Key takeaways

  • Hormones are chemical messengers made by endocrine glands; they travel in the blood and only affect cells that carry the matching receptor.
  • Hormone levels are controlled by feedback loops, with the hypothalamus and pituitary in the brain acting as the master coordinators.
  • Puberty begins when the brain restarts GnRH release, switching on the ovaries or testes to make sex hormones.
  • The menstrual cycle is a precise back-and-forth between brain, ovaries and uterus, driven mainly by oestrogen and progesterone.
  • Thyroid disorders, PCOS and insulin resistance are common in Indian teens, often start in adolescence, and are very treatable when caught early.
  • Because one hormone affects many tissues, imbalances cause scattered symptoms across the body, which is why a simple blood test often explains a lot.

What hormones actually are

A hormone is a chemical made by a gland in one part of the body that travels through the bloodstream and produces specific effects somewhere else. The word comes from the Greek hormaein, "to set in motion," coined in 1905 by the British physiologist Ernest Starling. More than fifty hormones have been identified, and new ones are still being discovered.

The glands that make hormones are called endocrine glands, and together they form the endocrine system. "Endocrine" means secreted into the blood, unlike exocrine glands (sweat or salivary glands) that empty into ducts. The endocrine system is one of the body's two great communication networks. The nervous system sends fast electrical signals between connected cells; the endocrine system sends slower chemical signals that can reach any tissue carrying the right receptor.

A few core principles explain how hormones work:

  • Receptors create specificity. A hormone only affects cells that have its matching receptor, a protein on or inside the cell. This is why a hormone can reach every tissue through the blood but act on only a few.
  • Feedback keeps levels steady. The body monitors hormone levels and adjusts production up or down. Most loops are negative: when a level rises too high, production falls. A few are positive (high levels trigger more) but these are rare and self-limiting.
  • Hormones work in networks. The hypothalamus signals the pituitary, which signals other glands, allowing the body to coordinate complex responses across many systems at once.

The biological point of hormones is coordination across distance. Bone growth, blood-sugar control and the menstrual cycle all involve cells spread throughout the body that nerves alone could never reach. The practical point for your own health: because a single hormone touches many tissues, an imbalance often shows up as scattered, confusing symptoms (a thyroid problem can cause fatigue, weight change, mood change and hair loss at once), and treating the hormone often improves all of them together.

The main endocrine glands and what they do

  • Hypothalamus — a small region at the base of the brain that links the nervous and endocrine systems. It releases signalling hormones (GnRH for puberty and periods, TRH for the thyroid, CRH for stress, GHRH for growth) that act on the pituitary, and makes oxytocin and vasopressin. It is the conductor of the endocrine orchestra.
  • Pituitary gland — a pea-sized "master gland" below the hypothalamus. It releases FSH and LH (ovaries and testes), TSH (thyroid), ACTH (adrenals), growth hormone and prolactin.
  • Thyroid gland — a butterfly-shaped gland in the front of the neck. It makes thyroxine (T4) and triiodothyronine (T3), which set the body's metabolic rate. It needs adequate iodine to work.
  • Parathyroid glands — four tiny glands behind the thyroid that release parathyroid hormone (PTH) to regulate blood calcium.
  • Adrenal glands — sit on top of the kidneys. The cortex makes cortisol (the main stress hormone), aldosterone (salt and water balance) and some androgens; the medulla makes adrenaline and noradrenaline for the fight-or-flight response.
  • Pancreas — behind the stomach. Its endocrine cells make insulin (lowers blood sugar) and glucagon (raises it).
  • Ovaries — make oestrogen, progesterone and small amounts of androgens, driving female puberty, the menstrual cycle, fertility and pregnancy. Production declines around menopause.
  • Testes — make testosterone and a little oestrogen, driving male puberty, sperm production and muscle and bone development.
  • Pineal gland — a small gland in the brain that releases melatonin to regulate the sleep–wake cycle.
  • Thymus — most active in childhood; mainly an immune organ that helps develop T-cells.

The three chemical families of hormones

Hormones are grouped by chemical structure, which decides how they are made, how they travel and how fast they act.

Peptide and protein hormones are chains of amino acids — insulin, growth hormone, oxytocin, FSH, LH, TSH and many more. They are water-soluble, so they bind receptors on the cell surface and trigger fast signals inside. They act in seconds to minutes but break down quickly. Because digestion destroys them, peptide hormones such as insulin usually have to be injected rather than swallowed.

Steroid hormones are made from cholesterol and share a four-ring structure — the sex hormones (oestrogen, progesterone, testosterone), the adrenal corticosteroids (cortisol, aldosterone) and vitamin D. They are fat-soluble, cross the cell membrane easily and act on receptors inside the cell, usually by switching genes on or off. They act more slowly (minutes to hours) but last longer, and they can be taken as tablets — which is why birth control pills are steroid hormones.

