Is there any truth to reports that girls are hitting puberty earlier these days?

There is no straightforward answer to this question. The whole issue of the timing of puberty, especially among girls, is an area of active discussion and research. Despite discussion to the contrary, it is not completely clear that puberty is now occurring at an average earlier age; while several large surveys have suggested that breast development in girls is happening earlier, there have been problems with how the studies were done. In addition, it is clear that the timing of the first menstrual period has not changed over the past 50 years or so.

The timing of puberty is influenced by many factors, most importantly genetics (ethnic group, timing of parents' puberty, etc.). Of the environmental factors that affect puberty, nutritional state is the most important. Other possible environmental factors include endocrine-disrupting chemicals (such as pesticides), stress, climate and light. It has long been known that heavier children tend to go into puberty at a younger age than do thinner ones. So, given the explosive rise in obesity among children in the U.S., obesity may well be contributing to an earlier onset of puberty.