What are the main stages of male puberty?
Executive summary
Male puberty is a multi-year biological process usually described by five Tanner stages (sexual maturity ratings) that track genital and pubic hair development from prepubertal through adult maturity [1]. It is initiated by hormonal signaling from the brain — the hypothalamus and pituitary — which stimulates testicular growth, testosterone production and the cascade of physical and behavioral changes characteristic of adolescence [2][3].
1. The hormonal trigger: GnRH, LH, FSH and testosterone
Puberty begins when the hypothalamus increases pulsatile release of gonadotropin‑releasing hormone (GnRH), prompting the pituitary to secrete luteinizing hormone (LH) and follicle‑stimulating hormone (FSH), which in turn stimulate the testes to enlarge and to produce testosterone and sperm‑supporting activity in Leydig and Sertoli cells [2][3].
2. Stage I — prepubertal baseline
Tanner stage I is the prepubertal state with child‑like genitalia, testicular volumes typically less than about 4 mL, and no pubic hair; there are no obvious secondary sexual characteristics at this stage [1][4].
3. Stage II — gonadarche: first visible signs
Tanner stage II marks gonadarche and is defined by a noticeable increase in testicular volume (≥4 mL or long axis ≥2.5 cm) and initial thinning and reddening of the scrotum, with sparse, lightly pigmented pubic hair beginning to appear; this is widely recognized as the start of physical puberty in boys [1][5].
4. Stage III — rapid genital growth and peak height velocity
During Tanner stage III the penis and testes continue to grow more rapidly, pubic hair becomes darker and coarser, and boys typically experience peak height velocity — the steepest part of their adolescent growth spurt [1][5].
5. Stage IV — continued maturation, spermarche and voice change
Stage IV shows further enlargement of the penis (length then width), continued testicular growth toward adult size, adult‑type pubic hair that has not yet spread to the medial thigh, and spermarche (the onset of sperm production and commonly the first ejaculation, often about a year after penile growth begins); voice deepening and temporary gynecomastia can also appear in these middle stages [6][1][7].
6. Stage V — adult phenotype and reproductive maturity
Tanner stage V represents adult genitalia and pubic hair distribution with testicular volumes typically ≥20 mL and attainment of adult hormone levels and most adult height, although muscular development can continue beyond completion of Tanner staging [4][8].
7. Typical timing and wide normal variation
On average male puberty begins later than female puberty, often starting between about ages 9–14 or more commonly around 10–16 depending on the source, and the entire process usually lasts roughly 2–5 years, but there is substantial individual and population variability influenced by genetics, nutrition and environment [9][10][11].
8. Common experiences and temporary phenomena
Common and transient features include increased sweating and body odor, acne from hormonal changes, spontaneous erections and nocturnal emissions (wet dreams), and temporary breast tissue enlargement (pubertal gynecomastia), which is usually benign though sometimes distressing [7][12][6][1].
9. When development falls outside expected patterns
Clinical attention is advised if there are signs of early or delayed puberty — for example boys who have not reached Tanner stage II by about age 14 may warrant evaluation — because central nervous system causes, endocrine disorders, nutritional factors or genetic conditions can alter timing and progression [1][3].
10. Limitations and differing emphases in sources
Sources converge on the five‑stage Tanner framework and the hormonal cascade but differ in precise age ranges and emphasis — some stress cultural and racial timing differences, others focus on behavioral or psychosocial changes — and reporting here reflects those variations while noting that exact ages and durations are probabilistic rather than deterministic [13][14][15].