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Research Summaries

All Research Summaries

Secondary Sexual Characteristics in Boys

Original article authored by: Marcia E. Herman-Giddens; Lily Wang; and Gary Koch

This summary includes the following sections:

Study Purpose

To fill a gap on descriptive data about stages of puberty among boys of different races and ethnicities, the authors used a population-based sample of 2,114 boys between the ages of eight and 19 to try to learn more about when boys reach different stages of sexual maturity.


The researchers followed sampling designs and protocols used in the CDC's National Health and Nutrition Examination Survey III (NHANES III). A team of trained interviewers — many of whom were bilingual — and physicians examined 2,495 boys for five stages of sexual maturity defined by Marshall and Tanner1 (a standard staging of sexual maturity developed in 1970). The "Tanner stages" used in this study (as well as previous studies) describe increments of genital and pubic hair development. Although the Tanner stages also address voice changes, facial hair growth, or other indicators, this particular study was limited to genital and pubic hair development.

After data on 381 boys were excluded because of various missing values (either demographic information and/or Tanner stages), the final sample included 2,114 boys. The sample represented 16,575,753 boys in the general population, with over-sampling of non-Hispanic, African-American and Mexican-American boys to allow analyses for these populations. The fact that this study used a population-based sample and explored sexual maturity for different races and ethnicities makes it unique.

The researchers acknowledged a number of potential data quality issues. Chief among these is the subjective nature of rating male genital development on a scale — even one that has been in use for many years and in which clinicians are well trained. The researchers also note that they did not collect data on boys younger than eight years of age, but the fact that so many 8- and 9-year-old boys in their sample already had begun genital growth suggests that data on younger boys should be collected in the future.



The researchers found that there are significant differences among White, African-American, and Mexican-American boys in terms of how soon they begin puberty, but they have no explanation for why this is so.

According to these data (and confirming some of the few other studies that examined racial differences in puberty), African-American boys showed pubic hair growth earlier than White boys (nine months earlier) and earlier than Mexican-American boys (one year earlier). Pubic hair growth equalized at the end of the development process, with all three groups completing pubic hair growth phases within five months of each other. However, African-American boys started and completed genital development a year earlier than either of the other two groups studied.

The ages at which boys end development do not seem to have changed much from prior studies. The researchers believe that this indicates earlier onset of puberty, with a longer developmental period.

In addition to their findings about earlier onset of puberty, the researchers found that all three groups of boys — White, African-American, and Mexican-American — were taller and heavier than boys in previous NHANES surveys.


Implications and Next Steps

Further research, the authors note, is warranted to understand these differences and explore possible explanations, such as the roles of diet and endocrine disrupters in the environment. Other possible implications include revising sex education programs and seeking answers to the question of whether the earlier onset of puberty may have long-term effects on boys' health as they mature.

Unfortunately, the researchers point out, the current NHANES survey does not collect data on puberty. If it does so again in the future, they hope it will address this issue for younger boys as well, to gain more information on the earlier onset of puberty identified in this study.

1Marshall, W.A. & Tanner, J.M. (1970). Variations in the pattern of pubertal changes in boys. Archives of Disease in Childhood. 45, 13-23.

Herman-Giddens, M.E., Wang, L., & Koch, G. (September 2001). Secondary Sexual Characteristics in Boys. Archives of Pediatric Adolescent Medicine. Vol. 155, 1022-1028.