The beginning of adolescence is a tough time for any girl. It’s harder when you’re growing up in a tough neighborhood and go to a rough school. And it’s really hard when you face all the surging hormones and other tribulations of puberty before you even reach your eighth birthday.

If this sounds unnatural, it’s the reality for many young girls of color who experience early signs of puberty at alarming rates. The latest research adds to a growing body of evidence suggesting that an array of social and environmental factors may be causing girls’ bodies to develop prematurely. The New York Times reports that the potential causes flagged by researchers include exposures to chemical contaminants and obesity. The study-supported by the Breast Cancer and the Environment Research Centers-looked at 1,239 girls screened in Manhattan, Cincinnati and San Francisco. It reveals stark racial disparities.

The girls who developed breasts early, as young as age seven, were disproportionately Black and Latina. Black 8-year-olds were more than twice as likely as white girls to develop breasts. As the NYT reports:

 At 7 years, 10.4 percent of white, 23.4 percent of black and 14.9 percent of Hispanic girls had enough breast development to be considered at the onset of puberty.

 At age 8, the figures were 18.3 percent in whites, 42.9 percent in blacks and 30.9 percent in Hispanics. The percentages for blacks and whites were even higher than those found by a 1997 study that was one of the first to suggest that puberty was occurring earlier in girls.