Recognizing puberty onset in boys

A look at the clinical features of puberty in boys to help determine where patients are in the process.

Although mood changes might be the first sign parents notice when it comes to onset of male puberty, there are several clinical features pediatricians can use to gauge where their patients are in this process.

Katherine Kutney, MD, a pediatric endocrinologist and assistant professor in the field at Rainbow Babies and Children’s Hospital in Cleveland, Ohio, said for both boys and girls, the entire process is triggered by the activation of the hypothalamic-pituitary-gonadal axis. For boys, this causes testicular growth, which is the first clinical sign that a male has entered central puberty.

The first clinical sign that this process has begun is an increase in testicular volume of 3 mL or more. An increase in height will occur when testicular volume reaches 10-12 mL, Kutney said. Males who have reached this testicular volume without a growth spurt may be cause for concern, she added.

Alongside of central puberty and the increase of testicular volume, another process is underway. This process, adrenarche, begins with the production of adrenal androgens. Commonly referred to as male sex hormones, these spur the growth of pubic hair, axillary hair, and acne throughout puberty.

Kutney said although central puberty and adrenarche often occur together, these 2 processes are regulated separately, and it’s possible to have one without the other.

This is especially true when puberty begins earlier than the normal range for boys, which is between 9 and 14 years of age, or at age 11 years on average. Studies have suggested that girls are entering puberty earlier than previous generations, but whether the same is true for boys is still in question.

A 2012 report in Pediatrics found that boys were beginning testicular volume increases and pubic hair growth between 6 months and 2 years earlier than in past studies.1 Many of the studies the male average had been based on involving only white, European boys. The 2012 study took several ethnicities into consideration, noting earlier genital and public hair development in African-American boys compared to white and Hispanic boys.

The study notes its limitations based on the fact that earlier studies generally didn’t include non-white boys. However, in looking at sexual development in white boys alone, the 2012 study found that white boys were entering Stage 2 genital growth on the Tanner scale about 1.5 years earlier—from 10.14 years in the 40-year-old British study to 11.6 years in the 2012 US study.

A more recent study, published in JAMA Pediatrics in 2019, appears to confirm the earlier entry of boys into puberty.2 The 2019 study revealed that a number of factors may be to blame for this shift, but points to increases in childhood body mass index as at least a partial cause.

Although the exact cause prompting earlier puberty in boys is yet to be determined, experts still agree that the Tanner Staging, or the Sexual Maturity Rating scale, is still the most reliable and objective classification system for determining onset and progress through puberty. The system takes into account both genital and pubic hair development to determine staging.

For boys and girls, Stage 1 of the Tanner scale designates the pre-puberty period and Stage 5 signifies full sexual maturity. A clinical reference of the Tanner Stages for boys can be found below.3

Tanner Staging for Males

Pubic Hair

  • Stage 1: No hair
  • Stage 2: Light, downy hair
  • Stage 3: Thicker, darker (terminal) hair begins to develop
  • Stage 4: Terminal hair covers the entire triangle of the pubic region
  • Stage 5: Terminal hair covers the entire triangle of the pubic region and extends past the inguinal crease to the thigh

Genitalia scale

  • Stage 1: Testicular volume of less than 4 mL, or a long axis of less than 2.5 cm
  • Stage 2: Testicular volume of 4-8 mL, or a long axis measuring between 2.5 and 3.3 cm long
  • Stage 3: Testicular volume of 9-12 mL, or a long axis measuring between 3.4 and 4 cm long
  • Stage 4: Testicular volume of 15-20 mL, or a long axis measuring between 4.1 and 4.5 cm long
  • Stage 5: Testicular volume of 20 mL or more, or a long axis measuring more than 4 cm long

References

1. Herman-Giddens, et al. Secondary sexual characteristics in boys: data from the pediatric research in office settings network. Pediatrics. 2012;130(5): e1058-e1068. doi: 10.1542/peds.2011-3291

2. Ohlsson C, Bygdell M, Celind J, et al. Secular trends in pubertal growth acceleration in Swedish boys born from 1947 to 1996. JAMA Pediatr. 2019;173(9):860–865. doi:10.1001/jamapediatrics.2019.2315

3. Emmanuel M, Bokor BR. Tanner Stages. StatPearls Publishing. 2021.