Puberty is the developmental period during which the body changes from childhood towards biological sexual maturity. There is no single age at which puberty begins because timing varies considerably between individuals, but in general it begins between about 8 and 14 years of age. The first signs result from activation of the hypothalamic-pituitary-gonadal axis, a hormonal communication system involving the brain, pituitary gland and gonads.
The hypothalamus begins releasing gonadotropin-releasing hormone in pulses, stimulating the pituitary gland to produce luteinising hormone and follicle-stimulating hormone. These hormones stimulate the ovaries or testes, increasing production of sex steroids such as oestrogen and testosterone. Puberty therefore represents a coordinated endocrine process rather than a single physical event.
The earliest visible manifestations differ between individuals and are not necessarily the same in every sex. In many children, one of the earliest changes is adrenarche, involving increased adrenal androgen production, which can contribute to pubic or underarm hair, body odour and changes in skin oiliness. Gonadarche refers more specifically to activation of the ovaries or testes. In children with ovaries, breast development is commonly an early sign, followed later by pubic hair, growth acceleration and eventually menstruation. In children with testes, enlargement of the testicles is generally an early sign, followed by penile growth, pubic hair, voice deepening and increasing muscle mass. These sequences overlap and vary, so individual development does not necessarily follow a rigid timetable.
Puberty is controlled by feedback relationships between reproductive hormones and the brain. Gonadotropin-releasing hormone stimulates pituitary secretion of luteinising hormone and follicle-stimulating hormone, which act on the gonads. The ovaries respond by producing oestrogens and progesterone and developing ovarian follicles, while the testes produce testosterone and support sperm production. Sex steroids also act on tissues throughout the body, producing breast development, changes in body composition, growth of reproductive organs, bone maturation and other secondary sexual characteristics. Growth hormone and insulin-like growth factor 1 contribute to the pubertal growth spurt, while adrenal hormones contribute to hair and skin changes. The eventual reduction of growth-plate activity by sex steroids contributes to the attainment of adult height.
Puberty begins when the underlying endocrine system becomes sufficiently active, but its timing is influenced by genetics, nutrition, body composition, general health and environmental factors. Family patterns are important, so children often enter puberty at ages broadly similar to those of close relatives. Adequate energy availability is also necessary for normal reproductive development. Significant undernutrition or some chronic illnesses can delay puberty, whereas certain medical conditions can cause unusually early activation of the reproductive hormonal system.
Body composition and metabolic signalling, including signals associated with energy stores, interact with reproductive endocrine pathways. This explains why puberty cannot be predicted accurately from chronological age alone and why two otherwise healthy children of the same age can be at substantially different stages of development.
In children with ovaries, menstruation usually occurs after other pubertal changes have already begun rather than marking the beginning of puberty. The first menstrual period is called menarche and commonly occurs around age 12, although earlier and later onset can be normal. Early menstrual cycles are frequently irregular because the hormonal system controlling ovulation may take time to mature. Ovulation does not necessarily occur consistently from the beginning of menstruation, so cycle length and bleeding patterns can vary considerably during the first years. Most girls are having more regular periods by approximately 16 to 18 years, although individual patterns differ.
Puberty can begin earlier or later than the usual range without necessarily indicating disease. The NHS considers signs beginning before age 8 potentially indicative of early puberty and absence of puberty by age 15 potentially indicative of delayed puberty, although clinical assessment depends on the individual pattern and circumstances. Causes of unusually early puberty can include premature activation of the central reproductive hormone pathway or, less commonly, hormone production from another source. Delayed puberty can result from constitutional variation, inadequate nutrition, chronic disease, endocrine disorders or problems affecting the reproductive organs or pituitary-hypothalamic system. A clinician can assess growth, physical development, family history and, where appropriate, hormone concentrations, bone age or other investigations.
Puberty is sometimes incorrectly treated as a sudden event that begins on a particular birthday, but it is actually a gradual developmental process extending over several years. Its physical, hormonal and psychological components do not necessarily progress simultaneously. Acne, increased sweating, body odour, hair growth and changes in skin oiliness can appear before or alongside reproductive development. Emotional and behavioural changes may occur during adolescence, but they cannot be attributed solely to puberty because social, psychological, educational and environmental factors also have major effects. Puberty also does not mean that every aspect of biological maturation is complete; brain development, bone maturation and reproductive maturation continue throughout adolescence.
Understanding the normal range of puberty is particularly important when interpreting menstrual development. Menstruation requires sufficient maturation of the reproductive endocrine system, so the timing of a first period is influenced by when puberty began and how quickly it progresses. Persistent concerns about very early development, absent development, markedly delayed development, or significant growth abnormalities warrant medical assessment rather than comparison with peers. Pubertal timing also has implications for bone health, reproductive development and psychological wellbeing. The central principle is that normal puberty has a broad range of timing and sequence, while significant deviation from expected patterns can sometimes provide an early clue to an endocrine, nutritional or other medical condition.
