A low sperm count means fewer than 15 million sperm per milliliter of semen. A normal count ranges from 15 million to over 200 million per milliliter, so anything below that threshold is considered low. The medical term is oligospermia, and it’s one of the most common reasons couples struggle to conceive naturally.
When the count drops below 5 million per milliliter, it’s classified as severe. At that level, natural conception becomes significantly harder, though it’s not impossible. Understanding what drives the number down, and what can bring it back up, matters whether you’re actively trying for a baby or just got unexpected results on a semen analysis.
How Sperm Count Affects Fertility
Sperm count alone doesn’t tell the whole story. What matters most for conception is the total number of sperm that are both present and moving forward effectively. A total motile count above 20 million is considered normal. Below that, your chances of a successful pregnancy drop noticeably.
That said, lower counts don’t mean zero chance. Men with counts between 5 and 15 million per milliliter can still father children naturally, though it may take longer. When the total motile count is above 5 million, assisted options like intrauterine insemination or in vitro fertilization remain viable. Even men with very low counts often have enough sperm for procedures where a single sperm is injected directly into an egg.
Common Causes of Low Sperm Count
Sperm production is a long, temperature-sensitive process. Your body produces between 150 and 275 million sperm per day, and each sperm cell takes roughly 42 to 76 days to fully mature. That means anything disrupting the process over a period of weeks or months can show up as a lower count on a test.
Varicoceles
A varicocele is an enlarged vein in the scrotum, similar to a varicose vein in the leg. It’s the single most common identifiable cause of low sperm count in men evaluated for infertility. The leading explanation is heat: the dilated veins impair blood flow and raise the temperature inside the scrotum, which damages sperm production over time. Animal studies confirm that creating a varicocele leads to elevated testicular temperature and poor sperm function. In humans, varicoceles are associated with a progressive decline in both sperm output and testosterone production, meaning the longer one goes untreated, the worse the numbers tend to get.
Hormonal Imbalances
Sperm production depends on a chain of hormonal signals. The brain’s hypothalamus releases a signaling hormone that tells the pituitary gland to produce two key hormones: one that triggers testosterone production in the testes, and another that directly stimulates sperm development. If any link in that chain breaks, whether from a pituitary problem, a genetic condition, or certain medications, sperm production slows or stops entirely.
Weight
Carrying excess weight has a measurable effect. A large analysis combining data from 14 studies found that overweight men were 11 percent more likely to have a low sperm count compared to normal-weight men. For obese men, the risk jumped to 42 percent. Even more striking, obese men were 81 percent more likely to produce no sperm at all. Excess body fat disrupts the hormonal balance needed for sperm production and raises scrotal temperature through insulating tissue.
Testosterone Therapy
This one catches many men off guard. Taking external testosterone, whether prescribed for low energy or used for bodybuilding, sends a signal to the brain that the body already has enough. The brain then stops telling the testes to produce their own testosterone and sperm. Internal testosterone levels can plummet so low that sperm production shuts down almost completely. In one study of 271 men receiving weekly testosterone injections, 65 percent had zero detectable sperm after six months. The average time to reach that point was about four months. This effect is usually reversible after stopping, but recovery can take many months.
Other Contributing Factors
- Heat exposure: Frequent hot tub or sauna use, prolonged laptop use on the lap, or occupations involving high heat can suppress production.
- Infections: Certain sexually transmitted infections or other reproductive tract infections can damage sperm-producing tissue or block the tubes sperm travel through.
- Medications: Some antibiotics, antifungals, ulcer medications, and chemotherapy drugs interfere with sperm production.
- Substance use: Heavy alcohol consumption, smoking, and cannabis use are all linked to reduced sperm counts.
- Stress and sleep deprivation: Chronic stress raises cortisol, which suppresses the reproductive hormone chain.
How a Semen Analysis Works
The test itself is straightforward. You provide a semen sample, typically through masturbation, either at a clinic or at home with a sterile collection cup. Before the test, you should avoid any sexual activity that causes ejaculation for 2 to 3 days. Going shorter than that can dilute the count, and waiting longer than 5 days can reduce sperm quality. If you collect at home, the sample needs to reach the lab within 30 minutes, and a specialist must examine it within 2 hours.
Because sperm counts fluctuate naturally, a single low result doesn’t confirm a diagnosis. Most providers will repeat the test at least once, typically 2 to 4 weeks later. Given that the full sperm production cycle runs 42 to 76 days, testing again after making lifestyle changes usually means waiting at least 2 to 3 months to see whether those changes moved the needle.
What Improves Sperm Count
For lifestyle-related causes, the same production timeline that works against you also works in your favor. Since new sperm are constantly being made, changes you make today start showing up in test results within about 2 to 3 months.
Losing weight, if you’re overweight or obese, is one of the most impactful steps. Given the steep increase in risk that comes with higher BMI, even modest weight loss can improve the hormonal environment for sperm production. Quitting smoking, reducing alcohol, improving sleep, and managing stress all support the hormonal chain that drives production.
For varicoceles, a minor surgical procedure to redirect blood flow away from the dilated vein often improves sperm counts over the following 3 to 6 months. For hormonal causes, targeted hormone therapy (distinct from testosterone replacement) can restart the signaling chain without shutting down the testes. Men who developed low counts from testosterone therapy typically see gradual recovery after stopping, though it can take 6 to 12 months or longer for counts to normalize.
When natural conception remains difficult despite treatment, assisted reproduction fills the gap. The threshold for which technique is appropriate depends largely on how many motile sperm are available. Counts above 5 million total motile sperm generally open the door to less invasive options, while counts below that point toward more specialized procedures that require far fewer sperm to succeed.