After receiving a partial vasectomy in 1930s London, famous poet W.B. Yeats may have been the first in the history of the English language to claim he was experiencing a "second puberty" — but he certainly wasn't the last. 100 years later, the strange phrase has become a hashtag viewed 57 million times on TikTok.

The vast majority of TikTok users swapping tales of a "second puberty" — most of them women — have not undergone partial vasectomies, to be sure. While Yeats' proclaimed second puberty referred to an awakening of sexual desire, these women say their bodies are undergoing inexplicable changes in different, often far less satisfying ways.

User madds.maxjesty posted a video encapsulating what many others are saying: "When people say ‘you've gotten bigger since high school' like yeah women go through a second puberty".

Reports of this second puberty appear to largely revolve around weight gain, but some women also talk about noticing changes in their skin or hair. These videos are characterized by a sentiment not uncommon on TikTok — the women insist this is something "no one is talking about."

As a 26-year-old woman myself, I decided to do some research. I created an Instagram poll asking my female friends if they feel they have experienced a second puberty. I did not explain what this phrase was supposed to mean. Of those who responded, 46% said yes, 7% said no, and the rest said they didn't know what I was talking about.

So there's probably something there, right?

Not a real thing

Let's be clear: "Second puberty" is not a medically recognized condition. People only go through puberty once in their lives. There is some nuance to this: Trans people who undergo hormone therapy may experience something much closer to the "second puberty" cisgender women have been discussing on social media.

But for the cisgender women, "there is no medical reason why there would be uniform weight gain for a woman in her 20s," said Eve Feinberg, a gynecologist and professor of reproductive endocrinology and infertility at Northwestern University in the US.

If this weight gain is happening, she said, it is probably due to lifestyle changes. "Often the first time people are really living on their own is in their 20s. Likely eating out more, drinking more and 'enjoying life' more all while exercising less."

And contrary to what many women on social media claim, Feinberg said it's probably not due to female hormones.

"While people love to blame 'hormones' for weight gain, the hormones that are really to blame are those that are associated with diet, things like insulin, ghrelin and leptin, and not female reproductive hormones like estrogen and progesterone," she said.

Naveed Sattar, a professor of Metabolic Medicine at the Institute of Cardiovascular & Medical Sciences at the University of Glasgow, agreed.

"I don't think hormones have anything to do with this," he said.

Like Feinberg, Sattar said much of this can be chalked up to lifestyle changes. He explained that data shows women do seem to have a higher likelihood of becoming overweight or obese compared to their male counterparts, but that this probably has little to do with genetics or a "second puberty".

Weight gain in younger women "may link to life stresses more rapidly impacting women when they become adults due to their higher volume of work – domestic and occupational plus less opportunities for activity – compared to men at this age," he said. "If these speculations are right, we need more flexible working for women – more opportunities to be active and more sharing of domestic duties."

TikTok and women's health

Conversations about weight gain or other body changes in your 20s may have once been confined to one-on-one conversations with friends, articles in women's health magazines or the doctor's office. But the advent of the internet has opened the conversation to the entire world, allowing anyone to insert their opinion or experience, regardless of qualification.

In truth, it's very common for women to gain weight in their 20s, and there are a myriad of reasons why this may happen. Along with pregnancy, women in their mid-to-late 20s take part in many activities associated with weight gain: quitting smoking, frequent alcohol consumption, cohabitating with partners, attending university and switching birth control methods. And some women will continue developing into their early 20s. Breast size, for example, can change frequently over the course of a woman's life.

A paper published in 2022 offers some insight into the situation: In a study of over 13,000 participants, researchers set out to track how a person's weight changes over the course of a decade based on age, sex and race.

They found that those who had gained the most weight over the course of the past ten years were the youngest participants — women between the ages of 36 and 39. Both Black women and Mexican American women (the study was conducted in the US) were more likely than white women to gain weight, but all groups of women were more likely to gain weight than all groups of men.

Notably, the researchers opted against including people younger than 36 in their study.

"If 30-year-old individuals were included, then weight gain calculations beginning at 20 years of age would be needed," they wrote. "This would be problematic because some 20-year-old individuals are still growing and developing physically."

So, there you have it. Although second puberty may not be a real thing, body changes during adulthood certainly are.

Edited by: Fred Schwaller