Precocious puberty, also called early puberty, is a medical condition that doctors have long recognized. It is five or six times more common in girls than boys. But these days, even girls without this condition are entering puberty earlier than their mothers and grandmothers did, often developing breasts and pubic hair several years earlier than what was previously considered the norm. In years past, girls typically began puberty at age 10 or 11. Researchers don't completely understand what's causing younger and younger girls to show signs of puberty.
Some researchers think it's hereditary.
Others credit chemicals in the environment for the trend, says Kaplowitz. These pesticides can break down into compounds that may have estrogenic activity. In the lab, he says, the substances have been shown to interact with estrogen-receptor cells. Thin girls and athletic girls tend to be on the late side. In a study he's preparing to publish, preliminary data support that view.