Why Are Some Men Infertile? Causes And Diagnosis

Male infertility is more common than most people think. It plays a role in roughly half of all cases where couples struggle to conceive. The causes range from low sperm count and poor sperm movement to blockages, hormone problems, and genetic conditions. Diagnosis always starts with a semen analysis, but finding the root cause often requires blood tests, physical exams, and sometimes genetic screening. The good news is that many causes are treatable, and assisted reproduction options exist even when the underlying issue cannot be fixed.

What Counts as Male Infertility?

Infertility is defined as the inability to conceive after one year of regular, unprotected sex. For couples where the woman is over 35, that timeline drops to six months. When a couple cannot conceive, the man is a contributing factor in about 50 percent of cases.

Male infertility is not a single condition. It is an umbrella term covering problems with sperm production, sperm quality, sperm delivery, or a combination of these. A man can have a normal sperm count but poor movement. Another man may produce no sperm at all. Both are forms of male infertility with very different causes and treatments.

Why Are Some Men Infertile Causes And Diagnosis

The causes of male infertility fall into three broad categories: problems making sperm, problems with sperm function, and problems delivering sperm. Within those categories are dozens of specific conditions.

Low sperm count (oligospermia) and no sperm in the ejaculate (azoospermia) are the most common findings. Sperm may also be misshapen (abnormal morphology) or unable to swim properly (poor motility). Any of these can prevent fertilization.

Hormonal problems matter too. The brain and testes communicate through hormones like follicle-stimulating hormone (FSH) and luteinizing hormone (LH). If that signaling breaks down, the testes may not receive the message to produce sperm. Conditions like hypogonadism, where the testes do not produce enough testosterone, directly affect fertility.

Physical blockages are another cause. A past infection, injury, or a vasectomy can block the tubes that carry sperm. In these cases, sperm production may be perfectly normal, but the sperm never reach the ejaculate.

Genetic conditions account for a small but important percentage of cases. Klinefelter syndrome, where a man has an extra X chromosome, causes small testes and little or no sperm production. Microdeletions on the Y chromosome can also impair sperm production. These are not fixable, but they are diagnosable with a simple blood test.

Lifestyle Factors That Affect Sperm Health

Lifestyle choices do not cause infertility in the way a genetic condition does, but they can push a man from fertile to subfertile. The evidence here is strong for several factors.

Smoking tobacco consistently shows up in studies as harmful to sperm count and DNA quality. Heavy alcohol use lowers testosterone and impairs sperm production. Using anabolic steroids shuts down the body’s own testosterone production, often causing sperm counts to drop to zero. This is usually reversible if the steroids are stopped, but recovery can take months.

Heat is a real factor. The testes sit outside the body because sperm production requires a temperature slightly cooler than core body temperature. Frequent sauna use, hot tubs, or wearing tight underwear for long periods can temporarily lower sperm counts. The effect is reversible once heat exposure stops.

Body weight matters. Obesity is linked to lower sperm counts and hormonal changes that impair fertility. Weight loss in obese men has been shown to improve sperm parameters in some studies.

Stress does not directly cause infertility, but it can reduce sexual function and libido, which makes conception less likely. Sleep deprivation and poor diet have also been associated with lower sperm quality, though the evidence is less definitive than for smoking or steroid use.

Medical Conditions That Cause Infertility

Several medical conditions directly affect male fertility. Varicocele is the most common correctable cause. It is a varicose vein in the scrotum that raises testicular temperature and impairs sperm production. It is found in about 15 percent of all men but in roughly 40 percent of men being evaluated for infertility. Surgical repair is an option, though the evidence on how much it improves pregnancy rates is mixed.

Infections can cause infertility in two ways. Sexually transmitted infections like chlamydia and gonorrhea can cause scarring that blocks sperm transport. Other infections, like mumps after puberty, can directly damage the testes. A history of epididymitis, an inflammation of the tube that stores sperm, also raises risk.

Cancer and its treatments are significant causes. Chemotherapy and radiation can permanently damage sperm-producing cells. Many men choose to bank sperm before starting cancer treatment. Testicular cancer itself can impair fertility, even before treatment begins.

Certain medications have known fertility effects. Some blood pressure medications, antidepressants, and drugs used to treat prostate enlargement can impair ejaculation or sperm function. If a man is taking one of these and trying to conceive, a conversation with his doctor about alternatives is reasonable.

How Male Infertility Is Diagnosed

Diagnosis begins with a medical history and physical exam. The doctor will ask about past infections, surgeries, medications, and lifestyle habits. The physical exam checks for varicoceles, testicular size, and the presence of the vas deferens, the tube that carries sperm.

The semen analysis is the cornerstone of diagnosis. It measures sperm count, movement, and shape. According to World Health Organization reference values, a normal sperm count is 15 million sperm per milliliter or more. Total sperm count should be at least 39 million per ejaculate. Movement and shape have their own thresholds. A single abnormal result is not enough for diagnosis. Because sperm counts fluctuate, two or three analyses are usually needed over several weeks.

If the semen analysis is abnormal, further testing follows. Blood tests check hormone levels, including testosterone, FSH, and LH. These results help determine whether the problem is in the testes themselves or in the signaling from the brain.

Genetic testing is recommended when sperm counts are extremely low or zero. The two main tests are a karyotype, which counts the chromosomes, and a test for Y-chromosome microdeletions. These tests matter because the results can affect not just the man’s fertility but also the health of any children conceived through assisted reproduction.

Imaging may be used in specific situations. An ultrasound of the scrotum can confirm a varicocele or detect blockages. A transrectal ultrasound can check for blockages in the ejaculatory ducts.

Treatments Based on the Cause

Treatment depends entirely on the cause. For a varicocele, surgery may improve sperm parameters. For a hormonal deficiency, medication can sometimes restore sperm production. For a blockage, surgery may be able to bypass or repair the obstruction.

When the cause is not correctable, assisted reproduction is the path forward. Intrauterine insemination (IUI) places washed sperm directly into the uterus. In vitro fertilization (IVF) combines sperm and egg in a lab. Intracytoplasmic sperm injection (ICSI), where a single sperm is injected directly into an egg, has made it possible for men with very low sperm counts to father biological children.

For men with no sperm in the ejaculate, surgical sperm retrieval is an option. Sperm can be extracted directly from the testicles or epididymis in a minor procedure. This works when the testes are producing sperm but the sperm cannot get out. It does not work when the testes are not producing sperm at all.

Lifestyle changes are worth making regardless of the cause. Quitting smoking, limiting alcohol, stopping anabolic steroids, and losing weight if overweight are all reasonable steps. They may improve sperm quality, and they carry no downsides.

When to See a Doctor

A man should see a doctor if he and his partner have been trying to conceive for one year without success, or six months if the partner is over 35. Earlier evaluation is warranted if there is a known risk factor, such as a history of testicular surgery, undescended testicles, cancer treatment, or a known genetic condition.

It is also worth seeing a doctor for specific symptoms. Pain, swelling, or a lump in the testicles should never wait. Problems with ejaculation, low sex drive, or erectile dysfunction also warrant a conversation with a healthcare provider.

Male infertility is not a verdict. It is a medical condition with identifiable causes and multiple treatment paths. The first step is the hardest but also the most important: getting evaluated.