How Male Fertility Works and Why It Matters

Written by: Mate Health Clinical Education Team
Updated: July 2026

Male fertility depends on sperm production, hormone signaling, sperm maturation and transport, and the quality of the final semen sample. A semen analysis measures key parameters such as concentration, motility, morphology, volume, and total count, but no single value determines fertility by itself.

Why Understanding the Basics Matters

Many men reach adulthood with only a general understanding of fertility. That can make it harder to understand why lifestyle changes take months to appear in semen results, why one test is not always the final word, or why certain symptoms and treatments should be discussed with a physician.

Male factors contribute to approximately half of infertility cases, either alone or alongside female factors. AUA/ASRM guidance recommends evaluating both partners during the fertility workup. [1,2]

A 2017 meta-analysis reported that sperm concentration among men in North America, Europe, Australia, and New Zealand had declined by more than 50% between 1973 and 2011. [3] A later analysis reported similar trends across a broader group of countries and found that the decline appeared to accelerate after 2000. [4]

These population studies have limitations and do not predict what is happening with any individual man. Understanding the basic biology still helps explain what can be measured and when evaluation may be appropriate.

The Male Reproductive System

Sperm production, maturation, and delivery involve several structures:

• Testicles: Produce sperm and testosterone.
• Epididymis: Stores sperm as they mature and gain the ability to move.
• Vas deferens: Carries mature sperm toward the urethra during ejaculation.
• Seminal vesicles and prostate: Produce most of the fluid in semen.
• Urethra: The final pathway through which semen leaves the body.

The hypothalamus and pituitary gland regulate the hormones required for testosterone and sperm production.

Spermatogenesis: How Sperm Is Made

Sperm production, called spermatogenesis, is a continuous process inside the seminiferous tubules of the testicles.

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. [5]

That timeline is why a semen analysis may reflect events from roughly three months before the test. A significant fever, certain medications, cancer treatment, hormone use, or another disruption may affect a later result even after the immediate event has passed.

Sperm are produced continuously, with millions generated each day.

The Hormones Controlling Sperm Production

Spermatogenesis is regulated by the hypothalamic-pituitary-gonadal, or HPG, axis.

The hypothalamus releases gonadotropin-releasing hormone, or GnRH, which signals the pituitary gland to release:

• Luteinizing hormone, or LH: Stimulates the testicles to produce testosterone.
• Follicle-stimulating hormone, or FSH: Works with testosterone to support sperm development.

Pituitary or testicular conditions, obesity, significant illness, inadequate energy intake, and certain medications may disrupt this system.

Testosterone replacement therapy and anabolic steroids deserve special attention. External testosterone can suppress LH and FSH, reducing or completely stopping sperm production. Men interested in current or future fertility should not begin or discontinue testosterone treatment without discussing it with a qualified physician. [1,2]

What a Semen Sample Contains

Semen is mostly fluid produced by the seminal vesicles and prostate. Sperm cells account for only a small portion of the total volume.

The WHO Laboratory Manual for the Examination and Processing of Human Semen, 6th Edition (2021), provides population-based reference values for several core measurements. [6]

Parameter	WHO 6th Edition Reference Value
Semen volume	1.4 mL
Sperm concentration	16 M/mL
Total sperm count	39 M per ejaculate
Progressive motility	30%
Total motility	42%
Normal morphology	4%

These are not pass-or-fail fertility cutoffs. A result below a reference value does not prove infertility, and a result above every value does not guarantee pregnancy.

Not every measurement on a detailed semen analysis has its own WHO lower reference value. Calculated measurements, sperm velocity, DNA fragmentation, and other advanced parameters provide additional context.

