The Pre-teen Girl Mystery

Girls have been hitting puberty earlier and earlier since the 1950s, but new research shows the trend suddenly speeding up—and a chemical found in everyday items may be the culprit.

05.22.09 5:53 AM ET

The concept of accelerated aging usually resides in the realm of science fiction, wrinkles in time, and five-year-old beauty queens. But growing up at warp speed is actually happening. Kids have been hitting puberty earlier and earlier since at least the 1950s—and new research shows that in the past two decades, the pace of this trend has picked up dramatically.

According to a study conducted by researcher Dr. Lisa Aksglaede and other scientists in Copenhagen and published in this month’s Pediatrics, girls are now developing breasts a full year earlier than they did in the early ‘90s. The researchers compared studies of the physical development of two groups of girls, the first group in 1991/1993 and the second group in 2006/2008. In the 1991/1993 studies, girls started breast development just shy of 12 years old. By 2006/2008, girls had reached that same level of physical development just before age 11. The more recent group’s menstrual periods also started at a younger age—about three months earlier than those of the girls in the ‘90s. Earlier physical development isn’t new—in the U.S., the onset of breast development for young white females is happening a year earlier than in the age of June Cleaver—but scientists are alarmed that the pattern appears to be speeding up.

“We are talking about girls who have not learned to make change for a dollar. They have limited knowledge and judgment, but they look older, which makes them vulnerable to exploitation.”

Why is this happening? Is it the hormones in our milk? The extra calories we consume? The chemicals in our environment? All of the above?

For years, the problem was chiefly attributed to our increasingly sedentary and junk-food-oriented habits, and that’s likely still part of it. “The changes in lifestyle in the past 50 years are incredible. The lack of physical activity and all the new kinds of junk foods are having an effect,” says Dr. Marcia E. Herman-Giddens, the principal investigator of the 1997 landmark study that was the first body of research to establish that puberty was happening earlier.

But body mass index doesn’t explain the Copenhagen study, in which researchers found that puberty did not discriminate by pants size—heavier and lighter girls are both developing breasts earlier.

“The chubbiness factor is not the whole story,” says Dr. Sandra Steingraber, author of “The Falling Age of Puberty in U.S. Girls,” a 2007 report commissioned by The Breast Cancer Fund. (There’s a well-established link between the early onset of puberty and the risk for breast cancer.) That report, which synthesized the scientific literature about the early onset of puberty, flags environmental chemicals, especially those found in plastics (called plasticizers), as a major cause. “We know we can accelerate the puberty rate of rats with plasticizers and certain pesticides,” says Steingraber, who is also an expert on the environmental links to cancer and reproductive health.

And increasingly, one particular plasticizer is being zeroed in on as Public Enemy No. 1: bisphenol A, or BPA, a chemical found in food and beverage containers, including baby bottles and children’s sippy cups.

The National Research Center for Women & Families, a nonprofit that promotes the health and safety of families, is working on getting BPA out of such containers because it mimics estrogen, the growth hormone that flips puberty’s “on” switch. A report from the California Breast Cancer Research Program found that BPA developed as a synthetic estrogen, and the science is solid enough that a grassroots campaign to ban BPA is becoming a groundswell. Two weeks ago, Chicago became the first U.S. city to ban the use of BPA in baby bottles and sippy cups. Minnesota also passed legislation this month that will ban the chemical by the end of this year. Various other states and municipalities are considering similar measures. “The only question is how much this chemical contributes to puberty, not if,” says Diana Zuckerman, the president of the National Research Center for Women & Families. “It’s an extremely likely explanation.”

Which prompts the obvious question: Why, in this age of knowing all we do about organic choices and the dangers of added chemicals, do we still have toxins like this in our baby bottles?

One reason is that the laws regarding toxic substances are governed by the Toxic Substances Control Act of 1976, which many experts say is in desperate need of an overhaul to require more regulation and testing of chemicals. To that point, Steingraber says she thinks the European’s Union’s "green" chemistry initiatives would be a good blueprint for the U.S. to follow. “We should be detoxifying our environment as a health precaution,” she says.

While parents should do their best to manage the external factors that may trigger early puberty, the reality is that, at least for now, society is going to have adjust to an accelerated puberty timeline. This is where it’s important to remember that puberty is much more than a set of physical changes—it’s also a part of neurobiology. The brain is completely re-sculpted under sex hormones, and social scientists are struggling with how society should adapt to the ever-younger “mature” girl.

“We are talking about girls who have not learned to make change for a dollar. They have limited knowledge and judgment, but they look older, which makes them vulnerable to exploitation,” says Zuckerman.

Indeed, the early onset of puberty brings a whole new set of conversations and complexities to the tween years. As if having the puberty and facts-of-life talk wasn’t loaded enough, how do you explain to your 11-year-old daughter with a full B-cup that she shouldn’t let boys touch her?

Dr. Tina Payne Bryson, a parenting expert, says parents need to address both the mechanics and the societal meaning of these changes. “Parents should tell their daughters that when their bodies start to look more and more like a woman’s body, men might notice their breasts, curves, and hips, but that having an adult-looking body doesn’t mean having to do adult things.”

“We also need to talk to them about when you would and wouldn’t be sexual with someone,” she continues. “This means telling a 10, 11, or 12-year-old girl that it’s not OK for anyone to touch her body until she’s older and can understand more about love and sex.” In an effort to avoid that conversation, some parents, like Steingraber, the mother of a 10-year-old girl, are taking proactive measures. “I think the evidence about the link between chemicals and the early onset of puberty is compelling enough to keep my kitchen stocked primarily with foods that come from farms that do not use pesticides.”

Hannah Seligson is a journalist and the author of New Girl on the Job: Advice from the Trenches. Her second book, A Little Bit Married , will be published by De Capo this spring. Her website is