More and More Girls Hitting Puberty by Age 7 And the percentages nearly double by age 8 By Kate Seamons, Newser Staff Posted Aug 9, 2010 6:51 AM CDT Updated Aug 14, 2010 6:16 AM CDT 41 comments Comments At age 8, 18.3% of white girls, 42.9% of black girls and 30.9% of Hispanic girls have hit puberty, says the study. (Getty Images) (Newser) – Today's girls are even more likely to enter puberty by age 7 or 8, finds a new study. At age 7, 10.4% of white, 23.4% of black and 14.9% of Hispanic girls had hit puberty, based on their breast development. Those numbers nearly double just a year later, to 18.3% in whites, 42.9% in blacks, and 30.9% in Hispanics. The percentages were even higher than those noted in a landmark 1997 study that was among the first to suggest that puberty was occurring earlier than commonly thought in white and black girls. Because some dismissed the 1997 study on the grounds that doctors may have classified fat deposits as breast tissue in some girls, for the new study, researchers thoroughly trained the examiners who reviewed the 1,239 girls ages 6 through 8. Though the study found that overweight girls were more likely to sprout breasts earlier, the lead researcher thinks chemicals may play a role, too. “We need to think about the stuff we’re exposing our bodies to and the bodies of our kids," he said, adding that he is doing follow-up testing on the girls' hormone levels and chemical exposure. The New York Times notes that while breast development may be occurring earlier, the average age of first menstruation remains relatively unchanged, at between 12 and 13.