Health and Human Services Secretary Robert F. Kennedy Jr. has baselessly tied alleged declines in sperm counts among teenagers to a “fertility crisis” or an “explosion in infertility.”
There is very little data on sperm counts in teenagers, and there’s mixed evidence on whether they have changed over time in adults. Regardless, experts told us there isn’t reason to believe declining sperm counts are causing the falling rate of childbirths in the U.S., which has more plausible social and behavioral explanations.
On at least a dozen occasions since becoming HHS secretary, Kennedy has claimed there has been a dramatic drop in sperm counts, saying it’s evidence of a health crisis. His interest in this topic goes back nearly a decade.
“Male sperm counts, I think, in this country are down 50% for teenage males,” he said on a May 28 episode of his recently launched podcast, after introducing concerns about a “stunning” drop in the rate of childbirths. “I read the other day that teenage males today have less sperm than the average 65-year-old American man.” At a May 11 event at the White House, he discussed statistics on childbirths, while also claiming a “fertility crisis” involving falling sperm counts in teens. “This is an existential crisis for our country,” he said.
Contrary to Kennedy’s statements, there is very little data about sperm counts in teenagers in the scientific literature at all. The studies establishing sperm counts in healthy adolescents have “never been done,” Dolores Lamb, who studies male reproductive biology and urology at Children’s Mercy Kansas City, told us.
There are some studies that have found about a 50% drop in sperm counts in men over the past half century or so. Kennedy has linked to this research or coverage of it multiple times on X. HHS has previously cited these 2017 and 2023 studies to support Kennedy’s claims, although the agency did not respond to our request for comment.
But other studies have not found such declines, and comparisons to the past are complicated by inconsistencies in how sperm is counted. “I would argue that we don’t yet have consensus,” Allan Pacey, a professor of andrology at the University of Manchester, told us.
In any case, sperm declines are not likely to be a driving factor in today’s falling childbirth rates, experts said.
“Declining sperm count are expected to impact population birth rates significantly only at very advanced stage, as men have multiple opportunities to [conceive],” Dr. Hagai Levine, an epidemiologist and public health physician at Hebrew University-Hadassah School of Public Health who co-authored the studies HHS cited, told us in an email, even as he said that in his view, the “strong decline does indicate that there is a problem.”
Alison Gemmill, a reproductive epidemiologist and demographer at the University of California, Los Angeles, told us that Kennedy is erroneously conflating the falling fertility rate with a decline in people’s biological ability to conceive. The rate of childbirths has indeed fallen, she said, but it has been driven by a drop in birth among teenagers and women in their 20s.
“What’s going on with people in their teens and 20s is they’re just waiting longer to have kids, and they’re using more effective contraception, and they’re having fewer unintended or unwanted births,” she said. “So, I think the overwhelming majority of evidence points to social and behavioral changes rather than biological changes.”
Nor has there been a recent “explosion,” as Kennedy said, in infertility by its medical definition, Katherine Tierney, an assistant professor in the department of sociology at Western Michigan University, told us in an email. While the fertility rate reflects the rate of childbirths in the population, infertility refers to difficulty becoming pregnant.
“[T]he prevalence of medically-defined infertility in the U.S. has remained fairly stable over time, despite the decline in fertility, which calls into question the proposal that rising infertility is a major driver of the fertility decline,” Tierney said, based on survey data from the Centers for Disease Control and Prevention.
Uncertainty About Sperm Count Over Time
There has been controversy for decades about whether sperm counts in the population are falling.
In 1992, Danish researchers pulled together the available data and did a meta-analysis, a type of study that combines data from multiple past studies on a topic. The researchers concluded that sperm concentration had dropped by more than 40% between 1940 and 1990. (The term sperm count encompasses two related measures: sperm concentration, or the amount of sperm per milliliter of semen, and total sperm count, or the number of sperm per ejaculate.)
