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. 

Previously, scientists have suggested possible causes including obesity, diet, socioeconomic status and potential exposure to substances such as phthalates that can disrupt sex hormones. 

Shaw, a co-senior author of the new study, acknowledged a link between early puberty and excess weight in young girls. “I do think it plays a role, but in my practice, it’s not just those who are overweight or obese who are having early puberty,” she said. 

While the timing of puberty may depend at least partly on genetics, a rapid change points “100% to environmental factors,” Shaw said. That’s what led the researchers to search for a compound that children might commonly be exposed to. 

If Shaw and her team have found a compound that might affect when the brain sends the signal to begin puberty, they will also have discovered the mechanism at the root of the change in timing, which population studies haven’t been able to do. 

Combing through 10,000 compounds in a library of licensed pharmaceuticals, environmental chemicals and dietary supplements, the researchers found several that might influence the timing of puberty. But children were most likely to be exposed to only one of them: musk ambrette, according to the report, published in Endocrinology. 

Musk ambrette, a synthetic form of the fragrance, could latch onto a puberty-related receptor in the hypothalamus, which would lead to the release of GnRH, a hormone involved in the maturation of sexual organs and the production of estrogen, testosterone and progesterone.

Musk ambrette is widely used in inexpensive or counterfeit fragrances and other scented personal care products, Shaw said. But it has also turned up in surveys of wastewater and in the bodies of freshwater fish, the researchers noted.

The next step for the researchers was to test the impact of musk ambrette on human hypothalamic cells and on zebra fish larvae. 

They found that in both the fish larvae and the human cells, the compound sparked the production of GnRH.

The new study is just a first step, Shaw said. Future studies will look at the impact of musk ambrette on mammals, such as rodents, and blood levels of the compound in humans, she added.

Shaw suggests that until more is known, parents hoping to prevent early puberty should check ingredient lists for musk ambrette on any cosmetics, fragrances and household products their children might use. 

The new study is looking at a very important topic, said Dr. Apisadaporn Thambundit, a pediatric endocrinologist who is an assistant clinical professor of pediatrics at UCLA. 

However, “I don’t think it’s strong enough to suggest anything that parents can do,” she said. She was surprised that phthalates, which have been linked to early puberty, didn’t come up in the research. 

Jasmine McDonald, an associate professor in the department of epidemiology at the Columbia University Mailman School of Public Health in New York City, said the new findings “as a first step are great.” 

A major strength of the study is that it didn’t start with a candidate compound, McDonald said. Instead, the researchers had a biological mechanism in mind and then looked for compounds that might play a role.

Based only on this study, it’s too early to consider banning or restricting a compound, McDonald said. But families might cut back on products with strong scents.

“If you need a lotion, it can be scent-free,” McDonald said. “In the shower, you can avoid scented body washes and shampoos.”