Thyroid hormones control your metabolism, which is the rate at which every part of your body works. When your thyroid gland is working properly, your etabolism stays at a steady pace- not too fast and not too slow.

The thyroid gland is controlled by the pituitary gland (a gland in your brain). The pituitary gland makes thyroid stimulating hormone (TSH). TSH tells the thyroid gland to make more hormones if needed.

Hypothyroidism occurs when the thyroid gland does not make enough of the thyroid hormones to maintain your normal body metabolism

The most common cause of hypothyroidism is a disorder known as thyroiditis—an inflammation of the thyroid gland. The most common type of thyroiditis is called Hashimoto disease, which causes an enlarged thyroid (also called a goiter).

Hyperthyroidism results when the thyroid gland makes too much thyroid hormone. This causes your metabolism to speed up.

The most common cause of hyperthyroidism is a disorder known as Graves disease. It most often affects women between the ages of 20 and 40. A late sign of Graves disease is often a wide-eyed stare or bulging eyes. Hyperthyroidism also may result from medication. Taking too much thyroid hormone when being treated for hypothyroidism can lead to symptoms of an overactive thyroid. Lumps in the thyroid called hot nodules are another cause. These lumps produce excess thyroid hormone.