Amine hormones are built from single amino acids — adrenaline and noradrenaline (fast, surface-acting), thyroid hormones (slow, gene-acting) and melatonin.

This explains a lot of everyday medicine: levothyroxine for an underactive thyroid is an amine taken as a daily tablet, the combined contraceptive pill uses steroid hormones, and insulin for diabetes is a peptide that must be injected. Each medicine works through the mechanism of its hormone family.

How hormones drive puberty

The usual sequence in girls

In girls, breast budding (thelarche) is usually the first sign, around age 10–11 (normal range 8–13), followed over 2–4 years by the later Tanner stages of breast growth. Pubic hair, then underarm hair, appear along the way. The growth spurt peaks mid-puberty (around breast stage 3), with Indian girls averaging 8–10 cm a year at peak. The first period (menarche) comes later, usually about 2–2.5 years after breast budding, at an average age of 12–13. Most girls grow only a few more centimetres after menarche.

The usual sequence in boys

In boys the first sign is usually testicular enlargement around age 11–12, followed by pubic hair. The growth spurt comes later than in girls (around Tanner stage 4), averaging 9–11 cm a year at peak, with voice deepening, facial and body hair, and increased muscle developing through puberty.

When timing is too early or too late

Timing varies widely and runs in families. Signs before age 8 in girls (or 9 in boys) suggest precocious puberty and deserve evaluation, while no signs by age 13 in girls (or 14 in boys) suggest delayed puberty. Nutrition and body composition both influence timing, which is why the average age of menarche has fallen over the past century. Alongside the hormones, the brain is rewiring — the prefrontal cortex (planning and impulse control) keeps developing into the early twenties — which is part of why this stage can feel like an emotional rollercoaster. Many widespread puberty myths come from not understanding these timelines.

The menstrual cycle, hormone by hormone

The menstrual cycle is one of the body's most precisely coordinated hormonal sequences. A typical cycle is about 28 days but anywhere from 21 to 35 days is normal in adults; cycles are often irregular for the first 2–3 years after menarche while the system matures.

Day 1 is the first day of bleeding.

Follicular phase (day 1 to ovulation): FSH prompts the ovaries to grow several follicles, each holding an egg. One becomes dominant and pumps out rising oestrogen, which thickens the uterine lining.

Ovulation (around day 14 in a 28-day cycle): high oestrogen triggers a surge of LH (one of the body's rare positive feedback loops), and about 36 hours later the egg is released. The egg survives about 24 hours; sperm can survive about 5 days, so the fertile window spans several days. Some people feel a twinge mid-cycle, called ovulation pain or Mittelschmerz.

Luteal phase (ovulation to next period): the empty follicle becomes the corpus luteum and makes progesterone, which holds the lining in place. If there is no pregnancy, it breaks down after 10–14 days, progesterone falls, and the lining sheds — the next period. If pregnancy occurs, the embryo makes hCG to keep progesterone going.

Understanding what ovulation actually means and tracking these phases helps make sense of energy, skin and mood shifts across the month. Patterns that are well outside the normal range — cycles under 21 or over 45 days, absent periods after the first 2–3 years, period pain that interferes with daily life, or very heavy bleeding — deserve a gynaecologist's review, as they can point to PCOS, thyroid problems or other treatable conditions.

Thyroid hormones and why thyroid disease is common in India

  • Hypothyroidism (underactive): the most common form. Fatigue, weight gain, cold intolerance, dry skin and hair, constipation, low mood, irregular or heavy periods. The usual cause is Hashimoto's, an autoimmune condition. Treatment with levothyroxine (Eltroxin, Thyronorm) is simple, effective and cheap.
  • Hyperthyroidism (overactive): less common. Weight loss despite a good appetite, heat intolerance, tremor, racing heart, anxiety and poor sleep. Often caused by Graves' disease.
  • Goitre and nodules: an enlarged thyroid or lumps; most nodules are benign but need evaluation by ultrasound and sometimes a biopsy.
  • Thyroid cancer: relatively uncommon and usually has a good outlook with treatment.

PCOS in Indian adolescents

  • Irregular cycles (often longer than 35–45 days, sometimes missed for months)
  • Persistent acne that does not respond to usual treatments
  • Excess hair on the face, chest or abdomen (hirsutism)
  • Weight gain or difficulty losing weight, oily skin, scalp hair thinning
  • Dark velvety patches on the neck or armpits (acanthosis nigricans, a sign of insulin resistance)

Insulin, blood sugar and the rise of diabetes in Indian teens

Prevention starts young

Lifestyle is the foundation: cutting sugary drinks and refined carbohydrates, at least 60 minutes of activity a day for adolescents, 8–10 hours of sleep (which supports insulin sensitivity), and weight management where needed. For pre-diabetes, lifestyle change alone often reverses the trend; for type 2 diabetes in teens, lifestyle plus metformin is usual. For an India-focused overview, see type 2 diabetes in Indian women.

