Scientists don’t know what’s causing men’s fertility to decline. But there are clues.

On YouTube, an influencer with millions of followers diagnoses the cause of declining male fertility: cell phones, especially when carried in a front pocket. A biohacker with over a million Instagram followers speculates that “infertility is massively being caused by electric vehicles.” Videos like these have millions of views and likes, giving the impression that male fertility is experiencing a crisis created by modern technologies and that improving fertility is as simple as moving a cell phone or avoiding a battery. The reality, however, is more complicated (current studies show no link between cell phones or electric vehicles and declining fertility).  

While experts generally agree that male fertility is on the decline, urologists and epidemiologists don’t agree on why it’s declining. It’s also not clear, experts emphasize, that declining male fertility is reason for concern, let alone the crisis that’s depicted on social media. Extant studies point to several potential causes, including better screening methods, environmental impacts from heat exposure, and lifestyle choices like alcohol consumption and obesity.  

But on social media, experts’ measured approach to male fertility is unheeded, and the decline is a full-blown crisis with a range of causes. In truth, the science is far more complicated.  

What’s the deal with sperm counts? 

Fertility trend discussions can be confusing, but context is key. In a urologist’s office, male fertility is an individual man’s ability to conceive. When demographers and governments refer to the fertility rate, they are calculating the number of babies born compared to women of child-bearing age—a calculation that doesn’t factor individual fertility or an individual’s desire to have children.  

Overall fertility, or the number of babies born, has fallen. Allan Pacey, deputy dean of the Faculty of Biology, Medicine and Health at the University of Manchester, has studied male reproductive health for over 30 years. He points to mundane reasons for the fertility decline: an increased use of contraception, men waiting longer to have children, and more men choosing to forgo fatherhood.   

Sperm count and quality, however, are affected by different factors, and in conversations about fertility, especially online, sperm count and overall fertility are often conflated. The studies on sperm count and quality can be harder to parse since there are conflicting results. The field’s failure to “convince people that this is an important question,” is part of the problem, Pacey says. “And therefore, we’re left hanging, not knowing what is right and what is wrong.” He speculates that the decline in male fertility ​​is the result of increased precision in sperm analysis.   

“As you improve counting methods, you get lower values, because bad techniques always overestimate the number,” he explains. He argues that sperm counts aren’t declining; we’ve just “changed our spectacles,” as technology, training, and quality control have improved.  

A widely reported 2017 meta-analysis published in Oxford Journals: Human Reproduction Update ​still fuels much of the current conversation around male fertility. The paper found that sperm counts in Western countries have declined by almost 60 percent on a global level since 1973. The 2023 update by the same authors reiterated this finding, plus a decline in South and Central America, Africa, and Asia. Epidemiologist Hagai Levine, the study’s lead author, warned that left uninterrupted, the trend could lead to human extinction.  

“This is the canary in the coal mine,” Levine says. “It signifies that something is very wrong with our current environment, as lower sperm counts predict morbidity and mortality.”   

Though Levine’s warning may sound ominous, it’s been contradicted by other retrospective studies. In 2025, the Cleveland Clinic said there was no cause for panic after a systematic review it published found sperm counts to be steady. That review analyzed studies published in the past 53 years. “There is no evidence to suggest that this decline is the cause of a precipitous decline in the ability to cause pregnancies,” says Scott Lundy, a reproductive urologist at the Cleveland Clinic and the primary author of the study. “Most men, even with a modest decline in sperm counts, will still have no issues conceiving.”  

Despite these findings, the prevalence of male factor infertility, or an inability to conceive, must be recognized, Lundy says. One in six couples in the world is infertile, and of those couples, around half have a male factor. But there is no evidence to suggest that any observed decline in sperm counts is leading to a dramatic decline in the ability to conceive.   

A 2023 meta-analysis published in Andrology found no meaningful change in sperm rates in Western European countries and the United States between 1993 and 2018. The findings, however, didn’t grip the public as Levine’s study did, nor were they widely publicized.​ 

​Much of the evidence for a male fertility crisis rests on retrospective studies, Pacey says, where preexisting data from disparate sources are combined and analyzed before researchers attempt to “draw a line” to establish a trend. According to Pacey, it’s an “inherently flawed” approach that requires making assumptions about the data.   

 Prospective studies on sperm counts are rarer—and more expensive since they require following participants over an often long period of time, instead of analyzing preexisting data. ​​But they exist. Researchers in Denmark conducted a prospective study in 6,000 young men in 2018 and found no meaningful change in sperm count. More prospective studies are needed, Pacey says, because they would allow more insight into the scale and causes of sperm count declines.   

“Unfortunately, our field in general is plagued by low-quality data,” Lundy says. “Part of my job in life is to do more high-quality studies to answer these questions. Because not having the answers is frustrating for us.”  

How bad are microplastics, smoking, and cell phones?  

