More girls are starting their periods earlier than ever before — and experts may finally know why. Researchers say the average age for menstruation has dropped from 12.5 to around 11.9 years. That may not sound dramatic, but it’s a big shift for young girls still in primary school.

“It was scary and confusing,” says Milly Watmore, who got her first period at just ten. “I didn’t know what to do, and I was so embarrassed at school.” She’s not alone — the number of girls starting before age 11 has nearly doubled in recent decades, according to a Harvard University study.

Doctors believe several factors play a role. Rising childhood obesity, stress, and exposure to hormone-disrupting chemicals in plastics and cosmetics all contribute. “Fat tissue increases estrogen, which can trigger early puberty,” explains gynecologist Dr. Tania Adib. Genetics and diet may also influence when a girl starts her period.

Experts warn this trend can cause both emotional and physical harm. Early puberty is linked to depression, anxiety, and even higher risks of heart disease and cancer later in life. “Parents need to talk openly and early,” says Dr. Shazia Malik. “Understanding what’s happening helps girls feel less afraid — and more in control.”

Starting puberty too soon can be frightening for a child — but awareness, care, and conversation can make all the difference.