Thyroiditis is a group of diseases characterized by inflammation of the thyroid gland. Different types of thyroiditis have different etiologies and different prognoses. Take a few common types of thyroiditis as examples: Subacute thyroiditis: also known as granulomatous thyroiditis and giant cell thyroiditis. It is a self-limiting thyroiditis associated with viral infections such as influenza virus, coxsackievirus, adenovirus, and mumps virus. 10%-20% of patients may have autoantibodies to the thyroid gland found in the subacute phase. This type of thyroiditis is self-limiting and may have transient hyperthyroidism, but the majority of symptoms can be cured in a few days and usually leave no residual effects. Autoimmune thyroiditis: This is a large group of thyroiditis associated with an autoimmune response. Their common features are the presence of serum antibodies against the thyroid gland itself and the presence of infiltrating lymphocytes in the thyroid gland, but the degree of thyroid destruction is not necessarily proportional to the symptoms of hypothyroidism. Common types of the disease include: Hashimoto’s thyroiditis, atrophic thyroiditis, quiet thyroiditis, postpartum thyroiditis, medicated thyroiditis, and Hashimoto’s thyrotoxicosis. These thyroid infections are difficult to cure and can only be treated symptomatically. The duration of the disease varies, but most will turn into lifelong hypothyroidism. Lifelong thyroid hormone replacement therapy is required. Painless thyroiditis: The infiltration of lymphocytes in the thyroid gland is mild, with only focal infiltrates that manifest 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 of this disease is due to the destruction of thyroid follicles by inflammation and leakage of thyroid hormones into the circulation. Postpartum thyroiditis is also a variant of painless thyroiditis. This type of thyroiditis has mild lesions and does not even require treatment if there are no clinical symptoms. Acute septic thyroiditis: This is a rare or uncommon inflammation of the thyroid gland, mainly in children, due to abnormal development of the thyroid gland or other abnormalities in the neck, followed by bacterial