Lifestyle factors, like smoking, heavy drinking, and marijuana use, contribute to declining fertility. When a patient is a smoker, Lundy can identify cells present in his semen sample that are a direct result of smoke-induced inflammation. Doctors often recommend lifestyle changes—such as quitting smoking, exercising, losing weight, and reducing alcohol—to improve fertility. There are, of course, other factors that contribute to fertility decline, including environmental ones, but as with many studies in the field, the results vary.   

Microplastics are often cited on social media because they have even been found in testicles, but it’s unclear what, if any, effects they have. Lundy is less concerned with these studies, describing them as “methodologically limited.” Recently, the studies showing microplastics in the human body, including the testicles, have been called into question in light of concern over false positives.   

There is much more evidence for endocrine-disrupting chemicals (EDCs) altering male fertility, Lundy says. These substances, found in many reusable plastics and disposable products, are associated with unhealthy sperm characteristics. The mechanisms and scale of EDCs’ impact on reproductive health are currently being studied.   

Ultimately, the environmental and genetic factors “add together in a synergistic way” that affects fertility, Lundy says.   

Some of the same influencers who warn about the sperm-reducing risk of cell phones often tout the benefits of testosterone replacement therapy (TRT). While TRT can effectively treat a host of symptoms, including sexual dysfunction, men increasingly access it via direct-to-consumer providers who don’t always disclose the treatment’s effect on men’s fertility.   

Men on testosterone typically have zero sperm counts, Lundy says. Most men on medically prescribed TRT, monitored by a physician, can recover some or most of their sperm production if they stop treatment, Lundy says, but it may never reach the level it was before TRT.   

Some doctors aren’t aware of testosterone’s impact on fertility. A 2012 survey of urologists found that 25 percent would prescribe testosterone to an infertile male patient trying to conceive with his partner. “Whether they didn’t read the survey carefully, or whether they’re misinformed, we don’t know. But to have a urologist say that is profound and certainly problematic,” Lundy says.   

“As the experts, we have to do a better job of conveying the right information and figuring out how we can disseminate this to a better degree to both providers and patients,” he says.   

(Steroid use is widespread—and it's increasingly dangerous.)

Debunking infertility myths  

Some common exposures linked with fertility issues aren’t proven. “The cell phone in the pocket is a common example,” Lundy says. It’s possible that it does affect fertility, but no data yet support the claim. The most common hindrances to male fertility are simple: lacking a healthy weight and lifestyle. Lundy believes there is a subtle decline in sperm counts that has occurred over time, which reflects “our worsening overall health as a global society.”  
 
Similarly, “systemic inflammation, infection, or disease can have a big, profound effect on the current status of fertility,” Lundy says. A man who recently had a fever from flu or COVID, for example, will have a drastically lower sperm count for three months—roughly the amount of time it takes to produce new sperm. During the fever, the body’s temperature rises, including the testicles, which can alter sperm production.   

“Sometimes we’ll see men who recently had the flu, and they’re worried about their fertility, and they get a count that shows poor semen parameters,” Lundy says. “We check them three months later, and they’re fine.”  

(Here are 5 myths about male fertility.)

Stigma and solutions   

For many men, fertility concerns can be hard to articulate. “We essentially disincentivize men to share these concerns and suggest that they bottle up their emotions and feelings,” says Lundy. Paradoxically, he notes, stress can negatively affect fertility. But there are proven ways to assess and address male infertility.   

Having a conversation with a urologist about fertility can be daunting for two reasons: First, it’s difficult to see someone like Lundy—there aren’t many reproductive urologists with specialty training in the United States—and, second, male factor infertility still carries an intense stigma.   

Instead, men will turn to the internet for a virtual workup or to a mail-order semen test. Lundy does see value in these options, as they can start the conversation. While mail-order semen tests and other at-home options offer privacy and quick results, they do not capture the exhaustive list of sperm health factors that a urologist would assess.   

For men suffering from infertility, several treatments are available. Human chorionic gonadotropin (HCG) is an injection that can “trick” the testicle into making sperm, which can restore a degree of fertility to patients on TRT or with certain medical conditions like hypergonadotropic hypogonadism. Selective estrogen receptor modulators (SERMs), an oral medication used to treat breast cancer, are often used off label to treat male infertility and low testosterone production, or hypogonadism.  

Aromatase inhibitors, also developed to treat breast cancer, are another oral medication used to improve men’s fertility. There is a roughly 10 percent chance that aromatase inhibitors can cause a puzzling decline in fertility, Lundy warns, and it’s currently impossible to predict who will have this reaction. That’s why it’s important for men using these medications to have close medical supervision.   

 A common surgical option is varicocelectomy, which Lundy says he performs hundreds of times every year. When a set of veins above the testicle, usually on the left, becomes dilated during puberty, it is called a varicocele. About 15 percent of all men have one, and many do not have any symptoms from it. But it can cause infertility, and some men do not realize they have a varicocele until they have issues conceiving. In 2024, Lundy and his team improved a couple’s fertility by around a hundredfold with a bilateral varicocele repair, resulting in a healthy baby.   

“We do have a number of options,” Lundy says. “I think all of us wish we had more tools in that toolbox, but we do have the ability to help many men who come and see us.”