“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.”

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.”