What Causes Hypothyroidism?

What is the most common cause of hypothyroidism?

Hashimoto's disease is the top cause in the US and other regions with adequate iodine in the diet. The immune system produces antibodies that attack the gland and progressively damage its ability to make hormone. It is far more common in women, runs in families, and can coexist with other autoimmune conditions. The typical finding is a rising TSH together with positive antibodies on a thyroid panel.

How does Hashimoto's disease cause low thyroid function?

In Hashimoto's, an autoimmune thyroiditis, white blood cells and antibodies slowly attack thyroid tissue and destroy hormone-producing cells over months and years. That is why symptoms appear gradually rather than all at once. The laboratory signature is positive TPO antibodies with a climbing TSH as the output falls. Knowing the autoimmune cause matters because it can travel with thyroid-related autoimmune conditions elsewhere in the body.

Can surgery or medicines cause it?

• Thyroid surgery — removing part or all of the gland
• Radioactive iodine — the standard fix for Graves' disease, it destroys thyroid tissue on purpose
• Neck radiation — used for lymphoma or head-and-neck cancer
• Medication — lithium and amiodarone are the usual suspects

These causes are permanent, but a daily replacement hormone restores normal thyroid function and keeps symptoms at bay. The common thread is that the gland itself is lost or muted, so no amount of lifestyle change brings it back — hormone pills take over that job instead.

What is postpartum thyroiditis?

After a pregnancy, the immune system can flare and inflame the thyroid. It often starts with a brief overactive phase, then moves into a hypothyroid phase that lasts weeks to months. Roughly 5–10% of pregnancies are affected, and some women never fully regain function. If it happened once, recurrence with a later pregnancy is more likely. Because many resolve, a repeat TSH around the six-month mark helps the clinician decide.

What are the symptoms of hypothyroidism?

Low thyroid slows the whole body down: fatigue, weight gain, cold hands and feet, constipation, dry skin, hair thinning, and a low mood. Many people dismiss these as stress or aging. The same complaints can come from anemia, a vitamin shortage, or sleep problems. That is exactly why a blood test, not a symptom guess, is how the true underlying condition gets confirmed and treatment begins.