Shanna Swan, an environmental reproductive epidemiologist at Icahn School of Medicine at Mount Sinai, told us in an email that the 1992 study was “very strong,” adding that it was “further strengthened” by a reanalysis of the data she published five years later. She and her co-authors found an “even steeper” decline in sperm counts in the U.S. and Europe, according to the study. (Swan went on to co-author the more recent studies with Levine that showed a decline in sperm count.)
But Lamb criticized the 1992 study for including relatively little data from the early years of the covered period, among other issues, and said that the authors “assume that the data that’s published in these papers is accurate and precise.”
In fact, sperm is quite challenging to count, Lamb and Pacey told us.
During much of this study period there was little standardization of sperm counting, Pacey explained in an editorial in 2013. The World Health Organization came out with guidelines in 1980, followed by multiple revisions. But even after this, studies showed that many labs did not follow the guidelines and that there was substantial variation between labs in counts even when they all looked at the same sample.
Ejaculate is a mixture of fluids from different glands, Pacey said. “It’s a viscous fluid, so it’s very difficult to pipette,” he explained, and there are multiple steps in sperm analysis that can introduce errors.
Lamb said that people are supposed to count sperm in specialized glass chambers with a grid after diluting semen and preventing sperm from moving. But labs may instead use disposable chambers to avoid cleaning or fail to properly immobilize the sperm.
Pacey said that he chairs a U.K. advisory committee to a national sperm counting quality assurance program, and there’s still “huge variation” among labs counting the same sample. “That makes me concerned about how accurate we are when we report [sperm count] in papers.”
Pacey added that sperm counts can also vary within even the same person depending on a variety of factors, such as length of time since last ejaculation and level of sexual stimulation, complicating analyses. And Lamb said that sperm count is a genetic trait and varies geographically. “It’s just biology,” and it’s not that areas with lower sperm counts necessarily have more infertility, she said.
The 2017 and 2023 studies on sperm count from Swan and Levine looked at more recent data than the 1992 study, excluded studies reporting nonstandard methods, excluded men known to be infertile or with exposures implicated in infertility, and otherwise attempted to address prior criticisms.
Sperm counts have “declined by 50-60% between 1973 to 2018, globally, including in North America (mainly US),” Levine said.
Lamb said that the 2017 study’s rigor had improved “a little” but said it still had issues, such as those related to counting sperm.
Despite even further improvements to the 2023 study, which added new data and analyses, “poor data is still poor data,” Lamb said. She added that the authors do not take into account “methodological issues and lack of standardization for semen analysis performance and change in methods over the years.”
Another 2023 meta-analysis by different researchers looking at studies on sperm count in the U.S. and Western Europe between 1993 and 2018 did not find a significant change over this period, including when looking specifically at the U.S.
A 2025 meta-analysis by yet another group also reviewed the U.S. sperm count literature, finding what the authors called “remarkably stable” sperm counts from 1970 to 2018. The researchers generally found no change or increases in various measures of sperm count, with the exception of a decline in sperm concentration, after adjusting for region and fertility status, that was “less than half the annual decline that has been observed in previous global meta-analyses,” the authors wrote.
Pacey said that results from different meta-analyses can vary due to differences in methods and the time period and populations covered. Lamb said the 2025 paper was particularly well done, explaining that it excluded many studies that did not meet its “criteria for rigor, strong experimental design, original data, sample number, etc.”
When three different large meta-analyses are “telling you different things, I would argue we don’t have consensus,” Pacey said, adding that people like Kennedy “kind of cherry-pick the data to suit the argument that they’re making at the time.”
Regardless, Pacey said, one wouldn’t expect the level of sperm decline that studies have reported to make a major contribution to falling birth rates. “It’s still a decline from normal to normal on average,” he said.
“When we look at studies that are more well done, there is potentially evidence of a decline, especially a long-term decline,” Gemmill said of the sperm count literature. “But the main takeaway is that when we think of this measure of sperm count, it’s still at levels that we don’t think it’s going to really make an impact on people’s ability to conceive.”
