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The Evidence of Women's Health

Why Is My Sperm Count So Low?

A plain-language guide to the most common causes — and what you can do about it.

A normal sperm count is 15 million per milliliter or more (WHO 2021). Below that — and especially below 10 million — it can be harder to get pregnant naturally. Low sperm count (called oligospermia) has many causes, and many of them are treatable or reversible. The first step is finding out why.

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Medications — especially finasteride (Propecia)
Finasteride, taken daily for hair loss, lowers a hormone called DHT. For some men, this disrupts the hormonal balance needed to make sperm. Sperm counts can fall dramatically — even at the low 1 mg hair-loss dose. In one study, stopping finasteride led to an average 11-fold increase in sperm count over 3 months. Mr. Stone (see NYT 2025) went from 2 million to 250 million/mL after stopping. Other medications that can lower sperm count include testosterone supplements, anabolic steroids, certain antidepressants, sulfasalazine, and some antibiotics.
Often reversible after stopping the medication
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Varicocele (enlarged veins in the scrotum)
A varicocele is like a varicose vein inside the scrotum. It raises the temperature around the testicles, which harms sperm production. Varicoceles are found in about 15% of all men and up to 40% of men being evaluated for infertility. It is the most surgically correctable cause of male infertility.
Treatable with surgery (varicocelectomy)
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Hormonal imbalance
The brain (pituitary gland) sends signals — FSH and LH — to tell the testicles to make sperm and testosterone. If those signals are too low or too high, sperm production suffers. Causes include tumors, thyroid problems, and high prolactin levels. A simple blood test can identify most hormonal causes.
Often treatable with medication
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Lifestyle factors
Heat (hot tubs, laptops on the lap, tight underwear), smoking, heavy alcohol use, marijuana, anabolic steroids, obesity, and chronic stress all reduce sperm counts. These effects are usually gradual but real. Sperm take about 74 days to develop — so changes in lifestyle take at least 3 months to show up in test results.
Often reversible with lifestyle changes
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Genetic causes
Some men are born with chromosomal differences — such as Klinefelter syndrome (XXY) or Y-chromosome microdeletions — that affect sperm production. These are not reversible, but assisted reproductive techniques (like IVF with ICSI) may still help achieve pregnancy.
Genetic testing recommended when count is very low or zero
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Past infections
Mumps orchitis (mumps infection in the testicle) can permanently damage sperm-producing cells. Sexually transmitted infections such as chlamydia and gonorrhea can cause blockages in the ducts that carry sperm. Treating an active infection helps, but scarring from old infections may require surgery or assisted reproduction.
STI screening is part of infertility workup
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Blockages (obstructive azoospermia)
Even when the testicles make sperm normally, a blocked vas deferens or epididymis can prevent sperm from reaching the semen. Causes include past vasectomy, prior surgery, infection, or congenital absence of the vas deferens (associated with cystic fibrosis gene mutations). Sperm can often be retrieved directly from the testicle for IVF.
Surgical retrieval or reversal may be possible
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Environmental exposures
Pesticides, heavy metals (lead, mercury), radiation, and industrial chemicals (phthalates, BPA) are known to reduce sperm counts. Occupational exposure in agriculture, painting, welding, and certain manufacturing industries is associated with lower counts. Avoiding known exposures and using protective equipment helps.
Occupational history is part of the fertility evaluation

✓ Good news: many causes are reversible

Sperm are constantly being produced — a full new cycle takes about 74 days (roughly 3 months). That means if the cause is removed (a medication stopped, a varicocele repaired, a lifestyle changed), sperm counts can recover significantly. Always retest at least 3 months after making any change.

When to see a urologist or fertility specialist

Sources

  1. WHO Laboratory Manual for the Examination and Processing of Human Semen, 6th ed. Geneva: World Health Organization; 2021.
  2. Samplaski MK, Lo K, Grober E, et al. Finasteride use in the male infertility population: effects on semen and hormone parameters. Fertil Steril. 2013;100(6):1542–6.
  3. Iyer SN, Bhatt DL. Varicocele and male infertility: current concepts. Nat Rev Urol. 2022;19(1):33–47.
  4. Krausz C, Riera-Escamilla A. Genetics of male infertility. Nat Rev Urol. 2018;15(6):369–384.
  5. Skakkebaek NE, Lindahl-Jacobsen R, Levine H, et al. Environmental factors in declining human fertility. Nat Rev Endocrinol. 2022;18(3):139–157.
  6. Schlegel PN, Sigman M, Collura B, et al. Diagnosis and treatment of infertility in men: AUA/ASRM guideline part I. J Urol. 2021;205(1):36–43.

This tool is for educational purposes only and does not replace evaluation by a qualified physician. If you have concerns about fertility, please speak with a urologist or reproductive endocrinologist.