Scientific American asked me to write about the enormous gaps in menstruation research for the May 2019 issue. One of the biggest: Why are girls starting puberty earlier than ever before?

The average age of menarche, or a girl’s first period, in the U.S. is now 12, according to the most recent data from the Centers for Disease Control and Prevention, down from 14 a century ago and as much as six months earlier than 20 or 30 years ago. But puberty does not start with menstruation. The onset of breast development, or thelarche, tends to come first. “We’re now seeing thelarche occur 18 months to two years earlier than we did a few decades ago,” says Frank Biro, who studies problems related to pubertal maturation at Cincinnati Children’s Hospital Medical Center. His research, published in 2013 in the journal Pediatrics, put the average age of breast development at 8.8 years old for African-American girls, 9.3 for Hispanic girls, 9.7 for Caucasians and 9.7 for Asian-Americans. “The age of breast development has clearly dropped, while the age of menarche has drifted down. They are both concerning,” he says.

And concerning for so many reasons: We don’t know why it’s happening. We don’t have the first clue what to do about it. Little girls are dealing with bras, pads and often, sexual aggression, long before they’re emotionally ready to do so. And as a culture, we don’t know what to do with any of this, so we end up making it about our discomfort with girls’ changing bodies. They are not the problem. And they deserve better answers.

Read more here.