Allergic thyroiditis is a condition that involves inflammation of the thyroid gland. This inflammation is caused by an allergic reaction, which results in the immune system attacking the thyroid gland. There are many synonyms for this condition, including autoimmune thyroiditis, Hashimoto's thyroiditis, and chronic lymphocytic thyroiditis. These terms describe the same condition, but they may be used by different medical professionals or in different contexts. Regardless of the term used, allergic thyroiditis can cause a range of symptoms, including fatigue, weight gain, and cold sensitivity. Treatment typically involves hormone replacement therapy and medication to manage inflammation.