Leydig Cells

Leydig cells are specialized cells in the testicles that produce testosterone, the main male sex hormone. They sit in the tissue between the seminiferous tubules, where sperm are made, and play a central role in male puberty, sexual function, muscle and bone health, and fertility. If Leydig cells do not work properly, testosterone levels may fall, which can affect libido, energy, mood, sperm production, and overall reproductive health.

In plain English: Leydig cells are part of the testicular hormone system. They do not make sperm directly, but they help create the hormonal environment sperm need to develop normally.

Key Takeaways

Leydig cells are testicular cells that produce testosterone in response to luteinizing hormone (LH).
They are essential for male sexual development, libido, energy, muscle mass, bone health, and fertility.
Leydig cells do not make sperm, but low testosterone from Leydig cell dysfunction can disrupt normal sperm production.
Problems can stem from aging, testicular injury, genetic conditions, chemotherapy, radiation, inflammation, varicocele, or hormonal disorders.
Symptoms of impaired Leydig cell function may include low libido, erectile issues, fatigue, reduced body hair, mood changes, infertility, or small testes.
Evaluation often includes blood tests such as total testosterone, LH, FSH, and sometimes prolactin, estradiol, or pituitary testing.
Treatment depends on the cause and fertility goals; testosterone therapy is not always appropriate for men trying to conceive.
For men concerned about fertility, both hormone testing and semen analysis usually matter.

What Are Leydig Cells?

Leydig cells, also called interstitial cells of Leydig, are endocrine cells found in the testicles. Their main job is to convert cholesterol into testosterone and other androgens. These hormones are critical for male reproductive function and broader aspects of health.

They are named after Franz Leydig, the anatomist who described them. In adult men, Leydig cells are most active after puberty, when testosterone production becomes central to sexual maturation and reproductive function.

Although Leydig cells are usually discussed in the context of men, related steroid-producing cells also exist in other settings. In male reproductive health, though, the term almost always refers to the testosterone-producing cells in the testes.

Where Are Leydig Cells Found?

Leydig cells are located in the interstitial tissue of the testes, meaning the spaces between the seminiferous tubules. The seminiferous tubules are where sperm are produced. This layout matters because sperm production and hormone production are closely linked but handled by different cell types.

Inside the testicle:

Leydig cells make testosterone.
Sertoli cells support developing sperm within the seminiferous tubules.
Germ cells are the cells that eventually develop into sperm.

This division of labor helps explain why hormone problems can affect semen quality even if sperm cells themselves are not the original problem.

What Do Leydig Cells Do?

The primary function of Leydig cells is testosterone synthesis. They respond to signals from the brain, especially luteinizing hormone, and turn cholesterol into testosterone through a series of enzymatic steps known as steroidogenesis.

Main functions of Leydig cells

Produce testosterone
Support male puberty and development of secondary sexual characteristics
Help maintain libido and erectile function
Support normal sperm production indirectly
Contribute to muscle mass, bone density, red blood cell production, and mood regulation

How testosterone made by Leydig cells is used

Testosterone can act directly in tissues or be converted into:

Dihydrotestosterone (DHT), a more potent androgen important for genital development, body hair, and prostate-related effects
Estradiol, a form of estrogen that still plays an important role in men, especially for bone health and hormonal balance

Within the testes, high local testosterone levels are especially important for spermatogenesis, the process of making sperm. That is one reason Leydig cell health matters so much in male fertility workups.

Why Leydig Cells Matter for Men’s Health and Fertility

Leydig cells sit at the center of male reproductive endocrinology. If they are functioning well, testosterone production is usually adequate. If they are impaired, a man may develop low testosterone, reduced fertility, or both.

Area of health	Why Leydig cells matter
Puberty	Help drive voice deepening, genital growth, muscle development, and body hair through testosterone production
Sexual health	Influence libido, erectile function, and sexual well-being
Fertility	Create the hormonal environment needed for normal sperm production
Body composition	Support muscle mass and help regulate fat distribution
Bone health	Contribute to bone density and long-term skeletal health
Energy and mood	Testosterone levels can affect energy, motivation, and emotional well-being

In fertility settings, Leydig cells matter because testosterone inside the testes must remain high for sperm development to proceed efficiently. A man can sometimes have testosterone in the low-normal range in bloodwork but still have impaired intratesticular hormone support, especially in certain endocrine disorders or after exogenous testosterone use.

How Leydig Cells Are Controlled

Leydig cells are regulated by the hypothalamic-pituitary-gonadal (HPG) axis, the hormonal communication system between the brain and the testes.

