Hormones in puberty

Puberty is the multi-year transition from a child's body to one capable of reproduction, and it is driven almost entirely by hormones. A quiet hormonal system gradually switches back on, setting off a predictable but highly individual cascade of physical and emotional change.

What starts puberty

Long before any visible change, the brain sets the pace. A small region called the hypothalamus begins releasing gonadotropin-releasing hormone (GnRH) in pulses. These pulses signal the pituitary gland to release two hormones into the bloodstream: luteinizing hormone (LH) and follicle-stimulating hormone (FSH). LH and FSH in turn act on the ovaries or testes, prompting them to mature and to produce the sex hormones that reshape the body.

This pathway — hypothalamus to pituitary to gonads — is often called the HPG axis. It is active in infancy, goes largely dormant through childhood, and reawakens to begin puberty. Exactly why it reawakens when it does is influenced by genetics, body weight, nutrition, general health, and other factors that researchers are still working to fully understand. One consistent feature is that the earliest GnRH pulses tend to occur during sleep, which is part of why the first hormonal stirrings of puberty are usually invisible from the outside for some time before any physical change appears.

The characteristic hormonal changes of this stage

The defining hormonal event of puberty is the reactivation and steady strengthening of the HPG axis. Early on, the pulses of GnRH — and therefore of LH and FSH — are small and mostly nighttime events. Over months and years they grow larger and extend across the full day, so the gonads are stimulated more continuously. This is why pubertal change is progressive rather than sudden: the hormonal signal itself is ramping up gradually.

A second characteristic change is the maturing of feedback loops. In a mature reproductive system, sex hormones feed back on the brain and pituitary to keep output within a working range. During puberty these loops are still being calibrated, which contributes to the variability seen in early development and, in people with ovaries, to the irregular cycles that commonly follow the first period.

The main hormones involved

In people with ovaries, FSH and LH stimulate the ovaries to make estrogen, chiefly estradiol. Estrogen drives breast development, growth of the uterus, changes in body fat distribution, and eventually the first menstrual period. In people with testes, LH stimulates the testes to make testosterone, which deepens the voice, increases muscle and bone mass, drives growth of the penis and testes, and prompts facial and body hair.

Both groups also experience a rise in adrenal androgens — hormones from the adrenal glands — in a separate, slightly earlier process called adrenarche. Adrenal androgens contribute to underarm and pubic hair, body odor, and acne in everyone. Growth hormone and thyroid hormone work alongside the sex hormones to fuel the rapid height increase known as the growth spurt.

These hormones do not act in isolation. The growth spurt, for instance, depends on growth hormone and IGF-1 working together with the sex hormones, which is one reason the timing and the height gain track so closely with the other signs of puberty. The same sex hormones that drive visible change also signal the growth plates in the long bones to eventually close, which is what brings the growth spurt — and adult height — to a natural end.

What is typically experienced

The order of changes is more consistent than the timing. In people assigned female at birth, the first sign is usually breast budding, followed by pubic hair, a growth spurt, and then the first menstrual period (menarche). Early periods are often irregular for months to a couple of years while the hormonal feedback loops mature.

In people assigned male at birth, the first sign is usually enlargement of the testes, followed by penis growth, pubic and body hair, a growth spurt that tends to come later than in females, voice deepening, and increases in muscle mass. Temporary breast tissue (gynecomastia) is common in mid-puberty and usually resolves on its own.

Across the board, puberty commonly brings acne, body odor, mood swings, stronger emotions, changing sleep patterns, and growing interest in independence and relationships. These are expected accompaniments of a shifting hormonal landscape, not signs that something is wrong.

Common experiences and how they connect to hormones

Many of the experiences families notice during puberty trace directly back to the hormones described above. The shift toward later sleep and later waking is partly biological, reflecting changes in the body's daily rhythms during adolescence. Acne and oilier skin follow the rise in androgens. Stronger emotions and more changeable moods accompany the broader hormonal reorganization of this period, and they generally settle as the system matures. Recognizing these as expected accompaniments — rather than problems to be fixed — can take pressure off both adolescents and the adults around them.

Related tests a clinician might use

When an evaluation is warranted, a clinician usually starts with a physical examination and a careful review of growth over time, often plotted on a growth chart. The pattern of growth and development frequently provides more information than any single laboratory value.

Where blood tests are used, they may include the gonadotropins LH and FSH, which reflect the brain's signal to the gonads, and the sex hormones estradiol or testosterone, which reflect the gonads' response. In some situations a clinician may also consider thyroid tests or imaging, such as an X-ray to estimate bone age, or a scan of the brain or pelvis. The purpose of testing is to confirm the hormonal system is maturing as expected and to identify the less common situations that benefit from follow-up — not to assign a number to normal development.

When to consider talking to a clinician

Most variation in pubertal timing is healthy. A clinician can help when development seems to start unusually early, has not begun by the later end of the expected window, stalls partway, or progresses in an unexpected order. Other reasons to seek advice include periods that are extremely heavy, painful enough to disrupt daily life, or that stop after starting, as well as rapid changes that cause significant distress.

Evaluation may involve a physical exam, a review of growth over time, and sometimes blood tests of hormones such as LH, FSH, estradiol, or testosterone, or imaging. The aim is usually reassurance; testing confirms that the hormonal system is maturing as expected, and identifies the less common situations that benefit from follow-up. Bringing along a record of heights over time, and noting roughly when changes began, can make these conversations more productive.

Related reading

Explore other life-stage guides, learn more about individual hormones, or read about the blood tests used to measure them. The glossary defines terms like HPG axis and gonadotropin.