Dr. Liz Lyster: Moms approach me on a regular basis to ask: Is it true that girls are starting to develop breasts and menstruate earlier than previous generations?

Yes, it is true. The trend towards earlier puberty in girls started over a century ago. Back then, the change was due to good developments: better nutrition, better sanitation, and better prevention and treatment of infectious diseases.

Nowadays, however, the causes spurring a further drop in the age of onset of puberty are not beneficial. They include too much unhealthy food, too little exercise, and unknown environmental factors. At this point, doctors are even debating whether or not to decrease the lower age limit of the "normal" onset of puberty, from age 8 to age 7 for white girls, and to 6 for African-American girls.

Earlier onset of menstruation (and later, menopause) has been linked with breast cancer later in life, although the reasons for this are not clear. One piece of good news in all of this is that earlier breast development does not necessarily mean earlier onset of a menstrual period in an individual girl.

That is, while puberty may begin earlier, there is a longer delay between the appearance of breast buds, the development of pubic hair (the adrenal glands getting started), and the onset of menstruation. The average age of onset of menstruation in girls is 12 years old -- slightly earlier for Latina (12.09) and African-American (12.06) than white girls (12.5).

While the search continues for scientific explanations for this trend, we have to remember that although they may look more developed on the outside, they are still our little girls, and we have to treat them in age-appropriate ways. Their mental and emotional maturing still requires the same "ages and stages" as it did for us.

"Doctor Liz" is a gynecologist whose mission is to help women balance hormones, lose weight, and regain health and balance in their lives. She did her undergraduate studies at Cornell University, medical school at UC Irvine, and earned her Master of Public Health degree at UCLA in Health Education. Doctor Liz is in private practice in Laguna Beach, California and is mom to two active boys, ages 8 and 10.