We talk a lot about eggs here at Extend Fertility: how many eggs you have, how your egg quality changes with age, and how egg freezing can help preserve your options for parenthood later in life.

But an estimated 30% of infertility cases are deemed “male-factor infertility,” meaning eggs aren’t an issue at all. So let’s dive into the “other half” of fertility—sperm health!

People with testes produce 200–300 million spermatozoa per day.

That’s approximately 1,500 per second. About 50–100 million become viable sperm daily. If that sounds like a lot, consider that a healthy person can release 80–300 million sperm per ejaculation.

As opposed to eggs, which develop in utero and stay with you your whole life, sperm are created anew each day. The process of creating mature sperm is called “spermatogenesis,” and it happens in the testes, where’s it’s controlled by several male hormones, including the hormone testosterone. Spermatogenesis takes about 2 ½ to 3 months, but since the process is happening constantly, there’s a more or less constant supply of sperm (meaning, every day there are new sperm cells beginning and also completing the process!).

Spermatogenesis begins at puberty and continues until death, so there’s no risk of “running out” of sperm, as there is with eggs—but sperm health can nonetheless be impacted by age and lifestyle factors (more on that later).

Sperm primarily contain DNA.

The sperm cell is the male sex cell, or gamete, which combines with an egg in a process known as fertilization. Sperm cells are haploid, meaning they contain half the chromosomes (23) of a typical cell (which contains 46)—the egg contains the other half. So, when a healthy sperm and healthy egg join, they create a diploid cell with 46 chromosomes.

The genetic material is housed in the head of the sperm, which measures about 0.05 millimeter or 0.002 inch—1/30 of the size of an egg. In addition to the head, a sperm is made up of mitochondria, which provide energy for the tail, and the tail itself (also known as a flagellum). The mitochondria and the tail are what provide sperm the ability to “swim” about 8 inches per hour; that’s pretty fast, considering their tiny size.

There are several characteristics to sperm that can make it healthy or unhealthy.

The fertility of sperm is determined by observing a few characteristics, including:


This refers to how many sperm are present per milliliter of semen. A healthy sperm count is 15–20 million per milliliter or more. Oligozoospermia or oligospermia refers to a low concentration of sperm in the semen, while azoospermia refers to an absence of sperm.


Motility refers to a cell or organism’s capability to move independently, meaning in this case the “swimming” motion of a sperm cell. Ideally, 40–50% or more of sperm in a given sample will be motile. Asthenozoospermia or asthenospermia refers to reduced sperm motility.


Morphology refers to the structure, size, and shape of the sperm, which allows it to penetrate an egg for fertilization. A normal morphology is smooth, oval heads and long tails. Ideally, at least 4% of sperm in a sample will have a proper morphology. Teratozoospermia or teratospermia refers to a high presence of abnormal morphology in a semen sample.

Genetic health

Like eggs, sperm can have genetic abnormalities that make them unable to create a healthy embryo. Unlike eggs, sperm’s genetic health is not solely associated with age, but may have other causes such infection, elevated body temperature (such as a high fever), or lifestyle factors (such as smoking or drug use).

These indicators of sperm health—except genetic health, more on that later!—are tested as part of a semen analysis.

Sperm health can be impacted—positively or negatively—by lifestyle factors.

We’ve talked before about the fact that eggs are tucked away inside your ovaries, affected by the aging process, but generally unaffected by the majority of the wear and tear the rest of your body weathers. Sperm are different—because they’re constantly “in production,” their health can be greatly impacted by a variety of lifestyle and medical factors. We’ve outlined a few factors with strong evidence below, but this list is by no means exhaustive.

Activity level and weight

Several studies have linked exercise frequency to an increase in sperm health and sperm count. In one small study, men who practiced “vigorous physical activities” such as cycling, running, or swimming for more than 2 hours per occasion at least 3 times per week had better sperm motility and morphology, and lower levels of dead or dying sperm in their semen samples.

It’s hypothesized that exercise may increase testosterone levels, but additionally, some of the benefits from exercise may come from shedding excess weight. Being overweight or obese has been associated in research, such as a 2017 study of over 2,300 men in China, with lower sperm count/concentration and decreased motility.

For obese people, exercise has been shown to improve sperm health. One study demonstrarted that a 16-week aerobic training program significantly improved the sperm count, motility and normal morphology of obese patients.


The impact of tobacco smoking on male fertility is more or less medical consensus. A recent meta-analysis analyzing tobacco use and sperm health in over 10,000 subjects concluded that smoking was associated with lower sperm count, higher instance of oligozoospermia (low sperm concentration), and higher levels of morphological defects.


In one study, people who drank 5 or more drinks per week—and especially those who drank more than 25 drinks per week—had lower sperm concentration, total sperm count, and percentage of sperm with normal morphology. Subjects who drank over 40 drinks per week had a 33% reduction in sperm concentration compared to those who drank 1–5 drinks per week.


Anabolic steroids are at the top of the list for drugs that affect sperm health. Steroids are associated with significantly lower levels of motile and morphologically normal sperm. While, for many steroid users, sperm health may improve within 4–12 months of stopping the drugs, some users may experience steroid-induced hypogonadism, or a shutdown of the function of the testes.

Also on the list is cocaine. Long-term cocaine use is associated with lower sperm counts and reduced motility and morphology. Marijuana, on the other hand, is a mixed bag of research. A 2015 study found that marijuana use was associated with lower sperm concentration and count, but two studies published in 2018 found that marijuana use wasn’t associated with increased instances of infertility or increased time to pregnancy, and a 2019 study actually associated marijuana with higher sperm concentrations.

