About one in six couples worldwide struggles to conceive, and male factors play a role in roughly half of those cases. The most common causes of male infertility involve problems with sperm production, sperm transport, or sperm function. Hormone disorders, genetic conditions, varicoceles, infections, and lifestyle exposures can all contribute. In many men, more than one factor is at work, and in a meaningful share of cases, no clear cause is ever found.
What Causes Men To Be Infertile Common Factors?
Male fertility depends on a long chain of events working correctly. The brain must signal the testes. The testes must produce testosterone and sperm. The sperm must mature, travel through a series of ducts, and mix with seminal fluid. Any break in that chain can reduce fertility.
Doctors group the causes into a few broad categories:
- Sperm production problems — the testes make too few sperm, sperm with poor shape, or sperm that move poorly
- Sperm transport problems — blockages or missing ducts prevent sperm from reaching the ejaculate
- Hormone disorders — the pituitary or hypothalamus fails to send proper signals to the testes
- Genetic causes — chromosomal or gene abnormalities affect sperm development
- Environmental and lifestyle factors — heat, toxins, medications, and other exposures
Sperm production problems are by far the most common. The testes are temperature-sensitive, and sperm development takes about 74 days from start to finish. That long timeline means anything that disrupts the process can take weeks or months to show up in a semen analysis — and equally long to recover from if the trigger is removed.
How Common Is Male Infertility?
Male factors contribute to about half of all infertility cases, either alone or alongside female factors. In roughly 30 percent of couples, the male partner is the sole cause. Another 20 percent or so have a mix of male and female factors.
These numbers come from decades of clinical data. They have been stable across studies in different countries, which suggests the underlying biology is consistent even as environments and lifestyles change.
It is worth separating two ideas. Infertility means a couple has not conceived after 12 months of regular unprotected sex. Subfertility means reduced fertility that may still allow natural conception, just more slowly. Many men labeled infertile are actually subfertile. Sperm counts low enough to delay conception are not always low enough to prevent it.
What Sperm Problems Cause Male Infertility?
Semen analysis measures three main things: count, movement, and shape. Problems in any of these can reduce fertility.
Low sperm count (oligospermia) means fewer than 15 million sperm per milliliter. Poor motility (asthenospermia) means fewer than 40 percent of sperm are moving properly. Abnormal shape (teratospermia) means fewer than 4 percent of sperm have a normal form. These thresholds come from World Health Organization reference values and represent the lower end of what is seen in men who have fathered children — not a strict cutoff between fertile and infertile.
That distinction matters. Some men with counts below these thresholds conceive naturally. Some with normal counts do not. Semen analysis is a snapshot, not a verdict, and it varies between samples. Doctors usually want at least two analyses spaced weeks apart before drawing conclusions.
Azoospermia — no sperm in the ejaculate at all — affects a smaller share of infertile men. It can be obstructive, meaning sperm are made but blocked, or non-obstructive, meaning production itself has failed. The distinction changes what treatments are possible.
Can Hormones Cause Male Infertility?
Yes, though hormone problems are less common than sperm production issues. The pituitary gland releases two hormones — luteinizing hormone (LH) and follicle-stimulating hormone (FSH) — that tell the testes to make testosterone and sperm. If the pituitary or the hypothalamus above it malfunctions, sperm production falls.
This pattern is called hypogonadotropic hypogonadism. It can result from:
- Pituitary tumors or damage from radiation
- Anabolic steroid use, which suppresses the brain’s signals to the testes
- Severe weight loss, extreme exercise, or eating disorders
- Certain medications, including some opioids
- Rare genetic conditions such as Kallmann syndrome
Anabolic steroid use deserves specific mention. These drugs shut down sperm production by suppressing LH and FSH. The effect is often reversible, but recovery can take months to years, and some men do not fully recover. This is well documented in the medical literature.
High prolactin levels, thyroid disorders, and excess estrogen can also interfere with sperm production, though the evidence for each varies in strength.
What Role Do Genetics Play?
Genetic causes account for a meaningful share of severe male infertility. Two are especially well known.
Klinefelter syndrome occurs when a man has an extra X chromosome (XXY instead of XY). It affects roughly 1 in 500 to 1 in 1,000 male births and usually causes small testes, low testosterone, and very low or absent sperm production. Many men with Klinefelter syndrome are not diagnosed until they seek fertility testing.
Y chromosome microdeletions are small missing pieces of the Y chromosome that control sperm production. They are found in a notable fraction of men with very low or zero sperm counts. Testing for these matters because the deletion can be passed to sons conceived through assisted reproduction.
