Penises Have Grown Dramatically Over Past Few Decades, Study Finds

It’s well-documented that since the mid- to late-twentieth century, children have begun entering puberty earlier than their predecessors. During the early 1900s, girls typically began menstruating around age 16. Today it’s not unusual for girls to enter puberty by age 10 and begin menstruating by age 12. But a new study has found that there’s also been one significant change for people with penises: Their members have grown dramatically in length over the past 30 years.

Earlier onset puberty has also become increasingly common in boys, with many beginning puberty by age 10, about a year sooner than they used to. Other reproductive changes have also become prominent in recent decades, including changes in sperm count and quality, but no clear cause has been determined. Based on the presence of these changes, Stanford Medicine urology professor Michael Eisenberg, M.D., decided to investigate changes in penile anatomy. His findings were published in the World Journal of Men’s Health.

With his team, Eisenberg analyzed data from more than 55,000 men gathered from 1942 to 2021. They discovered that the average erect penile length had increased by 24% over the last 29 years.

“We looked at flaccid, stretched, and erect length [of penises] and created one large database of measurements,” explained Eisenberg. “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.”

Reasons for the change are unknown, but what’s troubling to Eisenberg and his team is the rapidity with which such dramatic change took place.

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

Researchers speculate that reproductive changes may be caused by the population’s increased BMI, sedentary lifestyle, or exposure to endocrine-disrupting chemicals commonly found in plastics, food, makeup, and other modern everyday items. Those endocrine-disrupting chemicals are practically ubiquitous and interfere with the body’s normal use of hormones, per previous Fatherly reporting. They can cause lower sperm count in people with penises and even cause early menopause in people who menstruate.

Another theory suggests that earlier onset puberty, which is becoming more common, provides a longer window of time for penis growth since the penis continues to grow until puberty ends, generally around 18 years of age. However, the age at which puberty may ends may shift as the age it starts becomes earlier.

“There could be a number of factors at play, such as chemical exposure, like pesticides or hygiene products, interacting with our hormonal systems. These endocrine-disrupting chemicals -- there are many -- exist in our environment and our diet,” Eisenberg said. “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.”

There are limitations to the data obtained for the study — different measurement techniques may have been used, and a portion of erect length data was self-reported. Measured lengths could also have been affected by temperature, body size, level of arousal, and other environmental factors.

More research is needed to determine if the results are repeatable and if similar physiologic changes are occurring in people with vulvas.