Puberty and sexual development

• Puberty is the series of hormonal and physical changes that turns a child into a fertile adult; in most healthy children it starts between 8 and 13 years in girls and 9 and 14 years in boys (some sources describe the window as 8 to 12 years in girls). ^{[1] [6]}
• The first reliable sign is breast budding (thelarche) in girls and testicular enlargement to 4 mL in boys; pubic hair alone is not enough because it can come from the adrenal glands. ^[1]
• Pubertal development is staged clinically from 1 to 5 with the Marshall–Tanner scales; progression, height velocity and bone age matter as much as the calendar age.
• Puberty is classified as precocious when it starts before 8 years in girls or 9 years in boys, and delayed when there are no pubertal signs by about 13 years in girls or 13 to 14 years in boys (some sources use 13 years for both). ^[1][6]
• Most delayed puberty is constitutional delay; most precocious puberty in girls is central (hypothalamic–pituitary–gonadal driven) and treated with long-acting GnRH analogues. ^[6]
• Pubertal gynaecomastia is common, benign and self-limiting in most adolescent boys.

By the end of this page you should be able to:

1. Describe the hormonal machinery that restarts puberty and the normal sequence of pubertal events in girls and boys.
2. Stage pubertal development with the Tanner scales and use normal timing windows to recognise early and late puberty.
3. Distinguish central from peripheral precocious puberty, and constitutional delay from pathological delayed puberty, using their mechanisms and laboratory patterns.
4. Plan the evaluation of a child with puberty concerns, including bone age, LH and FSH (basal and stimulated), gonadal imaging and brain imaging.
5. Choose and explain GnRH-analogue treatment for central precocious puberty, and counsel families about its benefits and limits.
6. Recognise and manage the common benign problems of mid-puberty: premature thelarche, premature adrenarche and pubertal gynaecomastia.
7. Outline safe practice and sensible expectations in low-resource settings.

Puberty is not a switch; it is a programme. The child already carries the blueprint before birth, and the programme only needs to be restarted after years of childhood quiescence. When it restarts on time the result is a healthy adult with fertility, full height and sexual function. When it starts too early or too late the cause may be a serious disorder, and the consequences can include short adult stature, psychological distress and, rarely, a missed brain or endocrine tumour.

The first job of the clinician is therefore not to treat, but to classify: is this normal, early, or late, and if abnormal is the drive coming from the brain (central) or from the gonads and adrenals (peripheral)? Almost everything else follows from that.

Puberty is the biological process that produces secondary sexual characteristics, accelerates growth, and ends in reproductive capacity. It is driven by the reactivation of the hypothalamic–pituitary–gonadal (HPG) axis: pulsatile gonadotropin-releasing hormone (GnRH) from the hypothalamus stimulates pituitary luteinising hormone (LH) and follicle-stimulating hormone (FSH), which stimulate the testes or ovaries to make sex steroids. ^[1]

Precocious puberty is the appearance of secondary sexual characteristics before 8 years of age in girls and 9 years in boys in most classifications (one recent review uses 7.5 years for girls; guidelines differ).^[2][6] Girls with breast budding at 7 to 8 years may first be observed for 4 to 6 months (Endocrine Society 2026). ^[7]

Delayed puberty is the absence of pubertal signs by an age 2 standard deviations above the mean: no breast development by about 13 years in girls and no testicular enlargement at or above 4 mL by about 13 to 14 years in boys (some sources use about 13 years for both).^[1][6]

Central precocious puberty (CPP) is gonadotropin-dependent: the HPG axis has been reactivated early. It is about ten times more common in girls than in boys, and most girls with it have no identifiable cause. In boys early onset is more often linked to an underlying brain lesion, although contemporary data show that lesions are found in only about 6 to 8% of otherwise uncomplicated cases.^{[3] [6]}

Peripheral precocious puberty (PPP) is gonadotropin-independent. Sex steroids reach the tissues from the gonads, the adrenals, or an external source, without central activation. Causes include McCune–Albright syndrome (mosaic GNAS activation with ovarian cysts, polyostotic fibrous dysplasia and café-au-lait spots), congenital adrenal hyperplasia, adrenal or gonadal tumours, hCG-secreting germ cell tumours, and exogenous sex steroids. PPP may be isosexual (consistent with biological sex) or heterosexual (virilisation of girls or feminisation of boys).^[6]

Constitutional delay of growth and puberty (CDGP) is the commonest cause of late puberty in both sexes. It is a familial, self-limited delay of the HPG axis and is a diagnosis made only after pathological causes have been excluded.

