Endocrinologists say they're seeing more girls with precocious sexual development, and some medical studies suggest the baffling trend is real, that the beginning signs of puberty are showing up earlier in today's girls than their mothers. Until recently, doctors and parents didn't expect to see budding breasts until around age 10.
Nobody knows what's causing the shift.
Fat is the leading theory, because childhood obesity has doubled in the last 20 years and body fat certainly can spur hormones. Nor can anyone explain the racial differences, or whether puberty is shifting for boys, who just now are being studied. In rare cases, a cyst or tumor may cause extremely early puberty, so doctors always check. Super-early puberty also can steal some growth, leaving girls a little shorter than they otherwise would be. But as younger puberty becomes more the norm, the bigger worry is how girls still at the age of Saturday morning cartoons handle the physical changes, especially when their playmates remain flat-chested or they attract unwanted attention from older boys.