The hormone estrogen is largely responsible for the differences between boys and girls. Children have low levels of this hormone, but during puberty, the levels increase and bodies change rapidly. Girls usually begin to experience puberty between the ages of 8 and 12, while boys begin between the ages of 9 and 14, notes MayoClinic.com 35. And it is the hormone estrogen that plays a major role in the transformation that occurs during that time.

Definition

According to the Encyclopedia Britannica, estrogen is a hormone that consists of estradiol, estrone and estriol 2. The ovaries produce it in girls, and the testes produce it in boys. Estrogen not only influences the female reproductive system, but also the growth of bones and muscles, as well as the differences in the body shape and size of men and women.

Estrogen Levels in Boys

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**According to the article Plasma Estrogens in Childhood and Puberty Under Physiological and Pathological Conditions by Frank Bidlingmaier, M.D., and colleagues, a boy under the age of 8 has less than 15 picograms per ml of estrone and estrodial in his body 1. After the age of 8, however, the amount slowly increases and peaks during puberty. For boys, estrogen plays a role in bone density, testicle size and the development of the voice box.

Estrogen Levels in Girls

According to Bidlingmaier and colleagues, young girls have the same amount of estrogen as boys. The estrogen level in girls heightens at puberty as well. Estrogen plays a role in the female menstrual cycle; it determines when a girl will receive her first period. Estrogen communicates to the uterus when to begin sloughing off the dead skin cells that cause menstruation. If there is not enough estrogen in a young girl’s body, she will not be able to menstruate properly.

Estrogen Levels at Puberty

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According to research conducted by Karen Oerter Klein and colleagues, published in "The Journal of Clinical Investigation," prepubescent girls produce a higher level of estrogen than prepubescent boys 4. It has been noted that this higher level of estrogen leads to girls going through puberty earlier than boys. It encourages growth to begin sooner and puberty to occur earlier than in boys.

Disorders Related to Estrogen Levels

High levels of estrogen in both boys and girls can indicate congenital adrenal hyperplasia. This is a genetic condition that affects the adrenal glands and can prevent a child from growing and developing normally.