Delayed puberty is otherwise grouped by gonadotropin level:

• Hypergonadotropic hypogonadism — high LH and FSH from failed gonads. Congenital causes include gonadal dysgenesis, Turner syndrome in girls and Klinefelter syndrome in boys; acquired causes include chemotherapy or radiotherapy.
• Permanent hypogonadotropic hypogonadism — low LH and FSH from hypothalamic or pituitary disease: tumours, infiltrative disease, isolated GnRH deficiency (Kallmann syndrome, often with anosmia), combined pituitary hormone deficiency.
• Transient (functional) hypogonadotropic hypogonadism — a reversible slow maturation of the axis secondary to systemic illness, malnutrition, hypothyroidism, chronic disease (for example coeliac or inflammatory bowel disease), anorexia nervosa, or excessive training.^[1]

Precocious puberty as a whole affects girls far more often than boys. Reported incidences include roughly one in 5000 to one in 10000 girls in a US series, and 15 to 20 girls are affected for every boy in some series. Other series report around 0.2% of girls and under 0.05% of boys developing true precocious puberty, and in Denmark about 0.2% of girls and under 0.05% of boys.^[6] More recent national data give 55.9 per 100000 girls and 1.7 per 100000 boys in South Korea, and 37 per 100000 girls versus 0.46 per 100000 boys in Spain.^[6]

The age of onset has been falling slowly in many populations, probably through childhood obesity and environmental exposures. The COVID-19 lockdown accelerated the rise in referrals in several countries. Boys develop central precocious puberty about ten times less often than girls, but the incidence in boys has also been rising.^[3]

Delayed puberty is harder to count because definitions and ascertainment vary; constitutional delay alone is by far the commonest explanation in otherwise healthy adolescents.

The restart of puberty is governed by the balance between inhibitors and activators of GnRH neurons. Rare single-gene defects prove the point. Loss-of-function in MKRN3 and DLK1, both paternally expressed imprinted genes, is among the most common monogenic causes of familial central precocious puberty; gain-of-function changes in KISS1 and KISS1R remove the brakes instead.^[3][6] Syndromes associated with central precocious puberty include McCune–Albright-related GnRH-dependent disease when the hypothalamus is involved, neurofibromatosis type 1, tuberous sclerosis, syndromes such as Prader–Willi, Temple and Silver–Russell, and central nervous system lesions, which are more common in boys.^[6]

For most children, however, timing is polygenic and modulated by nutrition, adiposity, stress, sleep, adoption and exposure to endocrine-disrupting chemicals. Rapid weight gain in early childhood, longer screen time, short sleep and disrupted circadian rhythm are associated with earlier pubertal onset, while regular aerobic exercise and adequate sleep during childhood may help prevent early pubertal onset. Children born small for gestational age who show rapid catch-up growth can also enter puberty earlier.^[2][3]

Central precocious puberty is idiopathic in 75 to 90% of girls and 25 to 60% of boys, while identifiable brain or genetic causes are more common in boys.^[6]

The normal restart begins in the brain. Kisspeptin and neurokinin B neurons in the hypothalamic arcuate nucleus increase pulsatile GnRH secretion. GnRH pulses act on pituitary gonadotrophs, which release LH and FSH in pulses; these reach the gonads and stimulate sex steroid production (gonadarche). The first ovarian output visible clinically is breast development; the first testicular output visible clinically is testicular enlargement.

