30 studies conducted around the world show results that girls are starting puberty a year earlier than their grandparents and parents. In the studies, some researchers looked at the age girls started to grow breast tissue and others studied the age girls begin their first menstrual period. Both study groups had similar findings, but the research group who studied menstrual periods concluded that puberty onset decreased decades earlier than the results published in the breast tissue studies. Keep in mind that the menstrual period studies relied on girls reporting when they believe their first menstrual period started, which those recollections can be inaccurate.
Although we know that girls are starting puberty earlier than anytime in history, the studies that produced these results did not research the causes. We do have two possible reasons and it's up to the scientific community to continue further investigation. The first reason is the global obesity epidemic. Some research studies show that girls who are overweight enter puberty earlier than girls who are lean, this can be linked to higher levels of the fat-regulating hormone leptin. The second reason girls are entering puberty early has to do with increasing amounts of endocrine-disrupting chemicals in the environment. Chemical such as, DDT (dichlorodiphenyl-trichloroethane) and DDE (dichlorodiphenyldichloroethylene) have been associated with puberty at an earlier age. You can find these chemicals in products like toothpaste, soap, and make up.
To further your quest to learn more click here.