Puberty is the process of physical changes through which a child’s body matures into an adult body. The stage of puberty in which a girl has her period is called menarche. Historical records show that in the late 1800s, the average age of menarche was around 15. The age at which puberty begins varies between individuals, but nowadays usually puberty begins between ages 10-11 for girls and 11-12 for boys. Girls usually complete puberty by ages 15-17 , while boys usually complete puberty by ages 16-17. There are a number of reasons why children in the U.S. may be developing at younger ages than they did in the past. There is no single reason but more a combination of factors that may be causing this including nutrition, obesity, and exposure to environmental chemicals.

Nutrition is one of the strongest factors affecting the onset of puberty. In the 21st century, children in the U.S. have improved nutrition resulting in rapid body growth, and increased weight and fat deposition. Surplus calories result in an increase in the amount of body fat, and in girls this signals to the brain the body has the resources available for the initiation of puberty and fertility.

Hormones are chemicals that are released within the body that an important role in the onset of puberty. They act as signals to trigger growth and development within the body. Research has shown that there are many chemicals present within our food, clothing, toys, water bottles, cosmetics, etc. that may mimic the hormones in the body and alter the timing of puberty. In girls, estrogen is the important hormone that initiates the development of the reproductive system. Parabens are chemicals with estrogen-like properties and are widely used in household products such as deodorants, shampoos, toothpaste, lotions, and make-up. Repeated exposure to hormone-disrupting chemicals such as phthalates, a chemical found in plastics, may influence the age at which puberty begins.