Adrenarche is a separate, earlier event. It begins around 6 years of age, when the adrenal zona reticularis begins making dehydroepiandrosterone sulfate (DHEAS). Adrenarche drives pubic and axillary hair, acne and body odour but does not depend on gonadal activation and does not mean fertility has begun. ^[1]

Oestrogen in girls produces breast development, uterine growth, a linear growth spurt and finally menarche, which typically occurs about 2 to 3 years after thelarche, usually between 12 and 13 years. Testosterone in boys produces testicular enlargement first, then penile growth, pubic hair, ejaculation, facial hair, voice break and a later growth spurt. In both sexes peak height velocity follows substantial sex steroid exposure, which is why excessive growth in mid-childhood with pubertal signs suggests precocious puberty and advanced bone age.^[1]

Bone age on a left hand and wrist radiograph is one of the most useful windows on this process. In central precocious puberty bone age advances faster than chronological age. The degree of advance helps to judge remaining growth potential and the likely benefit of treatment.^[6]

• First sign: breast development (thelarche), usually between 8 and 13 years (some sources describe 8 to 12 years). ^{[1] [6]}
• Pubic hair (pubarche) usually follows thelarche.
• Adrenarche begins around 6 years, several years before gonadarche.
• Menarche occurs 2 to 3 years after thelarche, most commonly between 12 and 13 years in many series and often with early cycles 21 to 45 days. ^[1]
• Ethnicity, body weight and stress shift timing by more than a year across some populations, so the child’s family pattern is an important reference.^[1]

• Pubertal onset usually between 9 and 14 years.
• First sign: testicular enlargement above 4 mL. Penile and scrotal changes follow, then pubic hair.
• Spermarche (first ejaculation) occurs at a mean age of about 13.5 years; voice break occurs in late puberty, around 13 years (studies report means from about 12.9 to 13.9 years). ^[1]
• Adrenarche begins around 6 years.
• The pubertal growth spurt begins once testicular volume reaches 8 to 10 mL.^[1]

Pubertal gynaecomastia is normal here, not a disease (see below).

• Girls may present with breast budding, rapid growth, body odour or vaginal bleeding.
• Boys may present with testicular enlargement, penile growth, nocturnal erections or sudden voice change. Boys are more likely than girls to have an organic cause and to need earlier brain imaging.
• Central precocious puberty is much more common than peripheral in girls (around 80% of precocious puberty overall is central).^[3][6]

• Girls: no breast bud by 13 years.
• Boys: testicular volume under 4 mL by 13 to 14 years (some sources use 13 years).
• Common accompaniments are short stature, a childlike body habitus, and psychological distress.
• Pubic hair is deliberately excluded as a criterion because it can be produced by adrenarche alone, without gonadal activation.^[1]

Parents often worry before the child does. Measuring the parents and siblings usually provides reassurance in constitutional delay.

• A unilateral or asymmetric mass in the scrotum suggests a testicular tumour or McCune–Albright-type autonomous activation rather than central precocious puberty.
• Short testis with disproportionately large penile size points towards androgen exposure without testicular activation.
• Breast budding in girls that does not progress over months suggests premature thelarche rather than true puberty.

Pubertal gynaecomastia is the appearance of glandular breast tissue in an adolescent boy. It occurs in roughly half to 70% of adolescent boys, peaks at 13 to 14 years (often Tanner genital stages 3 to 4), and resolves in 75 to 90% within 6 months to 1 or 2 years as the androgen to oestrogen ratio settles. It is caused by a transient excess of oestrogenic relative to androgenic effect and by pubertal activation of growth hormone and IGF-1 in breast tissue.^[5]

Key practical points:

• Distinguish true glandular tissue from pseudogynecomastia (fat), by palpating a disc of firm tissue behind the areola. ^[5]
• Observation and reassurance are the right management for physiological pubertal gynaecomastia. ^[5]
• Persistent, progressive, severe or unilateral glandular enlargement, or onset before puberty or in late adolescence, warrants evaluation for pathological causes such as medication effect, Klinefelter syndrome, hypogonadism, a hormone-secreting tumour, or drug exposure.^[5]

A small testis with pubic hair and penile growth suggests peripheral androgen exposure rather than central activation, which needs testicular enlargement above 4 mL. Vaginal bleeding with minimal breast development suggests McCune–Albright syndrome. Cafe-au-lait spots, thyroid, growth or mood disturbance point towards a syndrome or tumour.^[6]

These are common, usually benign variants that must not be labelled as puberty:

