Fast Facts about Precocious Puberty

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  • The mean age for a girl's first period is 12.75 years.

  • Precocious puberty is defined as the onset of true puberty before 8 years of age in girls or 9 years of age in boys. (Boepple, et al. Endocrinology, Surgery, and Technology, Vol 1, 1996)

  • Isolated breast development that doesn't progress to the rest of puberty is called premature thelarche, and is a different, benign condition.

  • Precocious puberty is 10 times more common in girls than in boys. Sexual development may begin at any age. Pregnancy has been reported as early as 5 1/2 years old.

  • The Lawson Wilkins Pediatric Endocrine Society recommends evaluating for an underlying medical condition in Caucasian-American girls who have development of breast and/or pubic hair before age seven and in African-American girls before age six (Kaplowitz and Oberfield, Pediatrics 1999 Oct;104(4 Pt 1):936-41). These medical conditions include tumors, cysts, thyroid problems, McCune-Albright syndrome, or external sources of estrogen. Doing studies to look into these possible causes is especially important in girls younger than 6, and in all boys.

  • The earlier before age 12 a girl starts her period, the higher her lifetime risk for breast cancer (probably from the prolonged estrogen exposure). The highest average risk for breast cancer is in non-Hispanic white women, where it is 1 in 8, or 12.5%. In all girls who start their periods before the age of 12, taken together, the risk is 16.25%.

  • As a girl reaches maturity, she needs to be made aware of controllable risk factors for breast cancer, such as use of estrogen-containing birth control pills (10 years of use would raise her risk to about 22%), first pregnancy after age 30 (if she did this also, it would raise the risk to about 35%), high-fat diet, alcohol use, fertility drugs, pesticides, and radiation exposure. Each of these factors multiplies her accumulated risk.
Author and Review Info
Created By: 
Alan Greene MD FAAP
Reviewed By: 
Khanh-Van Le-Bucklin MD & Liat Simkhay Snyder M.D.
Last Reviewed: 
February 6, 2008