Subacute thyroiditis is usually caused by viral infections. When the lesions are extensive, thyroid hormones and non-hormonal iodinated proteins within the follicles are released into the circulation in large quantities on a transient basis, and in addition to the systemic manifestations of the infections, some patients may also suffer from thyrotoxicosis within a few weeks after the disease, and may be uncomfortable. Viral infections such as coxsackie virus, mumps virus, and influenza virus can cause subacute thyroiditis, in which the thyroid follicles are destroyed by inflammation, and thyroid hormones stored inside are released into the blood circulation, and symptoms of hyperthyroidism, such as fever, tachycardia, and irritability, may occur. When the thyroid hormone within the thyroid follicles is depleted due to the destruction of the tissue structure by infection, and before the thyroid follicular tissue is repaired, the serum thyroid hormone concentration decreases to the level of hypothyroidism, which may also clinically turn into hypothyroidism. Symptoms of hypothyroidism such as bradycardia, fatigue, and memory loss may occur. Therefore, the patient may experience discomfort all over the body. Patients with subacute thyroiditis should go to the hospital in time.