Exposure to toxins

A history of toxin exposure, often as part of a patient’s occupation, has been shown to be more than twice as likely for those with oligozoospermia, asthenozoospermia, or teratozoospermia as for fertile patients. Those who work in agriculture and herbicides, plastic production, and the military have been demonstrated to have worsened sperm parameters; substances including lead, pesticides, hydrocarbons, PCBs, cadmium, diesel exhaust, petrochemicals, and solvents may all impact sperm health.

Certain medications and medical treatments

Cancer treatments such as chemotherapy and radiation are common reasons for patients to preserve eggs, sperm, or embryos, as both can affect fertility in the short or long term. Chemotherapy works by using medications called cytostatics and cytotoxins to attack fast-dividing cancer cells and kill them or prevent them from dividing. But because the medication is usually administered “systemically,” meaning through the bloodstream to the entire body, it can also attack other cells. High doses of chemotherapy can damage sperm cell production and/or affect the testicles’ ability to make testosterone, a crucial fertility hormone.

Radiation, on the other hand, involves directing high-energy rays at the cancer, in hopes of killing those cells. But by extension, this treatment can slow down or stop sperm cell production. Some patients who undergo radiation will experience a temporary drop in fertility that recovers in the years following treatment; for others who undergo higher doses of radiation, sperm production may stop permanently.

Learn more about fertility preservation before cancer treatment.

Other medications that may affect sperm health include SSRIs and similar antidepressants, alpha blockers, ketoconazole, some antibiotics, opiates, and antipsychotics.

Making changes

The good news is that, because sperm are continuously being produced, the negative effects of medications and behaviors can typically be reversed. Based on the life cycle of sperm production, once a lifestyle change has been made—such as quitting smoking—it takes about 2 ½ to 3 months for those healthier sperm to be present in a semen sample.

Age impacts sperm health, too.

The relationship between age and sperm health isn’t quite as direct and dramatic as the relationship between age and egg health, but there is evidence that pregnancy rates are somewhat lower and miscarriage rates are somewhat higher in couples with older fathers (especially for those over 40).

Sperm health parameters can be lower, too. Research demonstrates that sperm motility decreases with age; one study of healthy, non-smoking men demonstrated that motility decreased .8% per year. Age may also result in decreased sperm morphology. Studies indicate that normal sperm morphology declines .2–.9% per year, resulting in a 4–18% decrease in normal morphology over a 20-year period.

Additionally, a child’s chances of birth defects, schizophrenia, and autism all increase with their father’s age. In one report, offspring of fathers over 50 were shown to be 2.2 times more likely to have autism than offspring of fathers under 29. In another, the risk of schizophrenia increased with paternal age, and those over 45 were 2 times more likely to father children with schizophrenia. The mechanism for this effect is not fully understood yet by researchers, but it’s possible that these increased rates of illness are caused by what experts call “de novo mutations,” or a genetic alteration appearing for the first time.

Learn more about male fertility decline with age.

Sperm parameters can be tested with a semen analysis.

A semen analysis is a fairly easy and painless test that can offer a wealth of information about sperm health. Typically, the test involves providing a semen sample—collected via masturbation or via a special condom used during sex—which is then examined under a microscope. Then, a doctor or lab tech can determine the sperm count and concentration and the percentage of motile and morphologically normal sperm. A semen analysis also usually includes other factors, such as the chemistry and volume of the semen.

A semen analysis can be performed by a fertility practice or urologist’s office with an andrology lab, like ours. It can also be done at some lab companies, with a requisition from a doctor. Recently, some home-based and mail-in tests have been developed to make the whole process more comfortable. (If you use an at-home test, be aware that many only test sperm count, which as we’ve discussed is only one element of sperm health.)

Legacy is mail-in option that gives a bit more information; in addition to providing a fertility report that assesses volume, sperm count/concentration, motility, and morphology, they also provide personalized lifestyle recommendations to improve sperm health.

The one factor that can’t be tested in a semen analysis is genetic health. There’s a newer diagnostic tool called the sperm chromatin structure assay (SCSA) that can detect sperm samples with a high degree of DNA fragmentation (small breaks in the chromosomes). Although less likely, sperm with normal morphology and motility may nonetheless have DNA fragmentation—so a SCSA can identify sperm health issues that not found by any conventional semen analysis.

Sperm can be frozen, just like eggs.

As in egg freezing, the quality and health of sperm can be preserved via cryopreservation. Sperm freezing is a useful technology for a few populations, including those about to undergo cancer treatment, those about to deploy in the military, those who may be exposed to damaging toxins as part of their work, or anyone who wants to preserve the health of their sperm now for potential use later in life. Frozen sperm can also be a useful asset for couples going through fertility treatments, in the case that the male partner is unavailable on the day of insemination or in vitro fertilization.

The sperm freezing process is quicker and simpler than egg freezing. Much as in the case of a semen analysis, freezing requires a semen sample to be collected and handed over to the lab. It’s then typically prepared in a process called “sperm washing,” which isolates healthy sperm from the remainder of the seminal fluid. Finally, the sample is frozen using liquid nitrogen and stored at -196ºC. In most cases, there is no preparation required apart from a recommended 2–3 days of abstinence prior to providing a semen sample.

Once sperm is frozen, it can be stored indefinitely, with no loss in quality. Approximately 30–50% of the sperm in the original sample will survive the thaw, which is typically more than sufficient for use in an IUI or with IVF.
Sperm can be frozen at a cryobank or at a fertility practice, or via an at-home sperm freezing service like Legacy.