
• Urethra: the shared final pathway for both semen and urine, though a valve mechanism prevents them from mixing during ejaculation.

Spermatogenesis: How Sperm Is Actually Made

Sperm production, called spermatogenesis, is a continuous assembly-line process happening inside the seminiferous tubules, the coiled structures that make up most of testicular volume. A single cycle from stem cell to a fully formed, though not yet mobile, sperm cell takes approximately 74 days. After that, the sperm spends another 2 to 3 weeks maturing in the epididymis, gaining the ability to swim and fertilize an egg.

That timeline is the reason semen analysis results reflect events from roughly three months before the test, not last week. A fever, a course of certain medications, or a period of heavy alcohol use two months ago can still show up as reduced sperm quality today, even if you feel completely recovered.

The scale of the process is worth appreciating too: healthy testicles produce roughly 1,500 sperm per second on average, translating to tens of millions per day. That volume matters because the vast majority of sperm in any given ejaculate never get anywhere near an egg; the sheer number produced is partly a numbers-game adaptation.

The Hormone System Running the Whole Process

Spermatogenesis is controlled by a feedback loop called the hypothalamic-pituitary-gonadal (HPG) axis. The hypothalamus releases gonadotropin-releasing hormone (GnRH), which signals the pituitary gland to release two hormones: luteinizing hormone (LH), which tells the testicles' Leydig cells to produce testosterone, and follicle-stimulating hormone (FSH), which directly stimulates the seminiferous tubules to support sperm development.

This system is sensitive to disruption from multiple directions. Chronic stress elevates cortisol, which can suppress GnRH release at the very top of the chain. Obesity increases aromatase activity, an enzyme that converts testosterone into estrogen, throwing off the balance the whole feedback loop depends on. Certain medications, including some used for prostate conditions, hair loss, and anabolic steroids specifically, can suppress this axis directly, sometimes causing significant, if often reversible, drops in sperm production.

What a Healthy Semen Sample Contains

Semen itself is mostly fluid contributed by the seminal vesicles and prostate; sperm cells actually make up a small fraction of total ejaculate volume, typically well under 5%. A WHO 6th Edition-referenced semen analysis evaluates several parameters against established lower reference limits:

Parameter	WHO 6th Edition Lower Reference Limit
Semen volume	1.4 mL
Sperm concentration	16 million/mL
Total sperm number	39 million per ejaculate
Progressive motility	30%
Total motility	42%
Normal morphology (strict criteria)	4%
pH	≥7.2

 

These are population-based lower reference limits, not pass/fail cutoffs for an individual's fertility. A result slightly below a reference value doesn't mean infertility; it means the value falls outside where most fertile men's samples fall, which is a meaningfully different statement that a physician can help interpret in context.

What Can Interrupt the Process

Because spermatogenesis is a long, hormone-dependent, temperature-sensitive process with multiple stages, there are a lot of places it can go wrong:

• Varicocele: enlarged scrotal veins that disrupt the counter-current heat exchange system, chronically raising testicular temperature. One of the most common correctable causes of reduced sperm quality.
• Heat exposure: a 2025 Nature Communications study identified the CatSper calcium channel as temperature-gated, activating at 33.5°C, which offers a cellular explanation for why sustained heat exposure impairs sperm function.
• Hormonal disorders: conditions affecting the HPG axis, including pituitary issues, thyroid disorders, and hypogonadism.
• Genetic factors: including Y-chromosome microdeletions and Klinefelter syndrome, which can significantly impair or eliminate sperm production.
• Infections: including sexually transmitted infections and mumps orchitis (particularly if contracted after puberty), which can damage testicular tissue.
• Environmental and lifestyle exposures: smoking, excessive alcohol, obesity, chronic stress, poor sleep, and increasingly, microplastic exposure; a 2024 study in Science of the Total Environment found microplastic contamination in every semen sample tested among 36 healthy men, with PVC particle presence correlated to reduced motility.
• Medications and treatments: chemotherapy, certain testosterone therapies (paradoxically, external testosterone can suppress natural sperm production by shutting down the HPG feedback loop), and some prostate medications.

Does Male Fertility Decline With Age?