Stress hormones, mood and mental health

Help is available in India

Mental health support for adolescents has grown through NIMHANS, the Indian Psychiatric Society and the Rashtriya Kishor Swasthya Karyakram clinics. Free, confidential helplines include iCall (9152987821), Vandrevala (1860-2662-345), AASRA (9820466726) and Sneha (044-24640050). The Mental Healthcare Act 2017 supports the right to access care.

Common hormone myths, and the actual science

Myth: hormones are strictly 'male' or 'female'

Fact: the sex hormones are present in everyone. People with ovaries make both oestrogen and testosterone; people with testes make both too. The ratios differ between typical male and female physiology, but both hormones are essential in everyone for bone, brain and heart health. Calling testosterone "the male hormone" is a simplification — balance and amount matter far more than presence or absence.

Myth: hormonal contraception causes infertility later

Fact: it does not. Fertility returns to baseline after stopping. Combined pills usually see cycles return within 1–3 months; the hormonal IUD reverses quickly on removal; the contraceptive injection (DMPA) can take longer, sometimes 6–12 months, but full fertility does return. The idea that the pill "depletes" or "damages" the system is not supported by evidence.

Myth: PCOS means you cannot have children

Fact: most people with PCOS can have children, often without specialised fertility treatment. PCOS can disrupt ovulation, but lifestyle measures and ovulation-inducing medicines (such as letrozole) work well, and India's reproductive medicine infrastructure is well developed. A PCOS diagnosis is not a catastrophe — it is a manageable condition.

Myth: thyroid medication is a lifelong trap to avoid

Fact: for most hypothyroidism, levothyroxine is indeed usually lifelong, but it is nearly identical to the body's own T4, well tolerated and very cheap (about ₹30–100 a month). The real harm comes from not treating an underactive thyroid, which damages energy, mood, heart health, fertility and pregnancy. Avoiding a safe daily tablet is the worse trade-off.

When to see a doctor

  • No signs of puberty by age 13 in girls or 14 in boys, or puberty starting before age 8 in girls or 9 in boys
  • Periods that are still very irregular more than 2–3 years after the first one, or that stop for several months
  • Very heavy bleeding (soaking a pad every 1–2 hours, large clots, or bleeding longer than 7 days) or period pain that stops you doing daily activities
  • Persistent unexplained fatigue, weight change, cold or heat intolerance, hair loss or a neck swelling — possible thyroid signs
  • Frequent urination, intense thirst and unexplained weight loss — possible diabetes that needs urgent assessment
  • Acne, excess facial or body hair or dark skin patches together with irregular cycles — possible PCOS
  • Severe low mood, anxiety or distress, especially if it appears in a clear cyclical pattern before periods

Frequently asked questions

What are hormones in simple words?

Hormones are chemical messengers made by glands. They travel through the blood and tell different parts of the body what to do — such as growing, starting puberty, managing blood sugar, running the menstrual cycle, and responding to stress. A hormone only affects cells that carry the matching receptor.

How many types of hormones are there?

There are more than fifty hormones, grouped into three chemical families: peptide hormones (like insulin and growth hormone), steroid hormones (like oestrogen, progesterone and testosterone) and amine hormones (like adrenaline, thyroid hormones and melatonin). The family decides how a hormone is made, how it travels and how fast it acts.

Which hormones control puberty and periods?

Puberty starts when the hypothalamus releases GnRH, prompting the pituitary to release FSH and LH, which switch on the ovaries or testes to make sex hormones. The menstrual cycle is then run mainly by oestrogen (which builds the uterine lining) and progesterone (which maintains it), with an LH surge triggering ovulation.

What is a hormonal imbalance and how do I know if I have one?

A hormonal imbalance means too much or too little of a hormone. Because hormones affect many tissues, symptoms are often scattered — irregular periods, fatigue, weight or mood changes, acne, excess hair or hair loss. Simple, affordable blood tests (TSH for thyroid, fasting sugar and HbA1c for insulin, androgens for PCOS) usually clarify what is going on.

Are thyroid problems and PCOS really that common in Indian teens?

Yes. India has one of the highest rates of thyroid disease globally, and PCOS affects roughly 5–15% of Indian women of reproductive age, often appearing in adolescence. Indian teens also carry higher metabolic risk for insulin resistance. The good news is that all three are very treatable when caught early.

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