The Average Penis Length Is Increasing, Which Could Make Things…Harder

Key Points

• Penis length can be a point of pride for men; hence, the phrase "dick-swinging contest."
• A recent study shows that the average penis length is increasing relatively quickly, which could seem like good news to guys around the world.
• It is, in fact, not great news, as the rapid rate at which penile length is increasing could have repercussions on male reproductive health and potentially human reproduction as a whole—although more research is needed.

Male reproductive health has taken a downturn relatively recently. That trend in male sexual health prompted researchers to determine if other changes were occurring. The results—they concerned, in part, average penis length—were surprising.

What is the study about men's penis length?

Studies have revealed a worrying trend in male reproductive health, from declining sperm counts to lower testosterone levels and increasing genital defects in male babies. These trends prompted Michael Eisenberg, M.D., a professor of urology at Stanford University School of Medicine in Palo Alto, California, to wonder if there may be other concerning changes.

Eisenberg led a team that sought to discover whether there was any variation in penis length. He assumed they would find a declining trend.

"Given the trends we'd seen in other measures of men's reproductive health, we thought that there could be a decline in penile length," Eisenberg said in an interview with Scope, a Stanford University blog, in February 2023. "We conducted a meta-analysis in which we examined all reports of penile length, and what we found was quite different from trends in other areas of male fertility and health."

The average erect penis length has increased by 24 percent over the past 29 years, from 4.8 inches to 6 inches, according to the meta-analysis. The findings contradict previous research by scientist Shanna Swan that suggested chemical exposures are shrinking penises.

Such rapid growth could be worrying, Eisenberg said.

"Any overall change in development is concerning because our reproductive system is one of the most important pieces of human biology," Eisenberg said. "The increase happened over a relatively short period. If we're seeing this fast of a change, it means that something powerful is happening to our bodies."

How did the study work?

How has penile length changed over time and in different geographic regions? That was the subject of the 2023 study published in the World Journal of Men's Health. The researchers evaluated and aggregated a series of studies published between 1942 and 2021 that measured men's erect penile length.

The pooled data included measurements for flaccid length and stretched length, the latter being an estimation of erect length. The measures were done in a lab using penile injection and spontaneous erections. There were no self-reported measurements due to the possibility of inherent biases.

The data was gathered from 55,761 adult men ages 18 to 86 across the world. After adjusting for subject age, subject population and geographic region, the researchers found that erect penis length had increased significantly from 4.8 inches in 1992 to 6 inches in 2021.

The increases varied across different geographical regions. European and Asian men experienced the greatest increase in phallic length, while North American men's penile length slightly decreased.

What are the potential causes of an increase in penis size?

Surprised by the findings, Fenwa Milhouse, M.D., a board-certified urologist and the co-founder of Down There Urology in Chicago, who was not involved in the study, felt there could be something negative lurking behind the trend.

"People are probably going to say, 'This is a good sign; we're trending in the right direction,'" she said. "However, whenever you see such a drastic increase happening in such a short span, it could be a sign that there's something concerning happening that requires more research into."

These findings could be attributed to a variety of factors. Endocrine-disrupting chemicals in our environment, such as pesticides and hygiene products, could interfere with our hormonal systems, Eisenberg said.

These environmental exposures have been linked to earlier onset of puberty in boys, which can affect genital development, a 2019 study suggested.

"The penis grows during puberty, it doesn't grow during male adulthood, but these were adult males that were measured," Milhouse said. "Theoretically speaking, if puberty is happening earlier or occurring over more years, then the penis may also be exposed to more growth. Also, chemical exposures from the foods we eat and those in our environment could be changing our biological processes."

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Another plausible reason for the change could be tied to increasingly sedentary lifestyles and unhealthy eating habits that could lead to reproductive changes.

Researchers don't yet know the possible health implications. Penile length, in isolation, is not a primary determinant of male fertility. More comprehensive research is needed to identify the causes of this trend, including how shifts in lifestyle, diet and exposure to environmental factors play a role in these recent trends.

"However, if these changes are indicative of broader shifts in male reproductive health, such as hormonal changes or sperm quality, it could potentially have implications on male fertility," said Justin Houman, M.D., a reproductive urologist and men's health specialist at Tower Urology in Los Angeles and the chief medical officer for MANUAL, a mental and physical health resource for men, who was not involved in the study.

"That's why we need more research on whether this trend is associated with broader trends in male reproductive health," Houman added.

What are the limitations of the penis length study?

While the measurement techniques were the same across all studies, there could have been changes in external factors, such as temperature and the state of arousal, that might cause slight variations in penile length.

The researchers also considered that volunteer bias may have occurred in some of the studies.

Where does the research go from here?

The next step, Eisenberg said, should be to look at other demographics, such as the pediatric population, to see if there are any other similar changes. Systematically measuring penile length, just as we measure height and weight annually across the United States, can be an early indicator of changes in human development.

"If there's granular data on lifestyle factors or environmental exposures, we could try to understand why this may be happening," Eisenberg said. "It's important to look into whether there are any changes occurring to women's reproductive organs."

Hormone assessments and fertility evaluations could help to provide a clearer picture of these trends, Houman said. In addition, future collaboration between urologists, endocrinologists and reproductive specialists could unravel the potential implications on male health.

"Another thing we have to consider is, with all these trends in declining sperm counts and testosterone levels, are we really potentially having a decline in fertility, or are we just discovering this now?" Milhouse said.

Technology has changed how we approach difficulty conceiving.

"Thirty years ago, an infertile couple may not have seen a fertility specialist, but people now know that there are things that can be done as compared to 30 or 40 years ago," Milhouse said. "It could be that we're discovering more cases now because we have more access to fertility specialists, that's another important factor to consider moving forward."