Thyroiditis refers to inflammation of the thyroid gland and is significantly more common in women than in men, but there is no significant difference in the clinical presentation between men and women. Most thyroiditis is insidious, with no specific symptoms in the early stages, making it difficult to detect, and some patients even remain undetected, known as asymptomatic first thyroiditis. In addition to the painful enlargement caused by the inflammation of the thyroid gland itself, patients who are detected usually go through a process of transformation from hyperthyroidism to hypothyroidism. Because the inflammation destroys the thyroid follicles, stored thyroid hormones leak into the bloodstream and symptoms of hyperthyroidism appear, but because the destroyed follicles cannot continue to secrete, they later turn into hypothyroidism due to insufficient thyroid hormones. Some types of thyroiditis can restore follicular function, but others can become lifelong hypothyroidism. Postpartum thyroiditis is also a variant of painless thyroiditis. Painless thyroiditis has a mild infiltration of lymphocytes in the thyroid gland, with only a focal infiltrate that manifests as transient reversible thyroid follicular destruction. In half of the patients, the thyroid gland is mildly enlarged, diffuse, hard in texture, and without local tenderness. The thyrotoxicosis in this disease is due to the destruction of thyroid follicles by inflammation and leakage of thyroid hormones into the circulation. Most patients are not even detected because of mild symptoms. Therefore, there is no particular difference in the clinical presentation of thyroiditis between men and women, differing only in the specific type of thyroiditis known as postpartum thyroiditis, with most of the remaining presentations being the same.