What Can Interrupt Sperm Production

Several medical, environmental, and lifestyle factors may affect sperm production:

• Varicocele: Enlarged scrotal veins associated with impaired fertility in some men.
• Heat exposure: Frequent or prolonged testicular heat may temporarily affect sperm production or semen parameters. A 2025 laboratory study identified temperature-sensitive CatSper activity in mouse sperm, offering a possible mechanism for further study. It did not establish a precise harmful temperature for men. [7]
• Hormonal conditions: Pituitary disorders, hypogonadism, thyroid conditions, and other endocrine problems.
• Genetic factors: Y-chromosome microdeletions, Klinefelter syndrome, and other conditions that may reduce or prevent sperm production.
• Infections: Certain sexually transmitted infections, epididymitis, orchitis, and mumps affecting the testicles after puberty.
• Lifestyle factors: Smoking, heavy alcohol use, obesity, inadequate sleep, and other health behaviors.
• Medications and treatments: Testosterone, anabolic steroids, chemotherapy, radiation, and certain other treatments.
• Emerging research: A small 2024 observational study detected microplastics in semen from 40 men and reported associations between certain polymers and progressive motility. It did not establish causation or support specific fertility interventions. [8]

Having one risk factor does not mean a man is infertile, and a healthy lifestyle does not rule out a medical cause.

Does Male Fertility Decline With Age?

Unlike women, men do not begin life with a fixed supply of reproductive cells. Sperm-producing stem cells continue dividing throughout adulthood.

Male fertility may still change gradually with age, although there is no single age at which it suddenly declines. A systematic review and meta-analysis associated increasing male age with gradual changes in semen volume, total sperm count, motility, progressive motility, and morphology. [9]

AUA/ASRM guidance also advises couples that advanced paternal age, defined in the guideline as age 40 or older, is associated with increased risks of certain adverse health outcomes in offspring. These include increased sperm DNA fragmentation and de novo genetic mutations. The absolute risk to an individual pregnancy remains low. [1]

Age is only one factor. A man's health, medications, hormones, reproductive history, partner's age, and semen-analysis results provide more useful individual context than age alone.

Why Semen Quality May Matter Beyond Conception

Semen quality has increasingly been studied as a possible marker of broader male health.

Large observational studies have associated poorer semen parameters with metabolic conditions, later illness, and higher mortality. [10,11] These findings do not mean low sperm count causes poor health. They may reflect shared factors such as hormonal disruption, chronic disease, inflammation, genetics, or environmental exposures.

A semen analysis is not a replacement for routine health screening. However, abnormal semen parameters may deserve broader medical review, particularly when accompanied by:

• Reduced libido or erectile difficulties
• Testicular pain, swelling, or changes in size
• Breast tissue enlargement
• Reduced facial or body hair
• Persistent fatigue or loss of muscle mass
• A history of delayed puberty
• Testosterone or anabolic steroid use

Male reproductive health and general health often overlap.

How Testing Fits Into Fertility Evaluation

Symptoms alone are a poor guide to sperm production. Many men with abnormal semen parameters feel healthy and have no obvious reproductive symptoms.

A semen analysis is the primary laboratory test used to evaluate sperm production and semen quality. Abnormal findings or relevant symptoms may lead to repeat testing, a physical examination, hormone testing, genetic testing, imaging, or additional sperm-function testing.

Mate Health's Comprehensive Semen Analysis reports 20 semen parameters, including volume, concentration, total sperm count, four motility classifications, morphology, velocity, and calculated functional sperm measurements.

The Advanced Semen Analysis adds DNA fragmentation, vitality, and sperm microscopy images.

Specimens are processed in a CLIA-certified, CAP-accredited high-complexity andrology laboratory using WHO 6th Edition (2021) methodology.

Patients receive a laboratory report along with access to MateIQ, which helps explain report values and questions they may want to discuss with their physician. MateIQ does not diagnose infertility or replace medical review.

Because semen parameters vary naturally between ejaculates, repeat testing may be appropriate when the first result is abnormal. [1]

FAQs

How Long Does It Take the Body to Make Sperm?

A single cycle from stem cell to a fully formed sperm cell takes approximately 74 days. Sperm then spend another 2 to 3 weeks maturing in the epididymis. The total process takes roughly three months.

What Organs Are Involved in Male Fertility?

The main structures include the testicles, epididymis, vas deferens, seminal vesicles, prostate, and urethra. The hypothalamus and pituitary gland regulate the hormones required for sperm production.

Does Male Fertility Decline With Age?

