Researchers from the National Institute of Environmental Health Sciences identified a compound that affects an area of the brain that triggers hormone production.

The age when girls hit puberty has been falling at an alarming rate for decades, and scientists have struggled to explain why. New research suggests a compound found in a wide variety of products — from cosmetics to air fresheners to detergents and soaps — may send a signal to an area of the brain that triggers the start of puberty.

It’s the first time researchers have looked at the possible impact of environmental chemicals on the brain to explain the rise in early puberty, said Dr. Natalie Shaw, a pediatric endocrinologist at the National Institute of Environmental Health Sciences in Durham, North Carolina.

Starting puberty significantly early — younger than age 8 in girls, 9 in boys — may have health effects lasting into adulthood, including higher risks of breast cancer, diabetes and heart disease. It can also lead to shortened stature in both girls and boys. In May, a study from the Harvard T.H. Chan School of Public Health found that 15.5% of girls experienced early periods — younger than age 11 — and that 1.4% started menstruating younger than age 9.