The hypothalamus releases gonadotropin-releasing hormone (GnRH).
The pituitary gland responds by releasing luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
LH stimulates Leydig cells to produce testosterone.
FSH mainly acts on Sertoli cells to support sperm production.
Testosterone feeds back to the brain and pituitary to help regulate future hormone output.

This means low testosterone can result from more than one level of dysfunction:

Primary hypogonadism: the testes themselves are not responding properly.
Secondary hypogonadism: the pituitary or hypothalamus is not sending strong enough signals.
Combined or functional causes: obesity, medications, illness, and stress can affect the axis in more complex ways.

Leydig cells vs Sertoli cells

Feature	Leydig cells	Sertoli cells
Location	Between seminiferous tubules	Inside seminiferous tubules
Main role	Produce testosterone	Nourish and support developing sperm
Main hormone signal	LH	FSH
Direct role in sperm production	Indirect	Direct support role
Key secretions	Testosterone and other androgens	Inhibin B, androgen-binding protein, supportive factors

What’s Normal vs What’s Not?

There is no single blood test that directly counts “healthy Leydig cells” in everyday clinical practice. Instead, doctors infer Leydig cell function by looking at hormone levels, symptoms, physical findings, and sometimes fertility testing.

Typical clues that Leydig cell function may be normal

Total testosterone within a healthy reference range for the lab and age context
Normal LH levels
Normal pubertal development
Normal libido and sexual function
Adequate muscle mass, body hair pattern, and testicular development
Normal or near-normal sperm production when fertility is being evaluated

Clues that Leydig cell dysfunction may be present

Low testosterone, especially on repeated morning tests
Elevated LH, suggesting the pituitary is pushing the testes harder than usual
Symptoms of hypogonadism
History of testicular injury, chemotherapy, mumps orchitis, or undescended testicles
Infertility with endocrine abnormalities

Interpretation depends on context. A single testosterone result can be misleading if it was drawn at the wrong time of day, during illness, after poor sleep, or while taking medications that affect hormone levels.

Signs Leydig Cell Function May Be Impaired

Low Leydig cell activity often shows up as low testosterone symptoms. The exact pattern depends on age, severity, and whether the problem started before puberty, during adolescence, or in adulthood.

Possible symptoms in adult men

Low sex drive
Erectile dysfunction or weaker spontaneous erections
Fatigue or low energy
Reduced exercise performance or loss of muscle mass
Increased body fat, especially central fat gain
Depressed mood or irritability
Difficulty concentrating
Reduced body or facial hair over time
Infertility or abnormal semen parameters
Hot flashes in more severe testosterone deficiency

Possible signs before or during puberty

Delayed puberty
Underdeveloped genitalia
Less facial and body hair than expected
Reduced growth of muscle mass and deepening of the voice

These symptoms are not specific to Leydig cell disease alone. Similar issues can come from pituitary disorders, medication effects, sleep apnea, obesity, thyroid disease, depression, or chronic illness. That is why proper testing matters.

What Can Affect Leydig Cell Function?

Leydig cells can be affected by direct testicular damage, broader hormone signaling issues, medical treatments, environmental exposures, and age-related decline. Some causes are temporary, while others are more permanent.

Common causes and contributors

Aging: testosterone production may decline with age, and Leydig cells can become less responsive to LH.
Primary testicular failure: the testes cannot produce adequate testosterone despite normal or high LH.
Undescended testicles (cryptorchidism): can impair long-term testicular function if not corrected early.
Mumps orchitis: inflammation of the testes after mumps can damage testicular tissue.
Testicular trauma or torsion: interrupted blood flow or injury can affect hormone production.
Chemotherapy or radiation: may damage Leydig cells and germ cells.
Varicocele: may contribute to broader testicular dysfunction in some men.
Genetic conditions: such as Klinefelter syndrome and certain disorders of sex development.
Anabolic steroid or testosterone use: external androgens suppress LH and can shut down the natural Leydig cell stimulation pathway.
Pituitary or hypothalamic disorders: reduce LH signaling to Leydig cells.
Obesity and metabolic disease: may lower testosterone via complex hormonal mechanisms.
Alcohol and some drugs: excessive use may affect the testes and hormone axis.
Inflammation and systemic illness: can temporarily or chronically alter hormone production.

