The changes that occur only in males during puberty are testicular and penile growth, sperm production, voice deepening caused by laryngeal growth, development of an Adam’s apple, and facial hair. While both sexes experience hormonal shifts, growth spurts, and new body hair in places like the underarms, these specific changes are driven by testosterone and happen exclusively in boys.
Testicular and Penile Growth
The very first sign of male puberty is enlargement of the testes and scrotum. This typically begins between ages 9 and 14. Clinically, puberty is considered underway once testicular volume reaches about 4 milliliters, roughly the size of a large grape. Before puberty, the testes are smaller than that threshold.
As the testes grow, they ramp up testosterone production. Testosterone levels in boys rise dramatically across puberty, from under 20 nanograms per deciliter in childhood to a range of 300 to 950 by late adolescence. That hormonal surge drives nearly every other male-specific change. The penis begins to grow in both length and width after the testes have already started enlarging, usually a year or so into the process.
Sperm Production
Boys begin producing sperm at a median age of about 13.4 years, though it can start as early as 11.7 or as late as 15.3. This milestone, called spermarche, can happen surprisingly early in puberty, sometimes before much pubic hair has appeared and when the testes have only grown slightly from their prepubertal size. It marks the biological onset of male fertility.
Along with sperm production comes the possibility of ejaculation, including involuntary ejaculation during sleep. These “wet dreams” (nocturnal emissions) are a normal part of male puberty and tend to become less frequent over time.
Voice Deepening and the Adam’s Apple
Testosterone causes the larynx, or voice box, to grow significantly larger in boys. The vocal folds gradually increase in length and mass throughout puberty, which lowers the pitch of the voice. This process isn’t instant. Most boys experience a period of voice “cracking” or unpredictable pitch changes as the vocal folds are actively growing and the muscles controlling them adapt.
The same growth that deepens the voice also creates the Adam’s apple. The thyroid cartilage, which forms the front wall of the larynx, angles forward more sharply in males. Research using CT imaging shows that the angle of this cartilage stays relatively flat in females (about 170 degrees) but narrows in males to roughly 161 degrees, pushing it outward and creating that visible bump on the throat. Girls experience some laryngeal growth too, but not enough to produce a noticeable prominence or a major voice change.
Facial Hair Development
Both boys and girls grow new body hair during puberty, particularly in the underarms and pubic area. Facial hair, however, is exclusive to male puberty. It follows a predictable sequence that stretches over several years. The first hairs usually appear at the corners of the upper lip around ages 11 to 12. By 16 or 17, the mustache area fills in and hair begins growing along the sideburns and below the lower lip. A full beard, covering the cheeks and jawline, typically doesn’t develop until the late teens or early twenties, and some men never achieve full coverage.
Muscle Mass and Body Composition
Both sexes gain muscle during puberty, but the degree of change in males is far greater. Testosterone is a potent driver of lean muscle growth, particularly in the upper body and shoulders. By the end of puberty, young men carry substantially more muscle mass relative to body fat compared to young women. This divergence is one of the reasons average strength differences between the sexes widen sharply during adolescence. Girls gain muscle too, but estrogen favors fat deposition in the hips and thighs rather than the pronounced upper-body muscle development testosterone promotes.
Changes That Happen in Both Sexes
It helps to know what isn’t male-specific, since these shared changes sometimes get confused with male-only ones. Both boys and girls experience growth spurts, underarm and pubic hair, increased sweating and body odor, acne, and emotional shifts driven by hormonal changes. Both sexes also develop broader hips or shoulders to varying degrees, though the proportions differ. The key distinction is that testicular growth, sperm production, voice deepening, the Adam’s apple, and facial hair are biologically exclusive to male puberty.