When Frank Biro walks into to a class of second- or third-graders these days, there are almost always a couple of girls who look different than the rest.

“There will be quite a few girls that look like they’re going into early puberty,” says Dr. Biro, a professor of pediatrics at Cincinnati Children’s Hospital Medical Center who gives talks about puberty at schools occasionally.

Dr. Biro researches a phenomenon that has increasingly captured the attention of researchers: Puberty appears to be starting earlier in healthy girls, and possibly even boys. At Kaiser Permanente in Northern California, clinicians begin assessing girls for changes related to puberty at age 6.

“In general, we think that 7 is now probably a normal age to have some signs of puberty,” says Louise Greenspan, a pediatric endocrinologist at Kaiser Permanente who also researches puberty. “So the cutoff for precocious puberty is a gray zone now.”

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Precocious puberty is a medical term for puberty that begins in girls under 8 and boys under 9, sometimes from an underlying condition, such as a brain tumor. Often the cause remains unknown. Treatment is often used to halt or slow it down.

The health consequences of earlier onset of puberty are myriad. A study published in the journal Pediatrics in May found that girls who started puberty earlier had a higher risk of depression in early adolescence.

“We know that the early-maturing girls are at an increased risk of some of these risk-taking behaviors: alcohol use, smoking, drug use and earlier engagement in sexual behaviors,” Dr. Biro says. “We also know some of the longer-term consequences. As adults they’re at higher risk for having obesity, Type 2 diabetes and breast cancer.”

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