A low sperm count has many possible causes, ranging from everyday habits to underlying medical conditions. The threshold most fertility specialists use is about 15 million sperm per milliliter of semen, and anything below that is considered low. Understanding the specific factors behind a reduced count is the first step toward improving it, and in many cases, the cause is something reversible.
Heat and Your Testicles
Sperm production requires a temperature at least 2°C below your core body temperature. That’s why the testicles sit outside the body in the first place. When scrotal temperature rises, even modestly, the developing sperm cells begin to die off through a process called apoptosis. The cells most vulnerable to heat damage are the ones in mid-development, meaning a few hours of overheating today can show up as a lower count weeks later.
Common triggers include tight underwear, prolonged sitting, resting a laptop on your lap, and frequent hot tub or sauna use. Scrotal temperature is lowest when the testicles hang freely and can dissipate heat. Anything that presses them close to the body or traps warmth around them works against sperm production. If your job involves long hours of sitting, or you regularly wear compression-style clothing, heat exposure is one of the first things worth addressing.
Varicoceles
A varicocele is an enlargement of the veins inside the scrotum, similar to a varicose vein in the leg. They’re found in about 15% of men overall but show up in roughly 40% of men being evaluated for infertility, making them one of the most common physical causes of low sperm count. The leading explanation is that the swollen veins impair blood flow and raise the temperature inside the scrotum, circling back to the heat problem. Varicoceles are often painless and go unnoticed until a fertility workup. Surgical repair improves sperm parameters in many cases.
Hormonal Imbalances
Sperm production depends on a chain of hormonal signals. Your brain’s hypothalamus releases a signaling hormone that tells the pituitary gland to produce two key hormones: one that triggers testosterone production in the testicles, and another that directly stimulates the cells responsible for making sperm. If any link in that chain is disrupted, sperm output drops or stops entirely.
This can happen for several reasons. Pituitary tumors, head injuries, or certain genetic conditions can reduce the brain’s hormonal output. Obesity is another major contributor because excess body fat converts testosterone into estrogen, shifting the hormonal balance away from sperm production. Even chronic stress and poor sleep can suppress the hormonal signals your testicles need.
Anabolic Steroids and Testosterone
This one catches many men off guard. Taking supplemental testosterone, whether prescribed or through anabolic steroids, signals your brain that testosterone levels are already high. Your pituitary gland responds by shutting down the hormones that drive sperm production. The result is often a sperm count that drops to near zero. This effect is usually reversible after stopping, but recovery can take many months, and in some cases counts don’t fully return to baseline.
Other Medications That Affect Sperm
Several common prescription medications can impair sperm production or quality. Antidepressants like paroxetine and bupropion, anti-seizure drugs like valproate and pregabalin, certain blood pressure medications, sedatives in the benzodiazepine class, and some cholesterol-lowering drugs have all been linked to negative effects on the testicular environment in research studies. If you’re taking any long-term medication and concerned about fertility, it’s worth discussing alternatives with your prescriber rather than stopping anything on your own.
Smoking, Alcohol, and Oxidative Stress
Sperm cells are unusually vulnerable to a type of cellular damage called oxidative stress. Their outer membranes are rich in fragile fatty acids, they carry very little internal protective machinery, and they have almost no ability to repair themselves once damaged. When harmful molecules called free radicals attack the sperm membrane, it loses its structural integrity. The sperm can’t swim properly, and its DNA may fragment.
Smoking is one of the strongest lifestyle drivers of this damage. It floods the body with free radicals and directly exposes reproductive tissue to toxins. Alcohol consumption, obesity, and even air pollution also increase oxidative stress in the reproductive system. These factors don’t just lower your count. They reduce the quality of the sperm you do produce, affecting motility and DNA integrity.
Environmental Chemicals
A growing body of evidence points to everyday chemical exposures as a contributor to declining sperm counts. Chemicals that interfere with your hormonal system are found in plastics, personal care products, pesticides, and food packaging. The ones most consistently linked to reduced sperm counts and quality include:
- BPA (bisphenol A): Found in plastic containers, receipt paper, and can linings. It blocks the action of testosterone at the cellular level and disrupts sperm development.
- Phthalates: Present in fragrances, vinyl flooring, and soft plastics. Studies of nearly 500 men found that higher phthalate exposure correlated with lower total sperm counts, reduced motility, and lower testosterone levels.
- PFAS (“forever chemicals”): Found in nonstick cookware and water-resistant fabrics. These accumulate in the body and are linked to hormonal disruption and metabolic changes that affect fertility.
- Pesticides: Certain agricultural chemicals, including the herbicide atrazine and the insecticide chlorpyrifos, reduce sperm counts and alter hormone levels in animal studies, with emerging evidence of similar effects in humans.
You can’t eliminate every exposure, but reducing plastic food storage, choosing fragrance-free products, and filtering drinking water can meaningfully lower your chemical burden over time.
Genetic Causes
Some men have a genetic explanation for low sperm count that no lifestyle change will fix. One of the better-understood causes involves small deletions on the Y chromosome in a region responsible for making proteins essential to sperm development. Depending on which segment is missing, the result can range from a reduced count to producing no mature sperm at all. These deletions are passed to male offspring conceived through assisted reproduction, which is important to know when weighing fertility treatment options.
Other genetic conditions, including Klinefelter syndrome (where a man carries an extra X chromosome), can also suppress sperm production significantly. Genetic testing is typically offered when a semen analysis shows a very low count or no sperm at all.
How a Low Sperm Count Is Diagnosed
The standard test is a semen analysis. You’ll be asked to abstain from all sexual activity for two to seven days beforehand to ensure sperm counts are at their peak. The sample is usually collected at a clinic or at home with a provided container, then analyzed for concentration, motility, and shape. Because sperm counts naturally fluctuate, most doctors will repeat the test at least once before drawing conclusions.
If results come back low, further testing might include hormone blood work, a scrotal ultrasound to check for varicoceles, or genetic testing depending on the severity.
How Long Recovery Takes
One number worth keeping in mind: it takes roughly 64 days for your body to produce a new batch of sperm from start to finish. That means any change you make today, whether quitting smoking, losing weight, switching a medication, or keeping your testicles cooler, won’t show up on a semen analysis for about two to three months. This is why fertility specialists typically recommend retesting after a full cycle of sperm production has passed.
For reversible causes like heat exposure, medication side effects, or lifestyle factors, many men see meaningful improvements within three to six months of making changes. For varicocele repair, improvement in sperm parameters often takes a similar timeline. Hormonal causes may require ongoing treatment but frequently respond well once the underlying imbalance is corrected.