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Scientists are perplexed and concerned by a “worldwide” 24 percent increase in the average erect penis length from 4.8 inches to 6 inches, according to a new study published by a team of researchers from Stanford, Emory University, and several universities in Italy.The study examines 75 different research papers published between 1942 and 2021, which reported erect penis measurements in a total of 55,761 men. They made sure to only include studies where scientists were doing the measuring—versus patients self-reporting—and excluded studies where measurements were taken after pelvic surgery. The Stanford paper found, in particular, “an increase in the average erect penile length in men from 1992 to 2021” that held “across several geographic regions and subject populations.”
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Concerningly, the scientists do not know why erect penis sizes are getting longer, though they have a few theories. They theorize that there are global environmental causes, which may also be associated with boys (and girls) going through puberty far earlier than in previous generations. Notably, they also suggest that a “sedentary lifestyle” could be leading to hormonal changes that increase penis length. “It can be speculated that these changes may be linked with observations that pubertal milestones are occurring in younger boys than in the past,” they write. “Investigators have hypothesized sedentary lifestyle/obesity or increasing exposure to hormone-disrupting substances may play a role.”The researchers also note that there have been worldwide declines in sperm counts and testosterone levels and an increase in testicular tumors that also remain relatively mysterious, but could be caused by global environmental changes.Stanford Medicine interviewed Michael Eisenberg, one of the authors of the study, who said that this increase in penis length was not what the team was expecting: “Given the trends we'd seen in other measures of men's reproductive health, we thought there could be a decline in penile length due to the same environmental exposures,” he said. “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. If we're seeing this fast of a change, it means that something powerful is happening to our bodies. We should try to confirm these findings and if confirmed, we must determine the cause of these changes.”Eisenberg speculated that “chemical exposure, like pesticides or hygiene products” could be changing hormonal levels in men.There are a few things to keep in mind about the study. While it is a rigorous meta-analysis, there are billions of men in the world and it only looked at 55,000 of them. The researchers also note that penis measurements can be affected by temperature and body size, and other factors. Volunteer bias might also exist, but the researchers write that this should not have remained consistent enough over time to lead to the observed results.
"Given the important implications of genital development for urinary and reproductive function, future studies should attempt to confirm the trend and identify the etiology," they wrote.