Puberty

Puberty is the phase of development between childhood and complete, functional maturation of the reproductive glands and external genitalia. Puberty typically starts with gonadarche, which is the stimulation of sex hormone production through the hypothalamic-pituitary-adrenal axis. Although there is considerable variation between individuals, puberty typically begins around the age of 11 in girls and 13 in boys. Physical changes during puberty include the development of secondary sexual characteristics (breast development, male genitalia development, and pubic hair growth), which can be measured using the sexual maturity rating (SMR), and the adolescent growth spurt. Factors affecting the onset and progression of puberty include genetics, environmental factors, race and ethnicity, and nutrition.

Disorders of puberty, such as precocious puberty and delayed onset of puberty, are covered separately.

• Adrenarche: activation of adrenal androgen production, which precedes other pubertal changes and leads to development of axillary and pubic hair, body odor, and acne
• Gonadarche: activation of reproductive glands by the pituitary hormones FSH and LH
• Thelarche: onset of breast development
• Pubarche: onset of pubic hair growth
• Menarche: onset of menstrual bleeding

Normal pubertal timing and progression

The age of pubertal onset varies, but the sequence of changes that occur is consistent.

Hormonal changes in both boys and girls ^[1]

• Adrenarche typically precedes the onset of puberty. ^[2]
• Puberty starts with gonadarche, which leads to development of secondary sexual characteristics.
• Adrenarche continues during puberty and contributes to physical changes (e.g., pubarche, axillary hair).

Physical changes in girls

Changes typically occur in the following order:^[1]

1. Thelarche: onset at age 8–12 years (average 10 years)
2. Adolescent growth spurt: peak growth velocity between 11–12 years of age
3. Pubarche: variable age of onset, ; but typically after thelarche ^[3]
4. Menarche: 2.5 years after onset of thelarche (range: 9–15 years of age; average: 12.5 years of age) ^[1][4]

Physical changes in boys

Changes typically occur in the following sequence. ^[1]

1. Testicular enlargement; (testicular volume ≥ 4 mL and/or length ≥ 2.5 cm): onset at 9.5–14 years of age (average 11.5 years of age)
2. Pubarche: Age of onset varies. ^[3]
3. Adolescent growth spurt: peak growth velocity at 13–14 years of age

The first visible sign of puberty in boys is testicular enlargement, while in girls it is breast development. ^[1]

Factors affecting timing and progression of puberty

• Genetics ^[5]
• Environmental and social factors (e.g., family stress) ^[6]
• Race and ethnicity ^[6][7]
• General health (e.g., nutritional status, body weight) ^[8][9]
  • Undernutrition and excessive exercise are associated with delayed onset of puberty.
  • Obesity is associated with early puberty (obesity-related precocious sexual development). ^[10]
    • The exact association and mechanism are not well defined. ^[10]
    • Proposed central mechanism: Obesity → ↑ leptin→ ↑ GnRH pulsatility → ↑ production of gonadotropins and sex hormones → early development of secondary sexual characteristics. ^[11]
    • Proposed peripheral mechanism: Obesity → insulin resistance and compensatory hyperinsulinemia → ↑ sex hormone production. ^[10]
• For other causes of abnormal pubertal progression, see "Precocious puberty" and "Delayed onset of puberty."

Secondary sexual characteristics are physical features that develop during puberty, including breasts, male genitalia, and pubic hair.

Sexual maturity rating (Tanner staging) ^[1]

• A scale used to assess the development of secondary sexual characteristics
  • Breast development (girls)
  • Genital development (boys)
  • Pubic hair (boys and girls)
• An SMR of 1 corresponds to prepubertal appearance; higher numbers indicate further sexual maturation.

Girls

Boys

• Physiologic leukorrhea ^[12]
  • Thin, white, odorless vaginal discharge caused by the effect of estrogen on vaginal mucosa
  • Can begin during the 12 months before menarche
• Pubertal gynecomastia ^[13]
  • Occurs in ∼ 50% of boys
  • Onset typically during SMR stage 3–4
  • Further evaluation indicated if not resolved within 18–24 months of onset ^[1]
• Adolescent growth spurt ^[1]
  • Linear growth (↑ growth in trunk and limbs) during adolescence occurs at ∼ 5 cm/year from 4 years of age to puberty. ^[1]
  • Peak height velocity (assessed using growth charts) can occur two years earlier in girls than boys.^[4]
    • Girls: peak velocity between SMR 2 and 3 (age 11–12 years)
    • Boys: peak velocity between SMR 3 and 4 (age 13–14 years)
  • Generally lasts ∼ 2 years; girls complete linear growth around 15 years of age and boys around 17 years of age. ^[1]
• Bone growth: accelerated during puberty
  • Increase in bone length precedes attainment of peak bone mass and strength.^[14][15]
  • Influenced by sex hormones
• Body weight and body composition during adolescence ^[16]
  • Boys: initial ↓ body fat (early puberty) → ↑ lean body mass (late puberty)
  • Girls: gradual increase in body fat with increased distribution in the lower body
  • Affected by nutritional status
• Dermatologic changes ^[3]
  • Activation of the adrenal cortex → pubertal hormonal fluctuation → ↑ sebum secretion and excessive sweating → skin and hair changes
  • Manifestations include acne vulgaris, axillary body odor, seborrheic dermatitis, and thicker terminal hairs (e.g., on face, body).
• Other changes
  • Voice changes: deepening of the voice, increased larynx size in boys ^[2]
  • Myopia: due to increased axial growth of the eye during rapid growth of adolescence ^[8]
  • Clinical features of iron deficiency anemia: may develop in post-menarchal girls. ^[17]

Early menstrual cycles may be irregular and anovulatory due to immaturity of the hypothalamic-pituitary-gonadal axis. ^[2]