Puberty Starts Earlier Than It Used To. No One Knows Why.

Marcia Herman-Giddens first realized something was changing in young girls in the late 1980s, while she was serving as the director for the child abuse team at Duke University Medical Center in Durham, N.C. During evaluations of girls who had been abused, Dr. Herman-Giddens noticed that many of them had started developing breasts at ages as young as 6 or 7.

“That did not seem right,” said Dr. Herman-Giddens, who is now an adjunct professor at the University of North Carolina Gillings School of Global Public Health. She wondered whether girls with early breast development were more likely to be sexually abused, but she could not find any data keeping track of puberty onset in girls in the United States. So she decided to collect it herself.

A decade later, she published a study of more than 17,000 girls who underwent physical examinations at pediatricians’ offices across the country. The numbers revealed that, on average, girls in the mid-1990s had started to develop breasts — typically the first sign of puberty — around age 10, more than a year earlier than previously recorded. The decline was even more striking in Black girls, who had begun developing breasts, on average, at age 9.

The medical community was shocked by the findings, and many were doubtful about a dramatic new trend spotted by an unknown physician assistant, Dr. Herman-Giddens recalled. “They were blindsided,” she said.