During puberty, hormonal signals activate the reproductive system and produce progressive physical maturation. The hypothalamus begins releasing gonadotrophin-releasing hormone in a pulsatile manner, stimulating the pituitary gland to release luteinising hormone and follicle-stimulating hormone. These hormones activate the ovaries or testes, increasing production of oestrogen, progesterone, testosterone and other reproductive hormones. At the same time, adrenal androgen production increases. The resulting endocrine changes affect reproductive organs, bones, muscles, skin, hair, voice and body composition. Puberty is therefore a coordinated developmental process rather than a single physical event.
In girls, ovarian activity increases and oestrogen plays a major role in breast development, growth of the uterus and vagina, changes in the distribution of body fat and maturation of the reproductive system. Pubic and underarm hair develops through contributions from adrenal and gonadal hormones. The growth spurt generally occurs earlier than in boys on average. Menstruation, or menarche, usually occurs after other pubertal changes have already begun and does not necessarily indicate that every menstrual cycle is immediately ovulatory. Early cycles can be irregular while the hypothalamic-pituitary-ovarian system matures.
In boys, rising luteinising hormone stimulates Leydig cells in the testes to produce testosterone, while follicle-stimulating hormone and testosterone support sperm production through Sertoli-cell function. The testes enlarge early in male puberty, followed by progressive enlargement of the penis and development of other reproductive structures. Pubic and facial hair increases, the voice generally deepens as the larynx enlarges, and muscle mass tends to increase. Spermatogenesis develops progressively, and ejaculated semen eventually contains mature sperm. The pace and extent of these changes vary substantially between individuals.
Both sexes experience a growth spurt during puberty. Growth hormone secretion and insulin-like growth factor 1 interact with sex steroids to accelerate bone and tissue growth. The hands and feet may grow noticeably before the trunk catches up, producing temporary changes in body proportions. Later, sex steroids stimulate maturation of the growth plates, and the epiphyseal plates eventually fuse, ending longitudinal bone growth. Peak bone mass is also accumulated during adolescence, making adequate nutrition, physical activity and sufficient calcium and vitamin D important components of healthy skeletal development.
Skin and sweat glands change significantly. Sebaceous glands become more active, increasing sebum production and making the skin oilier. This contributes to the increased frequency of acne during adolescence because sebum interacts with follicular keratinisation, Cutibacterium acnes and inflammation. Apocrine sweat glands also become functionally active, contributing to changes in body odour. Increased sweating does not necessarily indicate poor hygiene; it reflects normal glandular maturation. Regular washing and appropriate skin care can manage odour and oiliness, while persistent or severe acne can require medical treatment.
Body hair distribution changes during puberty. Pubic and axillary hair commonly develops, and facial and chest hair can increase in many males. The amount, thickness and distribution of hair are strongly influenced by genetics and androgen sensitivity, so there is considerable normal variation. Hair development does not follow exactly the same schedule in everyone and is not a reliable measure of overall maturity on its own. Changes in skin pigmentation, genital pigmentation and other physical characteristics can also occur as hormone levels change.
The reproductive system becomes increasingly functional during puberty, but maturation is gradual. In females, menstrual cycles and ovulation become established progressively, while in males sperm production becomes active. Puberty also changes sexual development and can increase sexual interest, although the timing and intensity of these experiences vary widely. Reproductive capacity emerging during puberty means that pregnancy becomes biologically possible before adolescence has ended, which makes accurate age-appropriate education about contraception, consent and sexually transmitted infections important. Biological fertility and emotional or social readiness are separate concepts.
Puberty also occurs alongside continuing brain and psychosocial development. Adolescents may experience changes in sleep patterns, emotional responses, social relationships and independence. These changes reflect interactions among endocrine maturation, ongoing brain development and the social environment rather than being caused solely by reproductive hormones. The timing of puberty can vary substantially, and temporary asymmetries or irregularities in development can be normal. However, very early onset, absent or stalled progression, severe growth abnormalities or other concerning symptoms can warrant medical assessment because endocrine disorders, chronic illness, nutritional problems or other conditions can sometimes disrupt normal pubertal development.