Other genetic causes include cystic fibrosis gene mutations (which can cause absent or blocked vas deferens), karyotype abnormalities, and rare single-gene disorders. A genetic evaluation is usually recommended when sperm counts are severely low or absent.
Can Varicoceles Cause Infertility?
A varicocele is an enlarged vein in the scrotum, similar to a varicose vein in the leg. It is found in about 15 percent of all men but in roughly 40 percent of men being evaluated for infertility. This association has been recognized for decades.
The mechanism is thought to involve increased scrotal temperature and reduced blood flow, both of which can impair sperm production. However, the picture is not simple. Many men with varicoceles have normal fertility. Many men without them are infertile. A varicocele is a finding, not automatically a cause.
Whether repairing a varicocele improves fertility remains debated. Some studies show improvement in sperm parameters after surgery. Others show no clear benefit in pregnancy rates. Clinical guidelines vary on when repair is appropriate. This is a case where the evidence is genuinely mixed, and the decision usually depends on the individual situation.
What Lifestyle and Environmental Factors Matter?
Several exposures have consistent evidence linking them to reduced sperm quality.
Heat. The testes sit outside the body because sperm production works best a few degrees below core body temperature. Frequent hot tub use, prolonged laptop placement on the lap, and tight clothing have all been studied. The effects are usually temporary, but they are real.
Smoking. Research consistently shows that smoking reduces sperm count, motility, and normal shape. It also damages sperm DNA. The effect generally scales with how much a man smokes.
Alcohol. Heavy drinking suppresses testosterone and sperm production. Moderate drinking has less clear effects, and studies on light drinking are inconsistent.
Obesity. Excess body fat alters hormone balance, raising estrogen and lowering testosterone. Obesity is associated with lower sperm counts in many studies, though the effect size varies.
Environmental toxins. Pesticides, heavy metals, and some industrial chemicals have been linked to sperm damage, particularly with occupational exposure. Evidence in this area is growing but often limited by study design.
Medications. Some prescription drugs affect fertility, including certain antidepressants, chemotherapy agents, and testosterone replacement therapy. Testosterone therapy in particular suppresses sperm production — a fact many men are not told before starting it.
Cell phones and radiation. This gets a lot of attention. The evidence so far is weak and inconsistent. Some studies suggest a possible effect from keeping a phone in a front pocket, but the findings are not strong enough to draw firm conclusions.
What Causes Infertility When No Cause Is Found?
In a substantial number of cases — often cited as around 30 to 40 percent of male infertility evaluations — no specific cause is identified. This is called idiopathic infertility.
That does not mean nothing is wrong. It means current tests cannot pinpoint the problem. Standard semen analysis looks at count, movement, and shape, but says little about sperm DNA integrity, oxidative stress, or the many molecular steps involved in fertilization. Research is slowly filling these gaps, but clinical testing lags behind.
For couples in this situation, the honest position is that the cause is unknown, not that there is no cause. Treatment often focuses on assisted reproduction rather than fixing an underlying problem.
When Should a Man Get Evaluated?
Guidelines generally recommend evaluation after 12 months of trying to conceive without success. Earlier evaluation is warranted if there is a known risk factor — prior testicular surgery, chemotherapy, a history of undescended testes, or a family history of fertility problems.
Evaluation typically starts with a medical history, physical exam, and at least one semen analysis. Hormone testing and genetic testing follow if indicated. A urologist or reproductive endocrinologist usually handles the workup.
Many causes of male infertility are treatable, and some are reversible. Others are not, but even then, assisted reproduction offers options. The key is getting an accurate diagnosis rather than assuming the problem is permanent.
Frequently Asked Questions
What is the most common cause of male infertility?
Sperm production problems are the most common cause, meaning the testes make too few sperm, sperm with poor movement, or sperm with abnormal shape. These issues account for the majority of male factor cases.
Can male infertility be reversed?
Some causes are reversible, including hormone imbalances, medication effects, and lifestyle-related sperm damage. Others, such as genetic conditions or permanent blockages, are not reversible but may still be addressed through assisted reproduction.
Does masturbation cause male infertility?
No. Masturbation does not cause infertility. It temporarily lowers sperm count in the next ejaculation, but the body replenishes sperm continuously, and there is no evidence it harms long-term fertility.
How long does it take to improve sperm quality?
Sperm development takes about 74 days, so changes from lifestyle adjustments or treatment typically take two to three months to appear on a semen analysis. Some improvements may take longer.