Primary vs secondary causes

Type of problem	What it means	Typical lab pattern
Primary hypogonadism	The testes, including Leydig cells, are not functioning normally	Low testosterone with high LH
Secondary hypogonadism	The brain is not sending enough hormonal stimulation	Low testosterone with low or inappropriately normal LH
Mixed/functional hypogonadism	Multiple factors are involved, such as obesity, illness, stress, medications, or aging	Variable pattern

Testing and Diagnosis

Doctors do not usually diagnose “Leydig cell dysfunction” based on one isolated finding. Instead, they evaluate the full picture: symptoms, exam, hormone results, semen analysis if fertility is a concern, and sometimes imaging or genetic testing.

Tests that may be used

Total testosterone: usually checked in the morning on at least two occasions if low testosterone is suspected
Free testosterone: may help in selected cases, especially when sex hormone-binding globulin (SHBG) is abnormal
LH: helps determine whether the problem is testicular or central
FSH: more closely reflects Sertoli cell and spermatogenic function, but is relevant in fertility workups
Prolactin: elevated levels can suppress gonadal function
Estradiol: may be relevant in obesity, gynecomastia, or endocrine imbalance
SHBG: affects interpretation of total testosterone
Semen analysis: essential if fertility is a concern
Testicular ultrasound: may be used if there is concern for masses, varicocele, atrophy, or structural changes
Pituitary MRI: considered if central causes are suspected
Genetic testing: sometimes needed in severe infertility or primary testicular failure

What abnormal results can mean

Low testosterone + high LH often suggests the testes are not responding well, which can reflect Leydig cell impairment.

Low testosterone + low or normal LH suggests a pituitary or hypothalamic cause, or a functional suppression state.

Normal testosterone + poor semen analysis does not rule out male fertility issues. Sperm production can be impaired even when serum testosterone is not clearly low.

How Leydig Cells Affect Sperm and Fertility

Leydig cells are not sperm-producing cells, but they are still essential to male fertility. Their testosterone output helps create the right testicular environment for normal spermatogenesis. If Leydig cell function is reduced, sperm production may also decline, especially if the testosterone level inside the testes drops.

Ways impaired Leydig cell function may affect fertility

Reduced intratesticular testosterone needed for sperm development
Lower sperm count in some men
Impaired sperm maturation and quality
Reduced libido and sexual frequency, which can indirectly affect conception chances
Association with broader testicular dysfunction affecting both hormones and sperm

This is especially important for men considering testosterone replacement therapy (TRT). External testosterone can suppress LH, which reduces Leydig cell stimulation and lowers intratesticular testosterone. As a result, sperm production may drop significantly, sometimes to azoospermia.

Important fertility point

If a man wants to preserve or improve fertility, he should not assume testosterone treatment is the best first step for low testosterone symptoms. Fertility-oriented approaches may involve identifying the underlying cause and, in selected cases, using medications that stimulate the body’s own hormone production instead of shutting it down.

Treatment and Management

Treatment depends on why Leydig cell function is impaired, how severe the problem is, and whether fertility is currently a goal. Management may range from observation and lifestyle changes to hormone-based treatment, fertility medications, or treatment of underlying disease.

Common treatment approaches

Treat the underlying cause
Examples include addressing obesity, sleep apnea, medication effects, pituitary disease, testicular inflammation, or varicocele when clinically appropriate.
Fertility-preserving medical therapy
In selected men, doctors may use therapies such as hCG or selective estrogen receptor modulators to support endogenous testosterone production. Suitability depends on the diagnosis.
Testosterone replacement therapy
TRT may improve symptoms in men with confirmed hypogonadism, but it can suppress sperm production and is generally not the first choice if pregnancy is desired.
Assisted reproductive techniques
If semen parameters are significantly affected, couples may ultimately need fertility treatments such as IUI, IVF, or ICSI depending on the situation.
Monitoring over time
Some men need repeat hormone testing, semen analysis, or imaging depending on the cause and treatment plan.

When testosterone therapy may not be the right move

You are trying to conceive now or in the near future
The cause of low testosterone has not been fully evaluated
The issue may be reversible, such as obesity, sleep deprivation, or medication-related suppression
There is concern for pituitary disease or another underlying endocrine disorder

How to Support Healthy Testosterone Production

You cannot directly “target” Leydig cells with a supplement in any proven way, but you can support the hormonal system they depend on. Lifestyle changes are not a cure for every case, especially when there is true primary testicular damage, but they can make a meaningful difference in some men.

Evidence-based habits that may help overall hormone health

Maintain a healthy weight: excess body fat can negatively affect testosterone regulation.
Prioritize sleep: poor sleep can reduce testosterone production.
Exercise regularly: especially resistance training and consistent physical activity.
Limit excessive alcohol use: heavy alcohol intake may impair testicular and hormonal function.
Review medications: some opioids, steroids, and other drugs may affect hormone levels.
Manage chronic conditions: diabetes, sleep apnea, and metabolic syndrome can all influence the HPG axis.
Avoid non-prescribed anabolic steroids: they can significantly suppress natural hormone production and fertility.
Eat an adequate, balanced diet: severe caloric restriction or malnutrition can disrupt hormones.