• Premature thelarche — breast tissue appears in a girl under 8 years without other pubertal signs, with normal growth velocity and bone age. It is usually self-limiting and regresses over months to years; only a small minority progresses to central precocious puberty. Monitoring is the right first approach.^[6]
• Premature adrenarche — axillary or pubic hair, acne or body odour before 8 years in girls or 9 years in boys, driven by adrenal androgens without HPG activation. Bone age may be mildly advanced. It is usually benign but warrants monitoring, as affected children are at higher risk of later true precocious puberty and of polycystic ovary-related features.^[6]

The aim is to confirm that puberty has started, determine whether it is too early or too late, and find the cause.

1. Bone age (left hand and wrist radiograph) using Greulich and Pyle or Tanner–Whitehouse 3 methods; AI-assisted reading is increasingly used. Advanced bone age is characteristic of precocious puberty.^[6]
2. Basal LH and FSH in the early morning with a sensitive assay. A morning LH of roughly 0.1 IU/L or higher can support true puberty; thresholds vary (0.1 to 1.0 IU/L) and some cases are ambiguous.
3. Serum oestradiol in girls and testosterone in boys in the early morning. A low value does not exclude puberty, but a high value with low gonadotropins points to a peripheral cause.
4. GnRH stimulation test when basal results are ambiguous: 100 micrograms of gonadorelin intravenously with a single sample at 30 to 40 minutes, or 3.75 mg of leuprorelin with a sample between 30 and 180 minutes. A peak LH above 5 IU/L (some laboratories use 4 to 8 IU/L) defines active puberty; the LH to FSH ratio is less reliable.^[6]
5. Pelvic ultrasound in girls to assess ovarian and uterine size, endometrial echo and ovarian cysts.
6. Testicular ultrasound in boys when volumes are asymmetric or a mass is suspected.
7. Brain MRI when central precocious puberty is confirmed and the child is under 8 years (under 8 to 9 years for boys in recent guidance), or sooner at any age with neurological symptoms, rapid progression, or no family history of early puberty. In boys presenting between 8 and 9 years without neurological signs, routine MRI is not needed.^[3]
8. Karyotype for girls with delayed puberty and raised gonadotropins (Turner syndrome) and for boys with tall stature, small firm testes or gynaecomastia (Klinefelter syndrome).
9. Thyroid function to rule out severe hypothyroidism, which can mimic peripheral precocious puberty.
10. IGF-1 and clinical assessment of growth. Raised IGF-1 supports pubertal activation.

Basal LH sensitivity for central precocious puberty ranges from about 50 to 100% with specificity 64 to 100%.^[6]

• High LH and FSH with high sex steroids — primary (peripheral) gonadal failure in delayed puberty, or a compliant HPG axis in normal puberty.
• Low LH and FSH with high sex steroids — peripheral precocious puberty or an exogenous source.
• Low LH and FSH with low sex steroids — hypogonadotropic hypogonadism or functional delay.
• Bone age advanced with high sex steroids — precocious puberty of whatever type.
• Bone age delayed — delayed puberty or constitutional delay.
• Testis under 4 mL with pubic hair — virilisation without testicular activation.

For treatment monitoring, the numbers used in practice are well defined, although the Endocrine Society 2026 guideline advises against routine biochemical testing during GnRH-analogue therapy: peak stimulated LH should fall below 4 IU/L during effective therapy and below 3 IU/L in many cohorts. Oestradiol suppression below 20 pg/mL (73.4 pmol/L) and testosterone below 30 ng/dL (1.04 nmol/L) confirm adequate gonadal suppression, with bone age and growth velocity also expected to fall. ^{[4] [7]}

Tanner staging is the standard clinical method. It has two sex-specific scales plus pubic hair for both sexes, and it is applied from stage 1 (prepubertal) to stage 5 (adult).^[1]

Androgen (pubarche) stages are recorded separately for pubic hair, and growth is tracked on standard charts.

