Over the last 55 years, young girls in the US have been getting their first periods earlier and earlier.

Nowadays, the average age is roughly 12. Some girls may menstruate as early as 8, according to Healthline.

New findings unveiled on Sunday at the Endocrine Society’s annual conference in San Francisco propose an unexpected factor that might affect the timing of this significant event: paw-paw.

“Young girls are beginning puberty sooner than in past generations, potentially increasing their chances of health issues down the line,” explained Xin Hu from Emory University’s Rollins School of Public Health in Atlanta in a statement.

“Our goal was to investigate the reasons behind this trend by examining the impact of environmental exposures passed down from grandparents on the age at which girls experience their first menstruation.”

Researchers tapped into the Child Health and Development Studies (CHDS), which began in the 1960s, measuring thousands of small molecules in blood samples taken from 249 couples.

Those chemical and metabolic profiles were then linked to puberty onset ages in their daughters (247 girls) and granddaughters (139 girls) — the latter born around 1990.

While the median age at first period remained stable between grandmothers and mothers, it dropped a full year between generations in the granddaughters.

The team found that specific chemicals — including phenoxyethanol, a preservative in personal-care products and foods — were associated with earlier puberty, especially when both parents had similar exposure levels.

Importantly, they found maternal and paternal exposures influenced timing, but it was the father’s contribution that stood out.

“While we found that both the mother’s and father’s exposures were linked to when their daughters and granddaughters began puberty, the father’s influence was surprisingly strong,” Hu said.

“Paternal exposure to environmental chemicals may play an unrecognized but critical role in shaping offspring endocrine health.”

The study is significant, as earlier puberty has been associated with an increased risk of Type 2 diabetes, obesity, certain cancers and depression.

“These findings highlight that prevention is possible if we identify mechanisms to protect future daughters and granddaughters, which cannot be effective if we do not consider the male line,” Hu said.

These results are also important in light of concerns that chemicals in our environment — from microplastics to forever chemicals — are leading to long-term health risks for us, as well as our descendants.