Growing Up Too Fast: Premature Sexual Development in Boys

Every parent knows that girls are developing earlier than they used to, but boys’ sexual development is not as obvious.  A study published in late 2012 shows that the same concerns should apply to boys as girls.[1] This study, led by Dr. Marcia Herman-Giddens of the University of North Carolina at Chapel Hill, is an update to her study from 11 year ago with new information and better measurements.[2]

The new research is based on more than 4,000 American boys getting health care at 144 pediatric clinics across the United States. It was the first study to physically examine boys to measure their sexual development, which required parents to agree to have their sons’ pubic hair and genitals examined by a doctor. Because boys do not have menstrual periods like girls do, there is no easy way for doctors to tell if boys have entered puberty.  The researchers used a five-stage system called “Tanner Staging” to categorize their stage of puberty, from Stage 1 (the prepubertal stage) to Stage 5 (sexually mature). This study focused mostly on Tanner Stage 2, which is when boys begin puberty. The major measure was the size of the testes, which the doctors measured using a device called an orchidometer. The doctors also visually determined how much pubic hair each boy had. Testicles between 1.6 and 6 milliliters are considered Stage 2, as well as the very beginning of pubic hair growth.

The study found that based on testicular development, white boys reach Stage 2 at 10 years old, African American boys at 9 years old, and Hispanic boys at 10 years old. Based on pubic hair, the researchers concluded that boys were considered Stage 2 at a slightly older age: 11 for white boys, 10 for African American boys, and 11 years old for Hispanic boys.

Since this is the first study to measure both testes and pubic hair to determine when boys start puberty, it is difficult to compare it to previous studies to see if puberty is starting earlier now than for previous generations. However, one American study -– led by Dr. Frank Biro at Children’s Hospital Medical Center in Cincinnati –- had measured testes in Cincinnati boys between 1984 and 1987.[3] On average, boys in that study reached puberty (Tanner Stage 2) at the age of 12 with no difference between white and African American boys (Hispanic boys were included with white boys in this study). This is approximately a 2 year difference between the Biro study and the 2012 study. This difference raises the concern that boys are beginning to reach puberty much earlier than before.

Dr. Herman-Giddens’ previous study, which analyzed data from 1988-1994, did not measure testes and its genital staging was not as accurate as the 2012 study. In that study, by the age of 8, 38% of the African American boys had started genital development, as had approximately 28% of white and Mexican American boys. By 9 years old, 58% of the African American boys and approximately one-third of the white and Mexican American boys had started genital development. Based on the results of the 3 studies, boys are entering puberty earlier now than they did in the 1980s and 1990s.

Most adults think that kids are growing up too fast and these studies show that there may be a biological basis, not just a cultural one. Researchers have found that in girls, early sexual maturation can be brought on by excess body weight, apparently because estrogen is associated with body fat. Studies are needed to see how weight affects puberty in boys.[4] Regardless of the reason, the general trend appears to be that boys, like girls, are entering puberty earlier than they ever did before.

As parents, teachers, youth workers, and other adults try to help preteens and young teens steer clear of risky sexual behavior, it is helpful for them to understand that many kids are starting to experience hormonal changes and sexual development in third and fourth grade. These are young children — they are still learning to make change for a dollar and to spell simple words in school. Although puberty may just be starting, these children may not be thinking or acting like little boys and girls.

Neither of Dr. Herman-Giddens’ studies examines the boys’ behavior or adjustment, although previous studies of girls have indicated that early puberty is linked to depression, drug and alcohol use, and early sexual activity. Young kids that look older may tend to hang out with older kids, and may feel a need to prove themselves by acting older. They will need guidance and support from parents and other adults who need to be aware that despite the physical changes, these are still young children whose judgment is probably not as mature as their appearance.

All articles are reviewed and approved by Dr. Diana Zuckerman and other senior staff.

1. Herman-Giddens ME, Steffes J, Harris D, et al. Secondary sexual characteristics in boys: data from the pediatric research in office settings network. Pediatrics. 2012;130(5): 1058–68.

2. Herman-Giddens ME, Wang L, and Koch G. Secondary sexual characteristics in boys. Archives of Pediatrics & Adolescent Medicine. 2001; 155:1022-28.

3. Biro FM, Lucky AW, Huster GA, Morrison JA. Pubertal staging in boys. J Pediatr. 1995; 127(1):100–102.

4. Benedet, J., da Silva Lopes, A., Adami, F., de Fragas Hinnig, P., & de Vasconcelos, F. d. A. G. (2014). Association of sexual maturation with excess body weight and height in children and adolescents. BMC Pediatrics, 14(1), 72. doi:10.1186/1471-2431-14-72