A Lack of Evidence for Teen Comparisons
Kennedy has repeatedly compared today’s teenagers to older men, claiming that “the fertility of our kids is down” and that teens have half the sperm count of a 68-year-old, 65-year-old or 60-year-old man.
“We’re seeing an explosion in infertility,” he said at an event in West Virginia in March 2025, for example. “Teenagers today have 50% of the sperm count” of 68-year-old men, he added.
Despite this rhetoric, there simply aren’t data on sperm counts comparing teens from the general population to men in their 60s.
“The studies on that directly have not been done,” Lamb said, because the panels that review studies with human subjects for institutions are not going to “have parents consent for their boys to masturbate to collect semen samples” in a clinic.
Measures such as total sperm count and volume decline as men age.
There are limited data looking at sperm counts in adolescents with health problems who have given semen samples. Lamb was involved in one study that compared sperm counts in adolescents and adults who were storing sperm samples prior to cancer treatment that might damage their fertility. The study found slightly lower sperm counts in the younger age group than in the adults.
But Lamb said that this study was not meant to establish normal sperm counts for adolescents, but rather to better understand what very young patients undergoing fertility preservation might expect. “The important thing to realize is these boys were seriously ill,” she said, and their sperm counts cannot be taken as representative.
There have also been comparisons of data on sperm counts in young men being considered for military service, some of them technically teenagers, and those of somewhat older men. Researchers in Denmark — some of whom had co-authored the 1992 paper showing falling sperm counts — tracked sperm counts from young men presenting for medical examination with a median age of 19 between 1996 and 2010. They found these young adults’ sperm counts were lower than those of two groups: sperm counts collected between 1996 and 1998 from men whose partners were pregnant, and sperm counts from 1939 to 1943 in men who were part of infertile couples.
The men in the comparison groups were largely in their 20s and 30s, and not in their 60s. But the authors of the study did raise concerns about a generational decline, writing that “there is reason to be concerned about future fertility of young Danish men.” However, the study showed that sperm counts in successive groups of young men presenting for examination rose over the 15 years of the study.
“If you want to do the best study possible, you would do a prospective study where you would actively go out and recruit new cohorts of men every year of a similar age and a similar lifestyle and a similar demographic, and you would follow them over time to see whether sperm counts were declining,” Pacey said. That is what the Danish study did in looking at potential military recruits. And this didn’t show falling sperm counts, he said.
Meanwhile, he said he thought the researchers “overinterpreted” their data on young potential recruits in going back and comparing it to data collected on different groups of men. “If retrospective data is showing one thing and prospective data is showing another, that suggests we have a data problem rather than a biology problem,” he said, adding that he doesn’t think “the study is a sign of a reduction in sperm quality in young men.”
Why Are People Having Fewer Children?
Regardless of the trends in sperm counts, demographers said there are other factors that are likely leading people to have fewer children, despite Kennedy repeatedly connecting it to falling sperm count or infertility.
“We have fertility rates that are just spiraling,” he told Jesse Watters during a Fox News interview in April 2025, going on to reference a 50% drop in sperm counts. “The fertility rate is plummeting,” he said at a June 2025 press conference, again mentioning a halving of sperm counts.
“There’s no particular reason to think that physiological factors would be a big cause of [falling birth rates], when we know there’s lots of social factors that could be contributing,” Sarah Hayford, director of the Institute for Population Research at Ohio State University, told us.
She said that broadly speaking, birth rates have been falling for 150 years in high-income countries. In the U.S., there was a decline in the 1970s after the Baby Boom, followed by “pretty stable” birth rates through the early 2000s, supported by a relatively high teen birth rate compared with other high-income countries. Birth rates again declined during the Great Recession in 2007 to 2009 and, unexpectedly to demographers, continued to fall, primarily driven by declines in births to teens and young adults in their early 20s, particularly among unmarried people.
