The thyroid is a small gland in your neck that controls how fast your body uses energy

Your thyroid sits at the base of your neck, just below your Adam's apple. It is shaped like a butterfly and about the size of a walnut. The thyroid makes hormones — chemical messengers — that tell your body how quickly to burn calories, how fast your heart should beat, how warm you should feel, and how fast your digestion should work. When your thyroid works right, you do not think about it. When it does not, nearly everything feels off.

The thyroid is part of your endocrine system, which is the network of glands that release hormones into your bloodstream. Those hormones travel throughout your body and control basic functions like metabolism, growth, mood, and temperature. Your thyroid produces two main hormones: T4 and T3. Both contain iodine, which is why you need iodine in your diet — your body cannot make these hormones without it.

Key Takeaways

  • Your thyroid produces hormones that control how fast your body burns energy, your heart rate, body temperature, and digestion.
  • The pituitary gland in your brain sends signals to your thyroid telling it how much hormone to make, creating a feedback loop that keeps levels balanced.
  • When your thyroid makes too much hormone, you feel jittery and lose weight; when it makes too little, you feel tired and gain weight.
  • A simple blood test can measure thyroid hormone levels and show whether your thyroid is working as it should.

How your thyroid gets the signal to make hormones

Your pituitary gland, a pea-sized gland at the base of your brain, acts as the control center for your thyroid. When your body needs more thyroid hormone, the pituitary releases a hormone called TSH (thyroid-stimulating hormone). TSH travels through your bloodstream and tells your thyroid to make and release more T4 and T3. When hormone levels get high enough, the pituitary senses this and backs off — it stops releasing as much TSH. This back-and-forth is called a feedback loop, and it keeps your thyroid hormone levels in a narrow, stable range.

Your hypothalamus, another part of your brain, sits above the pituitary and sends signals to it. So the chain goes: hypothalamus → pituitary → thyroid. If you are stressed, cold, or sick, your hypothalamus can tell your pituitary to push the thyroid harder. This is why stress and illness can affect how you feel — your thyroid responds to what your body is going through.

What happens when thyroid hormone levels are too high

When your thyroid makes too much hormone, the condition is called hyperthyroidism. Your metabolism speeds up, and your body burns energy faster than normal. People with high thyroid hormone often feel jittery, anxious, or restless. Their heart races even at rest. They sweat more, feel hot when others feel cold, and lose weight even though they are eating normally. Some people have trouble sleeping or feel their hands shaking. Their eyes may feel dry or bulge slightly. Digestion speeds up too, which can cause loose stools or diarrhea.

Hyperthyroidism can come from several causes. Graves' disease is an autoimmune condition where your immune system attacks your thyroid and makes it overactive. Thyroiditis is inflammation of the thyroid, often from a viral infection, which can cause a temporary surge of hormone. Thyroid nodules — lumps in the thyroid — can sometimes produce extra hormone on their own. Taking too much thyroid replacement medication can also cause high levels.

What happens when thyroid hormone levels are too low

When your thyroid makes too little hormone, the condition is called hypothyroidism. Your metabolism slows down. People with low thyroid hormone often feel tired no matter how much they sleep. They gain weight even though they are not eating more. Their skin becomes dry, their hair becomes brittle, and they feel cold when others feel comfortable. Digestion slows, which can cause constipation. Some people feel depressed, have trouble concentrating, or develop brain fog. Their voice may become hoarse, and their face may puff up slightly.

Hypothyroidism is most often caused by Hashimoto's disease, an autoimmune condition where your immune system attacks your thyroid and damages it over time. It can also result from iodine deficiency — if you do not get enough iodine in your diet, your thyroid cannot make enough hormone. Thyroid surgery or radiation to the neck can damage the thyroid. Some medications, like lithium or certain heart drugs, can interfere with thyroid function. Pregnancy can trigger thyroid problems in some women.

How doctors test whether your thyroid is working

A doctor checks your thyroid function with a blood test. The most common test measures TSH — the signal from your pituitary to your thyroid. If TSH is high, it usually means your thyroid is not making enough hormone, so your pituitary is pushing harder. If TSH is low, it usually means your thyroid is making too much hormone, so your pituitary has backed off. Doctors often also measure T4 and T3 directly to see how much hormone is actually in your blood.

A doctor may also feel your neck to see if your thyroid is enlarged or has lumps. An ultrasound can show the size and shape of your thyroid and whether there are nodules. If a nodule is found, a biopsy — taking a tiny sample with a needle — may be done to check whether it is cancer, though most thyroid nodules are not cancerous. These tests are straightforward and can be done in an office or outpatient clinic.

Why your age and sex matter for thyroid health

Thyroid problems are more common in women than in men, especially after age 50. Women are more likely to develop Hashimoto's disease and hypothyroidism. Pregnancy can trigger thyroid problems — some women develop postpartum thyroiditis in the months after giving birth. Menopause can also affect thyroid function, and the symptoms of low thyroid (fatigue, weight gain, mood changes) can overlap with menopause symptoms, which sometimes delays diagnosis.

Older adults are more likely to have thyroid problems, but symptoms can be subtle or blamed on aging. An older person with low thyroid might just seem slower or more forgetful, and a doctor might not think to test the thyroid. Newborns are screened for thyroid problems at birth in most places, because untreated low thyroid in infancy can cause permanent brain damage. Children can develop thyroid problems too, though it is less common than in adults.

Frequently Asked Questions

Can you feel your thyroid if you touch your neck?

You can feel the thyroid gland itself if you know where to look — it is the soft tissue just below your Adam's apple on both sides of your windpipe. A normal thyroid is small and smooth and does not stick out. If your thyroid is enlarged or has lumps, you or a doctor may be able to feel it. Any lump or swelling in your neck should be checked by a doctor.

What foods help your thyroid work better?

Your thyroid needs iodine to make hormones, so eating iodized salt, seafood, eggs, or dairy can help. Selenium and zinc also support thyroid function — you get these from nuts, seeds, meat, and shellfish. If you have an autoimmune thyroid condition, some people find that avoiding gluten or taking supplements helps, but talk to your doctor before making big diet changes.

Can stress affect your thyroid?

Stress can trigger or worsen thyroid problems, especially autoimmune thyroid disease. Stress hormones can make your immune system more likely to attack your thyroid. Stress also affects the pituitary and hypothalamus, which control thyroid hormone release. Managing stress through sleep, exercise, or relaxation may help, but it cannot cure a thyroid condition on its own.

Is thyroid disease hereditary?

Yes, thyroid disease runs in families. If your parent or sibling has Hashimoto's disease or Graves' disease, your risk is higher. You inherit a tendency toward autoimmune thyroid disease, not the disease itself — whether you actually develop it depends on other factors like stress, infections, and hormonal changes.