What Causes Low Sperm Count? Causes, Risk Factors & Treatment

A low sperm count is a common finding during a male fertility evaluation. Although an abnormal semen analysis can be concerning, a low sperm count does not automatically mean infertility.

Many different factors can affect sperm production or prevent sperm from reaching the ejaculate — including varicocele, hormonal disorders, genetic conditions, infections, medications, previous testicular problems, and lifestyle or environmental factors. Identifying the underlying cause is important, since some causes are reversible or treatable. Because semen parameters naturally fluctuate between samples, an abnormal result is usually interpreted in the context of the complete analysis and, when appropriate, confirmed with repeat testing.

Low sperm count is generally described using two related measurements: sperm concentration (the number of sperm in each milliliter) and total sperm number (the total number in the entire ejaculate). The term oligozoospermia refers to a concentration below the laboratory’s reference range; azoospermia is a distinct condition meaning no sperm are detected in the ejaculate at all. WHO 6th-edition reference values: concentration — 16 million/mL, total sperm number — 39 million/ejaculate, progressive motility — 30%, total motility — 42%, normal morphology — 4%.

Varicocele — an enlargement of the veins surrounding the testicle — is one of the most common identifiable conditions associated with male infertility; it can be associated with reduced sperm concentration, motility, or morphology in some men through altered testicular temperature regulation, oxidative stress, and changes in testicular blood flow. Importantly, not every varicocele causes infertility, and not every varicocele requires treatment.

Normal sperm production depends on communication between the brain and the testes through the hypothalamic-pituitary-gonadal (HPG) axis. Hormonal causes of impaired sperm production include low or abnormal FSH/LH signaling, pituitary or hypothalamic disorders, certain thyroid disorders, elevated prolactin, and severe obesity or metabolic disease. Hormonal abnormalities may sometimes be treatable, so identifying the specific cause is important.

One of the most important and potentially overlooked causes of low sperm count is external testosterone use. Testosterone replacement therapy (TRT) and anabolic steroids can suppress the body’s production of LH and FSH; when this signaling decreases, the testes produce less intratesticular testosterone, which is essential for normal sperm production. This can result in severe oligozoospermia, very low sperm production, azoospermia, and testicular shrinkage. Men who want to preserve or restore fertility should discuss their reproductive goals with a specialist before starting testosterone therapy.

Cryptorchidism, or an undescended testicle, occurs when one or both testicles fail to move into the scrotum during development. Because the scrotum provides a cooler environment than the abdomen, prolonged exposure to higher temperatures can impair sperm-producing cells; the effect on fertility depends on whether one or both testicles were affected, when treatment occurred, and whether other reproductive problems are present.

Sperm can be produced normally but fail to reach the ejaculate because of a blockage in the reproductive tract. Potential causes include epididymal obstruction, ejaculatory duct obstruction, previous infections, prior surgery, congenital abnormalities, and certain genetic conditions. Obstruction may sometimes be suspected when sperm concentration is extremely low or absent despite otherwise preserved testicular function.

Certain infections affecting the reproductive or urinary tract can interfere with fertility — examples include infections involving the epididymis, testicles, prostate, or reproductive ducts; some infections cause inflammation or scarring that interferes with sperm transport. However, an abnormal semen analysis does not automatically mean an infection is present — antibiotics should only be used when there is an appropriate clinical indication.

Damage to the testes can impair sperm production: severe testicular trauma, testicular torsion, previous testicular surgery, certain forms of groin or scrotal surgery, and previous chemotherapy or radiation. The effect depends on the severity of the injury and whether one or both testes were affected. Sperm production can also be affected by chemotherapy, certain hormone-suppressing medications, exogenous testosterone, anabolic steroids, some opioids, and other medications affecting hormonal signaling; medication effects are often individual and may sometimes be reversible after the medication is stopped — but never stop a prescribed medication on your own, and discuss potential fertility effects with your doctor.

Smoking is associated with oxidative stress and poorer semen parameters in some studies, potentially reducing sperm concentration, motility, morphology, and DNA integrity; quitting smoking is beneficial for both reproductive and overall health. Heavy alcohol consumption can affect hormone production and testicular function and may negatively affect semen quality; reducing heavy or binge drinking is recommended for men trying to optimize fertility. Some recreational drugs may also affect hormones, sexual function, or sperm production.

Obesity is associated with hormonal and metabolic changes that can affect male reproductive function; excess body fat can alter testosterone and estrogen metabolism and may contribute to inflammation and oxidative stress — improving metabolic health through regular physical activity, a balanced diet, adequate sleep, and gradual weight management may support reproductive health. Sperm production is sensitive to temperature; significant or prolonged heat exposure (frequent prolonged hot-tub use, certain occupational heat exposures, repeated high-temperature environments) may temporarily impair spermatogenesis — evidence regarding everyday activities such as laptop use or underwear type is less definitive.

Diagnosis begins with a semen analysis and medical history, plus a physical examination (which may identify a varicocele, testicular asymmetry, or other abnormalities). When indicated, doctors order hormone testing (testosterone, FSH, LH, prolactin), a scrotal ultrasound (when the exam is uncertain or to evaluate a varicocele), and, for severe oligozoospermia or azoospermia, genetic testing (karyotyping, Y-chromosome microdeletion testing, CFTR testing).

Treatment depends on why the sperm count is low. For varicocele, appropriately selected men may benefit from repair (microsurgical varicocelectomy or percutaneous embolization); not every varicocele requires treatment. Some hormonal causes can be treated medically — for example, hCG and FSH for hypogonadotropic hypogonadism, or clomiphene under specialist supervision; standard TRT is generally not an appropriate fertility treatment because external testosterone suppresses sperm production. When infertility is caused by reproductive tract obstruction, treatment may involve surgical reconstruction, removal or bypass of the obstruction, sperm retrieval, and assisted reproductive techniques such as IUI, IVF, or ICSI.

Can you get pregnant with a low sperm count? Yes. A low sperm count does not mean pregnancy is impossible; the likelihood depends on sperm concentration, total sperm number, motility, morphology, duration of infertility, and the fertility of both partners.

Can low sperm count be cured? Sometimes — it depends on the underlying cause. Some causes, such as certain hormonal disorders, medication effects, or a clinically significant varicocele, may be treatable; other causes, including certain genetic or severe testicular conditions, may not be completely reversible.

Does testosterone lower sperm count? Yes. External testosterone can suppress LH and FSH production, reducing the intratesticular testosterone needed for spermatogenesis; this can cause a dramatic reduction in sperm production and, in some men, azoospermia.

When should you see a urologist or andrologist? After 12 months of trying to conceive without pregnancy (evaluation should generally begin after 6 months when the female partner is 35 or older); when a semen analysis is abnormal; if you notice testicular pain, swelling, or a mass; if you have difficulty ejaculating; if you have erectile or significant sexual-function problems; or if you have a history of undescended testicles, testicular torsion, significant testicular injury, or previous use of testosterone or anabolic steroids.