Male fertility may gradually change with age, but there is no universal age at which it suddenly declines. Increasing age has been associated with changes in several semen parameters and sperm DNA integrity. [1,9]

Can Testosterone Improve Male Fertility?

Testosterone can improve symptoms of low testosterone, but external testosterone may suppress or stop sperm production. Men interested in fertility should discuss treatment options with a physician.

Can Low Sperm Count Indicate Another Health Issue?

Sometimes. Poorer semen quality has been associated with metabolic disease, hormonal conditions, and later illness. An abnormal result does not diagnose these conditions, but it may justify a broader health review.

Does a Normal Semen Analysis Guarantee Fertility?

No. Results within reference values can be reassuring, but they do not guarantee pregnancy or rule out every male fertility issue.

Medical Disclaimer

This article is for educational purposes and does not constitute medical advice or diagnosis.

Consult a physician or reproductive urologist if you have fertility concerns, hormonal symptoms, testicular pain or changes, or questions about medications that could affect sperm production.

Couples who have not conceived after 12 months of regular unprotected intercourse, or after six months when the female partner is 35 or older, should seek a fertility evaluation. Earlier evaluation may be appropriate when either partner has a known risk factor.

Want a clearer picture of where you stand? Explore Mate Health's at-home semen analysis options or learn more about our laboratory standards and specimen transport validation on the Mate Health science page.

References

1. American Urological Association; American Society for Reproductive Medicine. Diagnosis and Treatment of Infertility in Men: AUA/ASRM Guideline, Part I. 2020; amended 2024.
2. Brannigan RE, Hermanson L, Kaczmarek J, Kim SK, Kirkby E, Tanrikut C. Updates to Male Infertility: AUA/ASRM Guideline (2024). J Urol. 2024;212(6):789-799. doi:10.1097/JU.0000000000004180. PMID: 39145501.
3. Levine H, Jørgensen N, Martino-Andrade A, et al. Temporal trends in sperm count: a systematic review and meta-regression analysis. Hum Reprod Update. 2017;23(6):646-659. doi:10.1093/humupd/dmx022. PMID: 28981654.
4. Levine H, Jørgensen N, Martino-Andrade A, et al. Temporal trends in sperm count: a systematic review and meta-regression analysis of samples collected globally in the 20th and 21st centuries. Hum Reprod Update. 2023;29(2):157-176. doi:10.1093/humupd/dmac035. PMID: 36377604.
5. Amann RP. The cycle of the seminiferous epithelium in humans: a need to revisit? J Androl. 2008;29(5):469-487. doi:10.2164/jandrol.107.004655. PMID: 18497337.
6. World Health Organization. WHO Laboratory Manual for the Examination and Processing of Human Semen. 6th ed. Geneva: World Health Organization; 2021.
7. Swain DK, Vergara C, Castro-Arnau J, Lishko PV. The essential calcium channel of sperm CatSper is temperature-gated. Nat Commun. 2025;16:3657. doi:10.1038/s41467-025-58824-0. PMID: 40246904.
8. Li N, Yang H, Dong Y, et al. Prevalence and implications of microplastic contaminants in general human seminal fluid: A Raman spectroscopic study. Sci Total Environ. 2024;937:173522. doi:10.1016/j.scitotenv.2024.173522. PMID: 38802004.
9. Johnson SL, Dunleavy J, Gemmell NJ, Nakagawa S. Consistent age-dependent declines in human semen quality: a systematic review and meta-analysis. Ageing Res Rev. 2015;19:22-33. doi:10.1016/j.arr.2014.10.007. PMID: 25462195.
10. Eisenberg ML, Li S, Behr B, Pera RR, Cullen MR. Relationship between semen production and medical comorbidity. Fertil Steril. 2015;103(1):66-71. doi:10.1016/j.fertnstert.2014.10.017. PMID: 25497466.
11. Jensen TK, Jacobsen R, Christensen K, Nielsen NC, Bostofte E. Good semen quality and life expectancy: a cohort study of 43,277 men. Am J Epidemiol. 2009;170(5):559-565. doi:10.1093/aje/kwp168. PMID: 19605539.