Puberty is the developmental stage where a child starts to become sexually mature. It can occur between ages 8 and 11 for girls, and 9 to 12 for boys.
As a child nears maturity, the brain -- specifically the parts known as the hypothalamus and the pituitary gland -- releases chemicals called hormones. The hormones regulate the reproductive organs of both males and females. Girls produce estrogen and progesterone, while boys produce testosterone. Growth hormones also begin to work, causing the body to become larger, sometimes very quickly. The body also makes follicle stimulating hormones, leading to hair growth.
All these extra hormones give rise to dramatic changes in the body.
The first sign of puberty in girls is breast development. Then hair starts growing in the pubic area and armpits, followed by acne around age 13. Menstruation is typically the last stage to occur.
In boys, the larynx lengthens and the voice "breaks" and then deepens. Also, there is growth in the testicles and penis, followed by hair growth in the pubic region and armpits. Acne and facial hair are the last developments.
Both girls and boys may also experience strong emotions or mood changes.