Supplements marketed for “testosterone boosting” are often oversold. Some may be unnecessary, some may have limited evidence, and a few may even contain undisclosed ingredients. Men with symptoms should focus on proper evaluation rather than self-treating blindly.

Questions to Ask Your Doctor

If you are concerned about low testosterone, fertility, or testicular function, these questions can help guide the conversation:

Do my symptoms suggest low testosterone, infertility, or both?
Should I repeat my testosterone test in the morning?
What do my LH and FSH levels suggest about where the problem is coming from?
Do I need a semen analysis?
Could any medications, supplements, or anabolic steroids be affecting my hormones?
If I want children, would testosterone therapy hurt my fertility?
Should I be evaluated for pituitary disease, varicocele, or a genetic condition?
Are there treatment options that support testosterone without suppressing sperm production?

Common Myths About Leydig Cells

Myth: Leydig cells make sperm.

Reality: Leydig cells make testosterone. Sperm are produced from germ cells with support from Sertoli cells.

Myth: If testosterone is low, the problem is always in the testicles.

Reality: Low testosterone can come from the testes, the pituitary, the hypothalamus, medications, obesity, illness, or a combination of factors.

Myth: Taking testosterone always improves fertility.

Reality: Exogenous testosterone often suppresses sperm production and may worsen fertility while it is being used.

Myth: Normal testosterone means fertility must be normal.

Reality: A man can have normal blood testosterone and still have low sperm count, poor motility, or other fertility issues.

Myth: Over-the-counter testosterone boosters can fix Leydig cell problems.

Reality: Many supplements have weak evidence or uncertain quality. Persistent symptoms deserve proper medical assessment.

Frequently Asked Questions

What are Leydig cells in simple terms?

Leydig cells are hormone-producing cells in the testicles. Their main job is to make testosterone.

Where are Leydig cells located?

They are found in the spaces between the seminiferous tubules in the testes, not inside the tubules where sperm develop.

Do Leydig cells produce sperm?

No. Leydig cells produce testosterone. Sperm production happens in the seminiferous tubules with support from Sertoli cells.

What hormone stimulates Leydig cells?

Luteinizing hormone, or LH, from the pituitary gland stimulates Leydig cells to make testosterone.

What happens if Leydig cells are damaged?

Testosterone production may fall. Depending on severity, this can affect libido, energy, erections, mood, body composition, and fertility.

Can Leydig cell problems cause infertility?

Yes. Reduced testosterone production inside the testes can impair the environment needed for normal sperm production.

How do doctors test Leydig cell function?

Usually through blood hormone testing, especially testosterone and LH, along with symptoms and sometimes semen analysis if fertility is a concern.

Are Leydig cells the same as Sertoli cells?

No. Leydig cells make testosterone, while Sertoli cells support developing sperm.

Does age affect Leydig cells?

Yes. With age, Leydig cells may become less responsive, and testosterone production can decline, though the degree varies widely between men.

Can Leydig cells recover after steroid use?

Sometimes, but recovery is variable. Some men regain hormonal function over time after stopping anabolic steroids or testosterone, while others need medical evaluation and support.

At-a-Glance Summary

Leydig cells are the testosterone-producing cells of the testes. They are stimulated by LH from the pituitary and help regulate sexual development, libido, energy, muscle and bone health, and fertility. When Leydig cell function is impaired, men may develop low testosterone symptoms and reproductive issues. Evaluation usually includes hormone testing and, when fertility is relevant, semen analysis. Treatment depends on the underlying cause and whether preserving fertility is a priority.

References

Endocrine Society. Clinical practice guideline on testosterone therapy in men with hypogonadism.
American Urological Association (AUA). Guideline on the evaluation and management of testosterone deficiency.
American Society for Reproductive Medicine (ASRM). Guidance on male infertility evaluation and management.
NIDDK. Hypogonadism in men and related endocrine information.
Merck Manual Professional Edition. Male hypogonadism and testicular function overview.
StatPearls. Physiology and pathology of Leydig cells, male hypogonadism, and spermatogenesis.
Relevant peer-reviewed reviews in journals such as Endocrine Reviews, Human Reproduction Update, and Fertility and Sterility on testicular steroidogenesis and male reproductive endocrinology.