In non-iodine deficient areas, chronic lymphocytic thyroiditis is the most common cause; in iodine deficient areas, iodine deficiency is the most common cause of hypothyroidism. There are various causes of hypothyroidism, and more than 90% of hypothyroidism patients are caused by diseases of the thyroid gland itself. The causes can be divided into: 1) inflammation of the thyroid gland; 2) surgical removal or radiation therapy; 3) iodine deficiency; and 4) other causes of hypothyroidism. Hypothyroidism caused by pituitary, hypothalamic and thyroid hormone (TH) resistance is relatively uncommon. Depending on the age and time of onset of hypothyroidism, it is clinically classified as: 1. Those who develop hypothyroidism during embryonic or infancy are called congenital hypothyroidism: also known as cretinism or cretinism. These patients usually have brain development and bone development disorders, causing obesity is relatively rare. 2, adult onset is called adult hypothyroidism, severe disease is called mucinous edema: this type of patients often have weight gain, fat deposition in the body and hyperlipidemia and other manifestations, sometimes easy to confuse with simple obesity, need to pay attention to.