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Getting your first period can be one of the most fraught experiences of adolescence. It can be exciting, scary, painful, messy, embarrassing, or all of the above. And though the adults in your life can help you prepare for and understand what’s happening, they can’t do much to predict or control it when it does.

Except that now, some parents are trying to take a more active role. “Delaying my daughter’s first period is a goal I have in motherhood,” wrote Nicky Skinner, a nurse and health coach, on Instagram last month. Skinner has been concerned for years about the effects of certain chemicals on girls’ puberty, she told me in an email. Now that she’s a mom to a 4- and 7-year-old, she’s working to eliminate those chemicals from their lives.

Her post, which got more than 70,000 likes, is one of a few offering tips on pushing back the onset of menstruation (also called menarche), often involving changes to diet, personal care products, and even screen time. The parents involved are responding to a nationwide trend: The average age of menarche in the US has shifted earlier, from 12.5 between 1950 and 1969 to 11.9 between 2000 and 2005, according to a 2024 study.

The percentage of kids who get their first period before age 9 is also on the rise, more than doubling between the 1950s and the 2000s. Researchers are concerned about these trends because getting a first period earlier is associated with an increased risk of some health conditions, including breast cancer.

Even Health and Human Services Secretary Robert F. Kennedy Jr. has weighed in on the matter, claiming in an April appearance on Fox News that “girls are hitting puberty six years early.” He appeared to link the issue to children’s diets, arguing that “the food our kids are eating today is not really food.”

But experts say the shift toward earlier periods likely stems from a variety of factors, including increased nutrition, higher body weight, stress, and environmental influences. Researchers are particularly concerned about the impact of chemicals called endocrine disruptors, which can mimic the activity of hormones in the body, said Shruthi Mahalingaiah, a professor of environmental, reproductive, and women’s health at Harvard University. These chemicals include phthalates, which can be present in shampoos, lotions, and other common products.

Some experts say........

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