Hypothyroidism generally refers to low thyroid function, which is clinically known as hypothyroidism or hypothyroidism, and is a relatively common disease at this stage. The causes of hypothyroidism are many, including thyroid disease, congenital factors, surgery, medications, iodine deficiency, and many other factors. The common delayed hypothyroidism is caused by chronic lymphocytic thyroiditis and Hashimoto’s thyroiditis, and to a lesser extent by subacute thyroiditis. If left untreated, Hashimoto’s thyroiditis can cause organic lesions in the thyroid gland, resulting in a decrease in thyroid hormone secretion and an increase in thyrotropic hormone secretion, which can lead to hypothyroidism. Subacute thyroiditis can also cause hypothyroidism due to untimely treatment. In a small number of patients, hypothyroidism is caused by congenital defects in thyroid hormone synthesis or underdeveloped thyroid tissue, which can develop in newborns or during adolescence. Some patients also suffer from excessive removal of thyroid tissue during surgery for hyperthyroidism or excessive doses of iodine 131 and thyroid medication. In addition, hypothyroidism can be caused by severe iodine deficiency, secondary hypopituitarism and hypothalamic lesions, so patients with hypothyroidism need to be systematically examined to identify the cause and then treated accordingly.