Girls are going through puberty increasingly early, with some growing breasts as young as age seven, according to a new book. Doctors Julianna Deardorff, a psychologist, and Louise Greenspan, a pediatric endocrinologist, have authored The New Puberty: How To Navigate Early Development in Today’s Girls, which looks at the phenomenon of girls who are going through early puberty and the environmental, biological and socioeconomic factors that influence the change.The doctors spoke to NPR’s “Fresh Air” this week about the results of a lengthy study they conducted which was funded by the National Cancer Institute and the National Institute of Environmental Health Sciences. The pair have followed 444 girls in the San Francisco Bay area since 2005, from age six to eight.In the past, eight was the normal age for starting puberty, Greenspan told “Fresh Air,” explaining that less than 5% of girls would start to develop breasts and pubic hair before that age. But Deardorff and Greenspan’s study found that at age seven, 15% of girls had breast development and at age eight, a startling 27% of girls had breast development.The doctors found race also may play a factor in when puberty starts: 25% of Black girls had breast development at age seven, compared to 15% of Hispanic girls and only 10% of white girls and 2% of Asian girls. There was a similar pattern in pubic hair development.Deardorff and Greenspan were careful to distinguish between puberty and sexuality, explaining that puberty does not necessarily mean the beginning of sexuality for girls if “the adults in [children’s] lives don’t put [puberty] into a sexual context.” However, Deardorff added that girls who develop early are affected, even burdened, by early development: “It has been established that girls who enter puberty earlier are more likely to have symptoms of anxiety, higher levels of depression, initiate sex earlier and sexual behaviors earlier.”The pair are investigating causes for this new pattern, which they call “puberty prompters,” which include from environmental exposure to BPA (the chemical compound in plastics) to soy, which seems to be protective against the onset of puberty. You can read more about their startling findings on their “Fresh Air” transcript here.