While most girls will get their first period around age 12, the range can run from age 8-16. Most of these girls are normal by biological standards, because puberty is a complex process of brain, body, and hormonal development. Still, there appears to be a trend toward precocious puberty in some boys and especially in girls. Precocious puberty is the clinical term for those who experience abnormally or unusually early puberty.

Defining Normal Puberty

Every child is unique. When a child begins puberty depends on a variety of factors, including family history, ethnicity, and nutritional status.

The onset of puberty is marked by the appearance of pubic hair and breast buds in girls. Next come breast growth and body shape changes in girls and testicular growth in boys. Menstruation and voice changes come later. On average, menstruation occurs about two years after puberty begins.

Until recently, normal puberty was thought to begin between ages 8 and 14 in girls and between 9 and 12 in boys. But, recent research has found that puberty occurs as early as age six in girls of certain ethnic backgrounds.

Rare Causes of Early Puberty

In rare cases, especially when pubic hair is seen in children as young as five, precocious puberty can be caused by tumors of the adrenal gland, ovaries, or brain. It is also seen in those with rare genetic disorders, like McCune-Albright Syndrome. While the appearance of pubic hair in such a young child warrants a visit to the pediatrician to rule out any serious causes, it may be just another variation on the norm.

Growth and Puberty

When puberty comes too early, it can affect growth. By late puberty, most children have reached 95% of their adult height. When puberty starts and ends too early, the sex hormones that help harden bones can end their growth too soon. Other problems may surface later in life. For example, the earlier a woman starts menstruating the more at risk she is for diseases like breast cancer.

If tumors or other serious causes of precocious puberty are ruled out and if a child's doctor believes the progress of puberty could harm her growth, hormone agonists can cancel the hormonal domino effect and delay puberty until a more optimal time.

The Mystery of Puberty

Scientists and clinicians would like to clarify what is normal for the onset of puberty, but the issue is clouded by the controversy of how puberty begins. The process is an intricate interplay of brain activity that leads to hormonal secretion. While experts can name some of the hormones involved in puberty, they do not know the triggers.

Does Obesity Affect Puberty?

Studies have looked at the effect of increased body mass index (BMI) on earlier onset of puberty. One study found that the BMI in pubertal 6-9 year old white girls was markedly higher than the BMI in prepubertal girls of the same age. A smaller difference was noted for African American girls.

The relationship between obesity and early puberty is not clear-cut, however. Multiple factors are likely involved in the development of precocious puberty. Studies are under way to look at these potential contributing factors.