Puberty
Puberty is started by hormones, which are chemicals that tell parts of the body to do things. For reasons which are not completely understood, girls and boys now start puberty when they are younger than it happened to boys and girls in the past. Some girls now start puberty at age 9 or 10 or even earlier. For boys puberty is also happening earlier. A 2012 study study found that, on average, African American (Black American) boys begin puberty at age 9 while white and Hispanic boys start at age 10, on average. People around the world start puberty at different ages. The reasons for girls and boys starting puberty earlier might be that they eat healthier food and drink more milk. Other reasons might be chemicals in food, chemicals in plastic containers, chemicals in the air and chemicals in the water. The reasons are not known for sure.