1. Confirm true pubertal change (thelarche in girls, testicular enlargement in boys) that is progressive and associated with growth acceleration and bone age advancement.
2. Exclude variants: premature thelarche, premature adrenarche, lipomastia, exogenous hormone exposure, obesity-related apparent breast development.
3. Classify as central or peripheral using gonadotropins, sex steroids and (when needed) GnRH testing.
4. Identify a cause: history and examination, then brain MRI for central cases at the appropriate ages, pelvic or testicular ultrasound, and karyotype or targeted genetic testing where indicated.

• Constitutional delay: delayed height for family, delayed bone age, and a family history of late bloomers; normal variant.
• Hypergonadotropism: raised LH and FSH; karyotype for Turner or Klinefelter syndrome; consider radiation or chemotherapy.
• Permanent hypogonadotropism: absent puberty with low gonadotropins and anosmia, cranial imaging, pituitary hormones.
• Functional hypogonadotropism: chronic disease, malnutrition, hypothyroidism, eating disorder or overtraining.

The aim is to postpone sexual development and skeletal maturation long enough to preserve adult height and to avoid the social and emotional burden of early puberty. Treatment should be started early in rapidly progressive disease and generally stopped when puberty can safely resume, guided by bone age.

Long-acting GnRH analogues are the standard treatment. They are given continuously rather than pulsatile, so the GnRH receptor desensitises and LH and FSH fall to prepubertal levels, sex steroids fall, growth velocity slows and bone age advancement decreases.^{[4][6] [2]}

Formulations used in practice include:

• Leuprolide (leuprorelin) acetate depot: 3.5 mg or 7.5 mg monthly (every 4 weeks) or 11.25 mg every 3 months. A 3-month dosage of 11.25 mg suppresses peak stimulated LH below 3 IU/L in about 94% of children at 6 months. ^[4]
• Triptorelin depot: monthly or 3-monthly preparations are also widely used.
• Histrelin subcutaneous implant: gives 12 months of suppression and is convenient where available. ^[6]
• Intranasal nafarelin and other preparations exist but are less used in children.

An implant is placed under the skin of the upper arm under local anaesthesia and provides about a year of suppression.^[6]

Monitoring combines clinical response (Tanner stage, growth velocity), periodic bone age radiograph, and, in many centres, basal or GnRH-stimulated LH with oestradiol or testosterone. The Endocrine Society 2026 guideline advises against routine biochemical monitoring during GnRH-analogue therapy, reserving biochemical testing for clinically suspected treatment failure. Failure is suggested by continuing breast or testicular development, rising growth velocity or advancing bone age, when the dose or interval should be adjusted. ^{[4][6] [7]}

Common adverse effects are injection pain, transient headaches, hot flushes and mild gastrointestinal symptoms. Withdrawal bleeding can occur after the first injection in girls. Side effects of 11.25 mg leuprolide at 3-month intervals are usually mild to moderate; a sterile abscess is rare but may reduce treatment efficacy and can lead to stopping treatment. Some studies report modest weight gain on treatment, so lifestyle advice matters.^[4][6]

Treatment targets the source of excess sex steroids:

• Congenital adrenal hyperplasia — suppress adrenal androgens with glucocorticoids and address salt handling where needed. ^[6]
• McCune–Albright syndrome — aromatase inhibitors (letrozole, anastrozole) to block conversion of androgens to oestrogens; bisphosphonates for bone pain; observation during fluctuating cyst activity.
• Familial male-limited puberty (testotoxicosis) — antiandrogen (spironolactone) plus an aromatase inhibitor.
• Sex steroid-secreting tumours — surgical resection is first-line. ^[6]
• Exogenous hormone exposure — stop and observe.
• Profound hypothyroidism — thyroid replacement reverses the picture.

