HealthDay News — American boys are maturing sexually at younger ages, results of a cross-sectional study suggest.

Puberty onset, as measured by the presence of pubic hair and testicular enlargement, is occurring approximately 6 months to 2 years earlier compared with studies dating back to 1930s, Marcia Herman-Giddens, PA, DrPH, of the University of North Carolina at Chapel Hill, and colleagues estimate.

The findings were published online in Pediatrics, and were also presented at the American Academy of Pediatrics annual meeting this week in New Orleans.

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Some differences in onset were noted between racial/ethnic groups, with black boys reaching puberty earlier than whites and Hispanics, the researchers added. Although the study did not assess potential explanations for the findings, exposure to chemicals, diet, physical activity levels and other lifestyle factors may play a role.

Recent studies have shown that girls are reaching puberty approximately one year earlier than they were 40 years ago, but less is known about puberty onset in boys. So Herman-Giddens and colleagues analyzed data from the American Academy of Pediatrics’ Pediatric Research in Office Settings (PROS) network, the National Medical Association’s Pediatric Research Network and the Academic Pediatric Association’s Continuity Research Network.

The study involved 4,131 boys aged 6 to 16 who underwent Tanner staging and measurement of testicular volume conducted by 212 practitioners in 144 pediatric offices. Half of participants were white, 26% were black and 24% were Hispanic.

Blacks tended to mature earlier than whites and Hispanics, the researchers found, showing significantly earlier mean ages for stage 2 to 4 genital development and stage 2 to 4 pubic hair growth. Mean ages of onset for Tanner stage 2 genital development was 9.14 for blacks, 10.04 years for Hispanics and 10.14 for whites. For stage 2 pubic hair, the mean ages of onset were 10.25, 11.43 and 11.47, respectively.

Testicular volumes of ≥3 mL — a measure indicative of central pubertal take-off — were achieved at a mean age of 9.71 among blacks, 9.63 for Hispanics and 9.95 for whites, with the corresponding ages of 11.75, 11.29, and 11.46 for ≥4 mL.

The average ages for reaching sexual maturity, as indicated by Tanner stage 5, ranged from 15.51 to 15.89, with no differences between the racial/ethnic groups.

“The causes and public health implications of this apparent shift in U.S. boys to a lower age of onset for the development of secondary sexual characteristics in U.S. boys needs further exploration,” the researchers wrote.

They noted that the study population may not be representative of the overall U.S. population, and that participants’ age estimates lack precision, as researchers were unable to collect information birth dates because of privacy concerns.


  1. Herman-Giddens M et al. Pediatrics. 2012; doi: 10.1542/peds.2011-3291.