Hormonal changes during adolescence

The hormonal switch flips

Puberty begins when the brain decides it is time. The mechanism is complex but the result is the gradual ramping up of the hormonal system that will run through the reproductive years.

The brain decides

Puberty starts in the hypothalamus, a part of the brain. Around age 8 to 13 in girls the hypothalamus begins releasing gonadotropin releasing hormone (GnRH) in pulses. This signals the pituitary gland to produce FSH and LH, which in turn signal the ovaries to start producing oestrogen. The whole hormonal cascade switches on. The exact timing is influenced by genetics, nutrition and environmental factors.

Oestrogen takes the lead

Oestrogen is the dominant hormone of female puberty. It drives breast development, the redistribution of body fat that creates female body shape, growth in height, changes in the reproductive organs and many smaller changes. The rise in oestrogen happens gradually over years rather than suddenly. Levels are still fluctuating significantly through the early years after periods start.

The growth spurt

Girls typically have their growth spurt 1 to 2 years before boys, peaking around age 12. The growth spurt is driven by oestrogen and growth hormone. Most girls reach their adult height within 2 to 3 years of starting periods. Late developing girls catch up but may end up shorter than they would have done if puberty had started earlier. The timing is largely genetic.

What can affect timing

Early puberty (before age 8) and late puberty (no signs by age 13) both warrant medical assessment. Most timing variation is within the normal range and reflects genetics. Nutrition affects timing, with chronic undernutrition delaying puberty. Body fat percentage influences the timing of menarche specifically. Speak to your GP if you have concerns about pubertal timing.

What happens in what order

Puberty follows a broadly consistent sequence even though the exact timing varies between individuals. Knowing the typical order helps make sense of what is happening.

Breast development

Breast budding is usually the first visible sign of puberty, typically appearing around age 9 to 11. The development continues over several years through identifiable stages (the Tanner stages). Breast development is asymmetrical for many girls, with one side developing slightly before the other. This usually evens out but some asymmetry is common in adult women too.

Pubic and underarm hair

Pubic hair appears shortly after breast development starts. Underarm hair typically appears 1 to 2 years later. Hair growth is driven partly by oestrogen and partly by androgens (the testosterone family) which the adrenal glands and ovaries also produce. The amount and pattern of body hair varies significantly between girls and is largely genetic.

Periods start

Periods (menarche) typically start 2 to 3 years after breast development began. The average age in the UK is around 12 to 13. The first periods may be light, brown and irregular. The first 2 to 3 years of cycles are often very irregular as the hormonal system matures. Most cycles become more regular by age 16 to 17.

Body shape changes

Female body shape develops as fat redistributes toward hips, thighs and breasts under the influence of oestrogen. This continues for several years. The final adult shape typically settles by the late teens. Body image issues are particularly common during this period because the body is actively changing while peer comparison is intense.

The other effects of female puberty

Puberty is not just physical changes. The hormonal system affects brain, mood, sleep and behaviour in ways that have significant impact on adolescent life.

Mood and emotions

The hormonal fluctuations of puberty affect mood. Adolescents can experience much wider mood swings than they did as children. Sensitivity to social situations increases. The combination of brain changes (which are also happening) and hormonal changes creates the emotional intensity that defines teenage years. This is normal even when it is difficult.

Sleep changes

The body clock shifts later during adolescence. Teenagers naturally want to go to sleep later and wake up later. School schedules conflict with this biological pattern, contributing to widespread sleep deprivation in adolescents. The combination of hormonal changes, brain changes and sleep deprivation makes adolescence particularly demanding on mental health.

Mental health risks

Depression and anxiety rates rise significantly in girls from age 12 onward. The pattern persists through adulthood. Multiple factors contribute including hormonal changes, social pressures, body image issues and the general challenges of growing up. Recognising depression or anxiety in adolescent girls and getting help early matters. Speaking to a GP is a good starting point.

Acne and skin

The rise in androgens during puberty increases oil production in skin, leading to acne for many adolescents. Acne usually peaks in mid to late adolescence and improves over time. Treatment options ranging from over the counter products through to prescription medications can help significantly. Severe acne in adolescence can affect self esteem and warrants treatment. Speak to a GP if over the counter approaches are not enough.

Supporting adolescent female health

Adolescence is a foundational period for lifelong health. The habits and patterns established now set up the years ahead. A few key areas deserve particular attention.

Building bones

Around 90 percent of peak bone density is achieved by age 18. This is the most important period for building strong bones for life. Adequate calcium and vitamin D, weight bearing exercise and adequate energy intake all support bone development. Restrictive eating or excessive exercise during these years can affect peak bone density for life. Speaking to a GP if cycles are absent or irregular for prolonged periods matters.

Eating well enough

Adolescent girls have high nutritional needs because of growth and hormonal development. Restrictive eating, fad diets and disordered eating patterns are unfortunately common in this age group. Eating disorders are particularly common in teenage girls and have significant long term effects. Parents, schools and healthcare professionals should watch for warning signs.

Mental health support

Depression and anxiety in adolescent girls are common and treatable. Schools, GPs and child and adolescent mental health services (CAMHS) all have roles. Long waiting times for CAMHS in many areas are a real problem. Earlier intervention produces better outcomes. Talking openly about mental health helps reduce the stigma that prevents young people from seeking help.

Knowing what is normal

Many adolescent girls have questions about their bodies that they feel unable to ask. Reliable information helps. NHS resources, books written for young people and conversations with trusted adults all provide context. Schools provide some education but quality varies. Encouraging questions and providing accurate answers supports better health outcomes than leaving young people to figure things out alone.

More on female health

For the menstrual side our Early Menstrual Health: A Guide for Young Women covers the first years of periods. How Female Health Changes From Puberty to Old Age covers the lifespan view. And The Key Hormones That Drive Female Health covers the hormones taking centre stage.