What your thyroid does

Your thyroid is a small, butterfly-shaped gland in your neck that makes hormones to control how fast your body uses energy. Think of it like a thermostat for your metabolism — the chemical processes that keep you alive. When your thyroid works properly, it releases the right amount of hormone to keep your heart rate, body temperature, and digestion at a steady pace. When it makes too much or too little hormone, nearly every system in your body feels the difference.

The thyroid sits just below your Adam's apple, wrapped around your windpipe. You usually cannot feel it unless something is wrong. It weighs about as much as a dime, but it touches almost every cell in your body through the hormones it releases into your bloodstream.

Key Takeaways

  • Your thyroid makes hormones that control how fast your body burns energy, affecting your heart rate, temperature, digestion, and mood.
  • The pituitary gland in your brain tells your thyroid when to make more or less hormone, creating a feedback loop that keeps levels balanced.
  • When your thyroid makes too much hormone (hyperthyroidism), you may feel anxious, lose weight, and sweat more than usual.
  • When your thyroid makes too little hormone (hypothyroidism), you may feel tired, gain weight, and feel cold more easily.
  • A simple blood test can measure your thyroid hormone levels and help doctors figure out if your thyroid is working properly.

How your thyroid makes and releases hormones

Your thyroid produces two main hormones: T4 and T3. T4 is the inactive form — your body stores it and converts it to T3 when cells need energy. T3 is the active form that actually tells your cells to speed up or slow down. Your thyroid also makes a hormone called calcitonin, which helps control calcium levels in your blood.

The thyroid does not decide on its own how much hormone to make. Your pituitary gland, a pea-sized gland at the base of your brain, sends a signal called TSH (thyroid-stimulating hormone) that tells your thyroid to produce more or less. When thyroid hormone levels drop, the pituitary releases more TSH. When levels rise, the pituitary releases less. This back-and-forth keeps your thyroid in balance — doctors call it a feedback loop.

What happens when your thyroid makes too much hormone

When your thyroid produces excess hormone, the condition is called hyperthyroidism. Your metabolism speeds up, and your body burns energy faster than normal. Common symptoms include a racing heartbeat, anxiety, trembling hands, weight loss even when eating normally, excessive sweating, and trouble sleeping. You may also feel irritable or have trouble concentrating. Some people develop a swollen thyroid (called a goiter) or notice their eyes feel puffy or bulging.

Hyperthyroidism can come from several causes. Graves' disease, an autoimmune condition where your immune system attacks your thyroid, is the most common. Thyroiditis (inflammation of the thyroid) and thyroid nodules that produce extra hormone can also cause it. Certain medications and too much iodine can trigger it as well.

What happens when your thyroid makes too little hormone

When your thyroid produces too little hormone, the condition is called hypothyroidism. Your metabolism slows down, and your body burns energy more slowly. Common symptoms include fatigue, weight gain even when eating less, feeling cold more easily, dry skin and hair, constipation, and depression or mood changes. You may also notice your voice sounds hoarse or your face looks puffy.

Hashimoto's disease, an autoimmune condition where your immune system attacks your thyroid tissue, is the most common cause of hypothyroidism. Other causes include iodine deficiency, thyroid surgery or radiation, certain medications, and pregnancy-related thyroid problems. Hypothyroidism develops slowly, so you might not notice symptoms for months.

How doctors test your thyroid

A doctor can check your thyroid with a simple blood test that measures TSH and thyroid hormones. The most common test measures TSH first — if that level is abnormal, the doctor usually orders a second test to measure T4 or T3. These tests tell your doctor whether your thyroid is working properly or if it is making too much or too little hormone.

Your doctor may also feel your neck to check if your thyroid is enlarged or has lumps. An ultrasound can show the size and shape of your thyroid and spot nodules. If your doctor finds a nodule, they may order additional imaging or a biopsy to rule out cancer, though most thyroid nodules are not cancerous.

Why your thyroid matters for your overall health

Because thyroid hormone affects nearly every cell in your body, thyroid problems can influence your weight, mood, energy, heart health, and bone strength. Untreated hyperthyroidism can lead to heart problems and bone loss. Untreated hypothyroidism can raise cholesterol and increase the risk of heart disease. Thyroid problems during pregnancy can affect the baby's brain development.

The good news is that both hyperthyroidism and hypothyroidism are treatable. Hypothyroidism is usually managed with a daily thyroid hormone pill that replaces what your body is not making. Hyperthyroidism can be treated with medication, radioactive iodine, or surgery, depending on the cause. Once treated, most people feel much better and can live a normal life.

When to see a doctor about your thyroid

See your doctor if you notice unexplained weight gain or loss, persistent fatigue, changes in your heart rate, mood changes, or trouble tolerating heat or cold. If you have a family history of thyroid disease, your doctor may recommend screening even if you have no symptoms. Women over 60 and anyone with other autoimmune conditions should discuss thyroid screening with their doctor.

If you already know you have a thyroid condition, regular blood tests help your doctor make sure your treatment is working. Most people on thyroid medication need their levels checked once or twice a year, though some need more frequent testing when starting or changing treatment.

Frequently Asked Questions

Can you feel your thyroid if it is normal?

No. A normal thyroid is small and soft, tucked under your neck muscles where you cannot feel it. If you can feel a lump or swelling in your neck, that usually means something is wrong — either the thyroid is enlarged, has nodules, or is inflamed. Tell your doctor if you notice any swelling or lumps in your neck.

Does thyroid disease run in families?

Yes. Both Hashimoto's disease and Graves' disease tend to run in families, especially on the mother's side. If your parent or sibling has thyroid disease, your risk is higher. This does not mean you will definitely develop it, but it means you should mention your family history to your doctor and watch for symptoms.

Can stress cause thyroid problems?

Stress does not cause thyroid disease, but it can make symptoms worse if you already have it. Stress can also trigger thyroiditis (inflammation of the thyroid) in people who are already at risk. Managing stress through sleep, exercise, and relaxation may help you feel better if you have a thyroid condition.

What is the difference between TSH and thyroid hormone?

TSH is a signal from your pituitary gland that tells your thyroid to make more or less hormone. Thyroid hormone (T4 and T3) is what your thyroid actually produces. Doctors measure both because they work together — high TSH usually means your thyroid is not making enough hormone, while low TSH usually means it is making too much.

Can you live without a thyroid?

Yes, but you will need to take thyroid hormone medication for the rest of your life. Some people have their thyroid removed because of cancer, nodules, or severe hyperthyroidism. Once removed, your body cannot make thyroid hormone on its own, so you take a daily pill to replace it. With proper medication, people without a thyroid live normal, healthy lives.