The thyroid gland stops working properly when your immune system attacks it, when you don't get enough iodine, or when something disrupts the hormones that control it

Your thyroid produces hormones that regulate how fast your body burns calories, how your heart beats, and how warm you feel. When the gland itself is damaged, when your immune system turns against it, or when your pituitary gland (which sits in your brain and tells the thyroid what to do) sends the wrong signals, thyroid hormone levels drop or spike. The result is either hypothyroidism — too little thyroid hormone — or hyperthyroidism — too much.

Most thyroid problems fall into a few clear categories based on what goes wrong. Understanding which one you have matters because the cause shapes the treatment and what happens next.

Key Takeaways

  • Hashimoto's disease, an autoimmune condition where your immune system attacks the thyroid, is the most common cause of hypothyroidism in iodine-sufficient countries.
  • Graves' disease, another autoimmune condition, causes hyperthyroidism by making the thyroid overproduce hormones.
  • Iodine deficiency remains the leading preventable cause of thyroid problems worldwide, though it is rare in countries with iodized salt.
  • Pregnancy, certain medications, radiation, and surgery can all trigger or worsen thyroid dysfunction.
  • The pituitary gland controls the thyroid through hormones, so problems in the pituitary can cause thyroid symptoms even when the thyroid itself is healthy.

Autoimmune attacks on the thyroid gland

Hashimoto's thyroiditis is an autoimmune disease where your immune system mistakenly identifies thyroid cells as foreign and destroys them. This is the most common cause of hypothyroidism in North America and Europe. Your body produces antibodies against thyroid peroxidase (TPO) and thyroglobulin — proteins the thyroid needs to function. Over months or years, enough thyroid tissue is damaged that hormone production falls below what your body needs.

Hashimoto's runs in families and is more common in women than men. It often develops slowly, so you might not notice symptoms for a long time. A blood test showing high TPO antibodies and low thyroid hormone confirms the diagnosis.

Graves' disease is the opposite: your immune system produces antibodies that tell the thyroid to make too much hormone. These antibodies bind to thyroid receptors and trigger constant hormone release, causing hyperthyroidism. Graves' also runs in families and is more common in women. It can develop suddenly and cause noticeable symptoms within weeks — rapid heartbeat, weight loss, heat sensitivity, and tremors.

Iodine deficiency and thyroid function

Your thyroid needs iodine to make thyroid hormones. Without it, the gland cannot produce enough hormone even if it is structurally healthy. Iodine deficiency is the leading preventable cause of thyroid problems worldwide, affecting roughly two billion people in regions where iodized salt is not widely used.

In countries with iodized salt programs — including the United States, Canada, and most of Europe — severe iodine deficiency is rare. But mild deficiency can still occur in people who avoid salt, eat mostly processed foods made with non-iodized salt, or live in areas where soil iodine is naturally low. Pregnancy increases iodine demand, so deficiency during pregnancy can affect fetal brain development.

When iodine is scarce, the thyroid enlarges (a condition called goiter) as it tries to capture more iodine from the bloodstream. The gland may grow visibly large but still fail to produce enough hormone.

Pregnancy, medications, and hormonal changes

Pregnancy triggers major changes in thyroid function. The thyroid naturally enlarges slightly and produces more hormone during pregnancy to meet increased metabolic demand. Some women develop postpartum thyroiditis — inflammation of the thyroid in the months after delivery — which can cause temporary hyperthyroidism followed by hypothyroidism as the inflammation resolves.

Several medications interfere with thyroid function. Lithium, used to treat bipolar disorder, can cause hypothyroidism by blocking iodine uptake. Amiodarone, a heart rhythm medication, contains high amounts of iodine and can trigger either hypothyroidism or hyperthyroidism depending on your baseline iodine status. Interferon-alpha and some cancer immunotherapy drugs can activate autoimmune thyroid disease. If you take any of these, your doctor monitors thyroid function with regular blood tests.

Estrogen therapy and hormone replacement therapy can affect how much thyroid hormone your body needs, so thyroid levels may shift when you start or stop these treatments.