Fertility rates are measured in various ways, but one way is to estimate how many babies a woman on average would have over her lifetime using the current birth rates for various age groups of women, or what’s called the total fertility rate. By this measure, the fertility rate in 2024 fell to a low of 1.6 per woman, according to CDC data. Provisional CDC data on birth rates from 2025 indicate they continued to fall.
Kennedy has appeared to refer to these CDC statistics, as well as to Social Security Administration estimates of total fertility rates, when referring to the falling fertility rate.
“When my uncle was president, the fertility rate in this country was 3.5%,” he said at an October 2025 White House event on fertility treatment. “Today it is 1.6%.” He then claimed the average U.S. teenager has half the sperm count of a 65-year-old man.
Hayford said that there are likely multiple social and behavioral changes working together to impact birth rates since the Great Recession. For teens, she said, “it seems pretty clear that that’s about increased contraceptive use,” particularly long-acting methods such as IUDs and implants.
Meanwhile, economic and other factors have affected people’s choices around childbearing.
One possible factor is a sense of economic insecurity that never fully dissipated after the Great Recession, despite macroeconomic recovery, Hayford said. There has also been a decline in the rates at which people get married, she added.
“Global uncertainty has increased, and just general uncertainty about the future,” UCLA’s Gemmill said. ”We’ve seen study after study show that that is also tied to decisions and ambivalence about having children.”
Gemmill added that studies have shown a rise in “intensive parenting,” or the idea that people feel “they need to give a lot more or … have more resources to support raising children in the United States.” At the same time, people are experiencing economic challenges in the housing market, the price of childcare and the availability of paid family leave, she said.
There’s also a trend toward people staying in school longer and getting more education, Hayford said.
In periods where people are shifting when they have children to later in life, the total fertility rate will likely underestimate the number of children women will have by the end of their childbearing years, Hayford said, as some people might “catch up.”
At the same time, delaying childbearing does tend to lead to a lower total number of children, as people are “more likely to run into problems” with their fertility, Hayford said. People also tend to “reduce their fertility intentions as they get older” based on the other things going on in their lives, she explained.
But apart from age-related declines in the biological ability to bear children, experts pushed back against the idea that there’s been a major rise in infertility, or the rate at which people have trouble becoming pregnant.
For one thing, Hayford said, the fact that declines in the fertility rate are concentrated in unmarried people “is an indicator that it’s probably not physiological processes going on.” If there were some chemical exposure “that was reducing fertility, you would expect to see that among married people as well as among unmarried people,” she said.
Furthermore, the data that are available on infertility in the U.S. do not indicate any major rise.
It is “very hard” to measure the biological capacity for childbearing over time, Gemmill said. However, when researchers have attempted to track the rate of Americans meeting the medical definition of infertility, “there’s not really much change,” she said, referring to the CDC’s National Survey of Family Growth.
Several studies using these data have looked at the rate of infertility — defined as no pregnancy following 12 months of regular, unprotected intercourse — among married and cohabiting women. The studies found no significant change between 1995 and 2019 or, in one case, a small rise between the first and second half of the 2010s.
Another study using this dataset looked at how long women reported trying to become pregnant, finding no significant change overall between 2002 and 2017. The time to pregnancy slightly increased over time for women who had prior children and women over 30.
The fact that both measures of infertility used in these papers “show no or little change in medically-defined infertility offers strong evidence against the idea of an infertility ‘explosion,’” Tierney said, despite increases in the rate at which people seek treatment for infertility and a small increase in people’s perceptions that they are infertile.
None of this is to dismiss the importance of better understanding infertility and reproductive health, Gemmill said.
“I fully think that we need more research on environmental contaminants and sperm and reproductive health conditions,” she said. “But I don’t think it’s at the level — at least based on the human studies that I’ve seen — where it’s going to impact birth rates at a population level. What is happening in the U.S. right now is because of social change.”
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