Constitutional delay needs patience, counselling, reassurance and usually no medication, although a short 3 to 6 month course of low-dose testosterone in boys (or oestrogen in girls) can be used to start development while the axis catches up. Permanent hypogonadism is treated with puberty induction and then long-term sex hormone replacement to maintain adult bone, muscle and wellbeing. Primary gonadal failure may need specific management; Turner syndrome requires ovarian function monitoring and, later, hormone replacement therapy. Early referral to paediatric endocrinology is wise.^[1][6]

Most pubertal gynaecomastia needs reassurance and observation only. If the lump is persistent, painful, progressive, asymmetric or accompanied by testicular abnormalities, investigate. Treatment is driven by the cause: stop an offending drug, treat hypogonadism (testosterone only for proven hypogonadism), and consider surgery for long-standing fibrotic tissue or marked psychological distress. Tamoxifen or raloxifene may be used in selected persistent painful cases, and psychological support is important for adolescents.^[5]

Untreated precocious puberty leads to early epiphyseal closure and short adult height despite tall stature in childhood, along with anxiety, depression, behavioural difficulty and low self-esteem from looking older than one is. Early menarche increases lifetime oestrogen exposure and is associated with increased breast cancer risk. Delayed puberty can cause low self-esteem, social withdrawal and osteopenia if untreated. In delayed puberty, the underlying condition (brain tumour, chronic disease, eating disorder) can be missed if the delay is dismissed as constitutional. Adolescents with gynaecomastia may develop significant psychological distress and body-image disturbance.^[1][5][6]

• Constitutional delay resolves with time; adult height is usually normal for family.
• Idiopathic central precocious puberty responds well to GnRH analogues when started early, with pubertal progression halted or reversed and predicted adult height improved.
• Peripheral causes carry the prognosis of their underlying condition; tumours need early recognition.
• Pubertal gynaecomastia spontaneously regresses in most boys within months to 2 years.
• Turner and Klinefelter-related pubertal disorders have good outcomes with timely hormone replacement but require long-term follow-up.^[1][5]

Puberty cannot be prevented, but risk can be reduced and cases detected early:

• Maintain healthy weight through balanced diet, regular aerobic activity, adequate sleep and limited screen time; obesity is a major modifiable driver of earlier puberty.
• Limit exposure to endocrine-disrupting chemicals such as phthalates and bisphenol A where feasible.
• Ask about family puberty timing in routine child health visits.
• Encourage parents and schools to recognise normal Tanner stages and the age thresholds for concerning early or late puberty.
• Routine growth and pubertal assessment at child health visits, and every 3 to 6 months where puberty is uncertain, catches most cases; ambulatory paediatric practice can add bone age radiography when growth or puberty is unusual. ^[7]
• A family history of pubertal delay, maternal menarche under 10 years or paternal voice change very early provides clues.

Much of this evidence is associational rather than causal, especially for environmental exposures.^[2][3]

Pregnancy and mini-puberty. Brief physiological breast enlargement in newborns of both sexes usually resolves within weeks. This is not disease and does not need treatment.

Children with DSD. Disorders of sex development may present with atypical puberty; these require a specialised multidisciplinary team rather than a standard puberty protocol.^[1]

Obesity. Obesity favours early puberty in girls and may delay it in boys; IGF-1 and fat mass signals differ between sexes, so the clinical picture must be interpreted in context.^[2]

Survivors of childhood cancer. Cranial or gonadal radiation and chemotherapy can cause either precocious or delayed puberty. Routine endocrine surveillance after treatment detects both patterns early.

Adolescent boys with persistent distressing gynaecomastia. Surgical and psychological referral should not be delayed until late adulthood when the problem is clearly established.^[5]

• A left-hand bone age radiograph and a single sensitive LH are the highest-yield first investigations where available.
• Where GnRH is not available, a basal LH with careful clinical assessment (Growth chart, Tanner stages, testicular volume) provides a reasonable starting point.
• Leuprolide and triptorelin depots are expensive; discuss costs and treatment duration realistically with families before starting.
• Brain imaging should be reserved for young age or red flags, not applied to all boys with precocious puberty.
• Reassurance and good documentation of pubertal progression are effective tools and cost nothing.
• Refer early when there is neurological disease, a very young onset (under 6 years), rapidly progressive puberty, or suspected tumour or disorder of sex development.^[3]

Puberty and sexual development connects to hypothalamic–pituitary–adrenal and thyroid function, growth hormone disorders, disorders of sex development, growth monitoring, thyroid disease, chronic childhood disease (coeliac and inflammatory bowel disease), Turner syndrome, Klinefelter syndrome, hyperprolactinaemia, congenital adrenal hyperplasia and oncology (intracranial tumours, hCG-secreting germ cell tumours).