Hashimoto's thyroiditis is an autoimmune disease, a disorder in which the immune system turns against the body's own tissues. In people with Hashimoto's, the immune system attacks the thyroid. This can lead to hypothyroidism, a condition in which the thyroid does not make enough hormones for the body's needs.
Located in the front of your neck, the thyroid gland makes hormones that control metabolism. This includes your heart rate and how quickly your body uses calories from the foods you eat.