Puberty is the stage of development when a child’s body gradually changes into a sexually mature adult body. It involves changes in the reproductive organs, hormones, bones, muscles, skin, brain, and body composition. It also brings changes that are less visible, including shifts in emotions, sleep patterns, and the way a person experiences their growing independence.
Puberty does not happen all at once, and there is no single age when it begins or ends. The timing, sequence, and pace vary considerably from person to person. Most of the changes are a normal part of human development.
How puberty begins
Puberty starts when the brain activates a hormone system called the hypothalamic-pituitary-gonadal axis. The hypothalamus, a region of the brain, begins releasing pulses of a hormone called gonadotropin-releasing hormone (GnRH). This signals the pituitary gland to release two other hormones: luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
LH and FSH stimulate the gonads—the ovaries or testes—to become more active. The ovaries produce increasing amounts of estrogen and the testes produce increasing amounts of testosterone. These sex hormones drive many of the physical changes associated with puberty.
The adrenal glands also become more active during this period. They produce hormones called adrenal androgens, which contribute to the development of pubic and underarm hair and changes in body odor.
When puberty happens
Puberty commonly begins during late childhood or early adolescence, but normal timing varies. Some people start earlier and others later. Puberty also does not necessarily progress at the same speed in every part of the body.
In girls, the first noticeable changes often include breast development and the appearance of pubic hair. In boys, enlargement of the testicles is commonly one of the earliest physical signs, followed later by growth of the penis and other changes. These are general patterns rather than rigid rules, and individual development can follow a different sequence.
A person’s genetics, overall health, nutrition, body composition, and other biological factors can influence when puberty begins and how it progresses.
The major physical changes
Growth speeds up
One of the most noticeable features of puberty is the growth spurt. The body begins growing more quickly, with changes in height, weight, bones, and muscle.
Growth does not occur evenly. Hands and feet may grow rapidly before the rest of the body catches up, sometimes making a teenager temporarily look or feel awkward. The limbs and trunk also grow at different rates.
Eventually, growth slows as the growth plates at the ends of the long bones gradually close. Sex hormones, together with growth hormone and other hormonal signals, play an important role in this process.
The reproductive system matures
The reproductive organs grow and become capable of adult reproductive function.
In people with ovaries, the ovaries mature and begin releasing eggs as ovulation becomes established. The uterus and other reproductive structures also develop. Menstruation begins as part of this process, although the menstrual cycles during the first years after the first period may be irregular.
In people with testes, the testes enlarge and begin producing increasing amounts of testosterone and sperm. The penis and other reproductive structures grow, and erections and ejaculation may occur.
These changes do not happen on a fixed timetable. Reproductive maturity develops gradually rather than appearing on one particular day.
Body hair changes
Hair growth increases in areas that were previously relatively hairless. Pubic hair usually develops around the genitals, and underarm hair commonly appears later.
Many people also develop more noticeable facial or body hair. The amount and distribution vary substantially among individuals and are strongly influenced by genetics and hormones.
Skin and sweat glands change
Puberty increases the activity of oil-producing sebaceous glands in the skin. This can make the skin oilier and contribute to acne, particularly on the face, chest, shoulders, and back.
Sweat glands also become more active. Changes in the composition of sweat and increased activity of certain glands contribute to stronger body odor. Regular bathing, clean clothing, and deodorant or antiperspirant can help manage it.
Acne is not caused by poor hygiene. It results largely from hormonal changes that increase oil production and affect the way skin cells and hair follicles behave.
The body’s shape changes
Hormones influence how muscle, fat, and bone develop. On average, testosterone promotes greater increases in muscle mass and bone size, while estrogen contributes to changes in breast development, body-fat distribution, and the maturation of bones.
There is substantial natural variation, however. Puberty does not produce one universal body shape, and differences in height, muscle, breast development, hips, body hair, and body-fat distribution are normal.
What happens to the voice?
The voice box, or larynx, grows during puberty, and the vocal cords become longer and thicker. These changes lower the voice.
The change is particularly pronounced in boys, although everyone’s voice changes to some degree. During the period when the larynx is changing, the voice may temporarily crack or shift unpredictably.
Voice development continues as the structures involved in producing sound mature.
What happens in the brain?
Puberty is also a period of substantial brain development. The brain continues refining its connections and systems involved in planning, decision-making, emotional regulation, learning, and social behavior.
This does not mean that teenagers suddenly become irrational or that their brains are incapable of responsible decisions. Rather, different brain systems mature on different schedules. Reward, emotion, social information, and long-term planning can therefore interact in changing ways during adolescence.
Sleep patterns also commonly shift. Many adolescents naturally begin feeling sleepy later at night and prefer to wake later in the morning. At the same time, school schedules and other demands may limit how much sleep they actually get.
Emotional and social changes
Hormonal changes are only part of the psychological changes of puberty. Adolescence also brings new social experiences, greater independence, changing relationships, and increased awareness of identity and sexuality.
Mood may fluctuate, and feelings can sometimes seem unusually intense. Increased sensitivity to social approval, embarrassment, attraction, or rejection is also common.
Puberty itself does not automatically cause mental health problems or explain every emotional change. A young person’s environment, relationships, stress, personality, sleep, and other factors also matter.
Puberty is different for everyone
There is a wide range of normal development. Two people of the same age can be at very different stages of puberty, and both can be developing normally.
Some changes happen in a predictable sequence, but the timing between them varies. One person may grow rapidly before developing much body hair, while another may develop body hair earlier. Menstruation may begin after other visible changes have already occurred. Facial hair, breast development, height, muscle growth, and other traits can continue changing for years.
Comparing development with friends or classmates can therefore create unnecessary worry. Puberty is a process, not a race.
When puberty may need medical attention
Most variations in puberty are harmless, but unusually early, unusually late, or stalled development can sometimes indicate an underlying medical issue.
Puberty that begins much earlier than expected may be considered precocious puberty. Delayed puberty can also have several possible causes, ranging from normal variation and family patterns to nutritional, hormonal, genetic, or other medical conditions.
A healthcare professional can assess growth patterns, physical development, family history, and, when appropriate, hormone levels or other tests. Medical evaluation is especially useful when development appears to stop progressing, when growth is markedly different from a person’s previous pattern, or when a child or adolescent has other concerning symptoms.
Puberty is ultimately a coordinated biological transition driven by hormones and influenced by genetics, health, and the environment. Its changes can be dramatic, but they unfold gradually, and considerable variation is normal. Understanding that variability can make the physical and emotional changes of adolescence easier to recognize as part of a larger process of human development.
