Being two years behind your friends in physical development, in the years when peer comparison is at its most brutal, is genuinely hard. Most teenagers who are late to start puberty are completely normal — their body is just running on a slower clock, and they will catch up — but that medical reassurance doesn't always reach the changing room. The job of a good doctor here is twofold: rule out the small number of cases with an underlying cause, and take the social and psychological impact seriously even when the medical picture is reassuring. For more on growth and adolescent health, visit Healthbooq.
When Puberty Counts as Delayed
The clinical thresholds are set roughly two standard deviations later than the population average:
- Girls: no breast development (thelarche) by age 13
- Boys: testicular volume under 4 ml (Tanner stage 1) by age 14
In girls, primary amenorrhoea — no periods by age 15 despite some pubertal development, or no periods within 5 years of breast development starting — is also a reason for assessment.
These thresholds are population-based and have not been revised in the last few decades, even though the average age of puberty onset has shifted somewhat earlier in many populations (a trend documented across multiple international cohorts). What that means in practice: the upper end of "normal late" is genuinely at the edges, and a teenager who hits these thresholds deserves an actual workup, not a "give it more time" brush-off.
What's Most Likely Going On
The causes split into three groups, with very different implications.
Constitutional delay of growth and puberty (CDGP) is by far the most common — around 60 per cent of cases in boys, somewhat less in girls. CDGP is a normal variant: the hypothalamic-pituitary-gonadal axis switches on later than average, but everything works correctly when it does. Adult height, fertility, and bone density are all normal.
The clues that point to CDGP: a family history of late puberty (a father who didn't shave until university; a mother whose first period was at 15 or 16), a child who has always been short for age but tracking on their own growth curve, and a bone age X-ray that shows the skeleton is younger than the chronological age — meaning there's still growth potential ahead.
Functional hypogonadism is the body deliberately switching off the puberty axis because something else is wrong. The single most common cause is low body weight — undereating, anorexia or other eating disorders, or very high training loads in athletic teenagers. The female athlete triad (low energy availability, menstrual dysfunction, low bone density) is well-recognised in gymnasts, distance runners, and dancers.
Other causes in this group include coeliac disease (sometimes the only sign is a stalled growth curve), inflammatory bowel disease, chronic kidney disease, untreated hypothyroidism, hyperprolactinaemia, and any chronic illness that's draining energy. Treat the underlying cause and puberty usually resumes.
True hypogonadism is the smallest group but the one not to miss. Primary hypogonadism means the gonads themselves aren't working — most commonly Turner syndrome in girls (45,X, often accompanied by short stature, webbed neck, cardiac findings) and Klinefelter syndrome in boys (47,XXY, often presenting with tall stature and delayed/incomplete puberty). Chemotherapy or radiation history is another cause.
Secondary (central) hypogonadism is failure at the hypothalamus or pituitary — Kallmann syndrome (gonadotropin deficiency plus an absent or reduced sense of smell), other congenital pituitary problems, panhypopituitarism, or tumours. The anosmia question — "can you smell your breakfast in the morning?" — is genuinely useful clinically.
What an Assessment Looks Like
A teenager presenting with delayed puberty needs a proper history and examination — not a quick "wait and see." Things the doctor should cover:
- Detailed growth history with the centile chart
- Family history of pubertal timing (parents and siblings)
- Nutrition and any restriction patterns; exercise volume
- Chronic symptoms: bowel changes, fatigue, weight loss, headaches
- Sense of smell
- Tanner staging on examination
- Height, weight, BMI, arm span
Investigations typically include LH, FSH, oestradiol or testosterone, TSH, prolactin, full blood count, inflammatory markers, coeliac antibodies (anti-TTG IgA with total IgA), and a bone age X-ray of the left wrist. Karyotyping is added when Turner or Klinefelter is on the differential. MRI of the pituitary and hypothalamus is needed when central causes are suspected — particularly with low gonadotropins and any neurological features.
How It's Managed
CDGP: the default approach is reassurance and 6-monthly monitoring with growth measurements and Tanner staging. Most boys with CDGP will start visible puberty within 12–18 months of presenting.
For boys around 14 or older with CDGP and significant social or psychological distress, a short course of low-dose testosterone (typically 3–6 months of intramuscular or transdermal testosterone) can kickstart pubertal development. Done correctly, this doesn't compromise final adult height — the initial worry that testosterone "fuses the growth plates early" doesn't bear out at the doses used. Paediatric endocrinology should be the ones writing the script and following the response.
For girls with CDGP, low-dose oestrogen induction is sometimes used but is less commonly needed.
Hypogonadism requiring replacement is a long-term endocrinology relationship. Sex steroid replacement is started low and titrated up gradually to mimic the natural progression of puberty — testosterone in boys, oestrogen first then oestrogen plus progesterone in girls. The goal is normal pubertal development and bone health, with attention to fertility planning later.
Functional hypogonadism: treat the underlying problem. A child whose puberty has stalled because of an eating disorder needs the eating disorder treated; a child with newly diagnosed coeliac disease usually catches up on a gluten-free diet; a competitive athlete may need to reduce training load and increase calories. Hormonal treatment without addressing the cause doesn't fix the underlying problem and often misses important diagnoses.
The Psychological Side Is Not a Footnote
Being significantly behind peers in pubertal development — especially for boys, where the size difference is most visible — is associated in pediatric endocrinology research with lower self-esteem, higher rates of teasing and bullying, and increased anxiety and depression. This is real and worth taking seriously, even when the medical picture is "you're fine, just late."
In practice, the threshold for offering low-dose induction therapy in CDGP is not purely biological — it factors in how much the delay is affecting the young person's mental health, school engagement, and relationships. A 14-year-old boy who is thriving despite being prepubertal can wait. A 14-year-old who is being bullied, has stopped going to PE, and is showing signs of depression has a clear case for short-course induction even though his body would eventually do it on its own.
Talking with the young person directly — not just to the parent — about how they're experiencing this matters. So does asking about screen time around peer comparison, locker-room avoidance, and changes in social engagement.
When to See a Doctor
Book an appointment if:
- A girl has had no breast development by age 13
- A boy has had no testicular enlargement by age 14
- A girl has not started periods by age 15, or 5 years after first breast development
- A child of any age has stalled on the growth curve
- There are systemic symptoms: fatigue, gut symptoms, weight loss, headaches, vision changes
- The child is significantly distressed, regardless of strict thresholds
Most cases land on "constitutional delay, monitor and reassure," but the workup is what makes that conclusion safe rather than a guess.
Key Takeaways
Puberty is considered delayed when there is no breast development by age 13 in girls or testicular volume under 4 ml by age 14 in boys. Around 60 per cent of cases in boys are constitutional delay — late but completely normal puberty, with normal adult height and fertility. Other causes include nutritional issues, chronic illness like coeliac disease or IBD, and less commonly hormonal disorders. Most children need reassurance, careful monitoring, and sometimes a short course of low-dose sex steroids. The psychological impact is real and worth taking seriously.
