An observational study indicates that penile length is increasing worldwide. Researchers say such changes are worrying, as changes in length may lead to infertility.
Researchers examined 75 studies on men's penile length published between 1942 and 2021. The data from 55,761 men suggests that erect penile length increased by 24% over the past 29 years across the Americas, Europe, and Africa. However, there was no difference in the length of the flaccid and stretched penis.
According to the study published in the World Journal of Men's Health, the average length of a flaccid (soft) penis is 8.7 cm (3.42 in), while the average stretched penile length is 12.93 cm (5.09 in). On average, a penis in an erect position is 13.93 cm (7.84 in) long.
Researchers are uncertain what increases penile length but say these changes may be due to pubertal milestones occurring in younger boys than in the past. Previous studies linked earlier pubertal growth to increased body sizes, including longer penises.
Such changes in penile length may also be associated with a sedentary lifestyle and obesity or increasing exposure to hormone-disrupting substances that exist in the environment and our diet.
"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," said Michael Eisenberg, M.D., a professor of urology at Stanford Medicine.
Penile length linked to fertility?
Researchers have previously studied the link between penile length and fertility, and there is still no conclusive answer.
A study from 2021 examined stretched penile length of 161 infertile and 503 fertile men. The average penis length of infertile men was shorter 12.3 cm (4.84 in) compared to the 13.4 cm (5.27 in) in the other group, while total testosterone did not significantly differ. The researchers conclude that it remains unclear whether the reduced length results from genetic or congenital factors associated with infertility.
In 2011, researchers examined how fertility is affected by anogenital distance (AGD), measured from the anus to the underside of the scrotum. They found that men with shorter AGD than the average (5.2 cm, 2 in) were seven times more likely to be sub-fertile, meaning conception takes longer than average but still exists.
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