Researchers at Stanford University have some good news and some bad news, all in the same package. In a new study that was published rather ironically on Valentine’s Day, they learned that over the last 30 years, the average erect penis length has increased by nearly 25% globally. The problem? This phallic enhancement is correlated with a steep decline in sperm counts and testosterone levels, which has many experts worried that a reproductive health crisis may be looming.

It’s getting cramped down there

A study led by Professor Hagai Levine of the Hebrew University of Jerusalem found that, over the past five decades alone, men’s sperm count worldwide has halved. From 1963 to 2018, the results show that sperm counts dropped by 1.2% per year on average. But from 2000 to 2018, the rate of decline was a staggering 2.6% per year, showing that this is an accelerated issue that shows no sign of stopping.

Even though one sperm is needed for fertilization, there’s a reason why the testicles produce so much sperm: most simply can’t survive the journey to the uterus. For optimal fertility, a healthy concentration of sperm is required of the order of about 40 million sperm per mL.

If this minimum threshold is not crossed, conception is difficult. If follows that as the sperm crisis unfolds, an increasing number of men will likely have to access assisted reproduction. The researchers in Israel report a drop in mean sperm count from 104 to 49 million per milliliter of semen, which is dangerously close to a tipping point in global fertility.

In tandem, testosterone levels are also dropping. A 2007 study found that the average American man’s testosterone levels have declined by about 1% per year since the 1980s. This means, for example, that a 60-year-old man in 2004 had testosterone levels 17% lower than those of a 60-year-old in 1987.

Doctors have been studying these trends with concern for some time. Among them is Michael Eisenberg, a professor of urology at Stanford Medicine, who wondered whether the forces that have caused this drop in sperm counts and testosterone levels may have also altered men’s physical anatomy.

Given these trends, as well as other measures of men’s reproductive health, Eisenberg had a hunch that men’s penises were getting shorter. To get to the bottom of things, he and colleagues embarked on what could be called the world’s most scholarly dick measuring contest.

The researchers didn’t get their hands dirty though, but rather systematically scoured the scientific literature and analyzed the findings of 75 reputable studies, which were conducted between 1942 and 2021 and involved over 55,000 men. When they crunched the numbers, everyone was surprised that penis length had actually increased rather than decreased over time.

“We looked at flaccid, stretched and erect length and created one large database of measurements. What we found was quite different from trends in other areas of male fertility and health. Erect penile length is getting longer, from an average of 4.8 inches to 6 inches, over the past 29 years,” Eisenberg said in an interview with Stanford’s Scope.

Bigger penis, bigger problems

Such a huge jump in penis size over such a short time is obviously unnatural and could be a physical symptom of a host of problems that may plague men’s reproductive health.

It’s not clear at all what is causing this great lengthening, but scientists have a hunch that exposure to pesticides and chemicals in personal hygiene products that may be disrupting the body’s natural hormones could be to blame. The same forces may also be responsible for the decline in sperm counts and testosterone.

“These endocrine-disrupting chemicals — there are many — exist in our environment and our diet. As we change our body’s constitution that also affects our hormonal milieu. Chemical exposure has also been posited as a cause for boys and girls going into puberty earlier, which can affect genital development,” Eisenberg said.

For now, the researchers advise caution as they try to look at other patient populations to see if they — and other research groups — can replicate the findings elsewhere. There’s also the matter of women’s reproductive organs. If penises are so obviously altered by the environment, what happens to vaginas? That’s also a serious line of inquiry that the researchers are pursuing.

“Just as we measure height and weight every year across the U.S., this is something else we could measure in a systematic fashion, because it may turn out to be an early indicator of changes in human development. Also, if there’s granular data on lifestyle factors or environmental exposures, we could try to understand why this may be happening. Lastly, I think it’s important to ask if there are similar changes occurring to women’s reproductive organs,” the researchers said.

The new findings appeared on Feb. 14 in The World Journal of Men’s Health.