Unlike the female biological clock, which is tied to a fixed, depleting egg supply, male fertility declines more gradually and less predictably, but it does decline. Sperm quality, particularly DNA integrity and motility, tends to decrease gradually starting around age 40-45 in population studies, and paternal age has been linked to modestly increased risks of certain conditions in offspring, including some genetic mutations that accumulate in sperm-producing cells over a man's lifetime through repeated cell division. This isn't a reason for alarm at any specific age, but it's a reason age is a relevant data point during a fertility evaluation for men just as much as for women.

Why This Matters Beyond Conception

Semen quality isn't purely a fertility metric, it's increasingly recognized as a general health indicator. Multiple studies have linked lower sperm counts to broader health markers, including higher rates of metabolic syndrome, cardiovascular risk factors, and even modestly increased all-cause mortality risk in some cohort research, independent of fertility intentions. The proposed explanation is that the same systemic factors that damage sperm production, chronic inflammation, oxidative stress, hormonal imbalance, tend to affect other organ systems too. A semen analysis, in other words, can function as an early signal worth discussing with a physician even for men who aren't currently trying to conceive.

How Testing Fits Into Understanding Your Own Fertility

Given how many variables feed into sperm production, symptoms alone are a poor guide to what's actually happening. Most fertility-affecting conditions, from mild hormonal imbalances to early-stage varicoceles, produce no noticeable symptoms at all. A semen analysis is the only way to get an objective read on where you currently stand.

Mate Health's Comprehensive Semen Analysis measures concentration, motility, morphology, volume, and pH against WHO 6th Edition reference values, processed in a CLIA-certified, CAP-accredited andrology laboratory. For a fuller picture, including DNA fragmentation, which standard testing doesn't capture, the Advanced Semen Analysis adds that layer. Results are explained in plain language through the MateIQ tool, and Mate Health recommends sharing any results, expected or not, with a physician who can interpret them against your full health history.

FAQs

How long does it take for the body to make sperm?
About 74 days from stem cell to mature sperm cell, plus another 2-3 weeks maturing in the epididymis before it's capable of fertilizing an egg. Total turnaround is roughly 10-12 weeks.

How many sperm does a man produce per day?
Healthy testicles produce roughly 1,500 sperm per second on average, which adds up to tens of millions per day, though only a tiny fraction of any single ejaculate ever gets close to an egg.

What organs are involved in male fertility?
The testicles (sperm and testosterone production), epididymis (sperm maturation), vas deferens (transport), seminal vesicles and prostate (semen fluid production), and the hypothalamus and pituitary gland, which hormonally regulate the entire system.

Does male fertility decline with age?
Yes, though more gradually and variably than female fertility. Sperm DNA integrity and motility tend to decline starting around age 40-45, and paternal age is a factor fertility specialists consider, though it's rarely disqualifying on its own.

Can low sperm count be a sign of a broader health issue?
Sometimes. Research has linked reduced semen quality to metabolic and cardiovascular risk markers, since many of the same factors that impair sperm production, inflammation, hormonal imbalance, oxidative stress, affect other systems too.

Medical Disclaimer

This article is for educational purposes and does not constitute medical advice or diagnosis. If you have concerns about fertility, hormonal symptoms, or a family or personal history of conditions affecting reproductive health, consult a physician or urologist.

References

1. World Health Organization. WHO Laboratory Manual for the Examination and Processing of Human Semen, 6th Edition. who.int
2. American Urological Association / American Society for Reproductive Medicine. Male Infertility Guideline. auajournals.org
3. Levine H, et al. "Temporal trends in sperm count: a systematic review and meta-regression analysis." Human Reproduction Update, 2017. academic.oup.com
4. Levine H, et al. "Temporal trends in sperm count... samples collected globally in the 20th and 21st centuries." Human Reproduction Update, 2022. academic.oup.com
5. Swain DK, Vergara C, Castro-Arnau J, Lishko PV. "The essential calcium channel of sperm CatSper is temperature-gated." Nature Communications, 2025. nature.com
6. Li N, et al. "Prevalence and implications of microplastic contaminants in general human seminal fluid." Science of the Total Environment, 2024. medicalxpress.com
7. Centers for Medicare & Medicaid Services. Clinical Laboratory Improvement Amendments (CLIA). cms.gov