Radiation, surgery, and physical damage to the thyroid

Radiation to the head, neck, or chest — whether from cancer treatment, nuclear accidents, or medical imaging — can damage thyroid cells and cause hypothyroidism years later. The risk increases with higher radiation doses and with exposure during childhood, when the thyroid is still developing.

Thyroid surgery to remove part or all of the gland (usually because of cancer, nodules, or severe hyperthyroidism) causes hypothyroidism if enough tissue is removed. Radioactive iodine treatment, used for Graves' disease and some thyroid cancers, destroys thyroid tissue and almost always leads to hypothyroidism over time.

Inflammation from viral infections can also damage the thyroid temporarily. Subacute thyroiditis, usually triggered by a viral infection, causes the thyroid to release stored hormone suddenly (causing hyperthyroidism symptoms) followed by a period of low hormone production as the gland recovers.

Pituitary and hypothalamus problems

Your thyroid does not work independently. The pituitary gland, a pea-sized structure at the base of your brain, produces thyroid-stimulating hormone (TSH), which tells the thyroid how much hormone to make. The hypothalamus, another brain region, controls the pituitary. If either the pituitary or hypothalamus is damaged or diseased, thyroid hormone levels can drop even though the thyroid itself is healthy.

Pituitary tumors, head injuries, brain surgery, or radiation to the brain can all disrupt TSH production. This type of hypothyroidism is called central hypothyroidism and is less common than primary hypothyroidism (where the thyroid itself is damaged). The treatment is the same — thyroid hormone replacement — but the underlying cause is in the brain, not the gland.

Other causes and risk factors

Certain conditions increase thyroid disease risk. Type 1 diabetes and celiac disease often occur alongside autoimmune thyroid disease because they share genetic and immune factors. Polycystic ovary syndrome (PCOS) is associated with higher rates of thyroid antibodies. Down syndrome and Turner syndrome both carry increased thyroid disease risk.

Age matters: thyroid disease becomes more common as you get older, particularly in women over 60. Family history is a strong predictor — if a parent or sibling has thyroid disease, your risk is higher. Stress does not directly cause thyroid disease, but severe or prolonged stress may trigger autoimmune thyroid disease in genetically susceptible people.

Some foods contain compounds called goitrogens that can interfere with iodine absorption if eaten in very large amounts — these include cruciferous vegetables like cabbage and broccoli, and soy products. For most people eating a normal diet, these foods pose no risk. But in regions with iodine deficiency, high consumption of goitrogen-rich foods can worsen thyroid problems.

Frequently Asked Questions

Can stress cause thyroid problems?

Stress alone does not cause thyroid disease, but severe or chronic stress may trigger autoimmune thyroid disease in people who are genetically predisposed. If you have a family history of thyroid disease, managing stress through exercise, sleep, and relaxation may help reduce risk, though it cannot prevent disease entirely.

Is thyroid disease hereditary?

Autoimmune thyroid diseases like Hashimoto's and Graves' run in families because they share genetic risk factors. Having a parent or sibling with thyroid disease increases your risk, but it does not may provide you will develop it. Environmental triggers also play a role.

Can diet alone fix thyroid problems?

Diet cannot reverse autoimmune thyroid disease or cure hyperthyroidism, but adequate iodine intake supports thyroid function. If you have hypothyroidism from any cause, thyroid hormone medication is necessary. Eating a balanced diet with sufficient iodine, selenium, and zinc supports overall thyroid health but is not a substitute for medical treatment.

Why do women get thyroid disease more often than men?

Women are five to eight times more likely to develop autoimmune thyroid disease, though the exact reason is not fully understood. Sex hormones, X chromosome genetics, and differences in immune response all likely play a role. Pregnancy and hormonal changes can also trigger or worsen thyroid disease in women.

Does having one autoimmune disease mean I will get thyroid disease?

People with type 1 diabetes, celiac disease, or rheumatoid arthritis have higher rates of autoimmune thyroid disease than the general population, but most do not develop it. If you have another autoimmune condition, periodic thyroid screening may catch thyroid disease early, but it is not inevitable.