Thyroid nodules in most cases refer to nodular goiter, which is the result of the continued development of a simple goiter. A compensatory enlargement of the thyroid gland due to a decrease in synthesis or an increase in the demand for thyroid hormone due to a variety of causes and the secretion of excess thyrotropic hormone by the anterior pituitary gland is called a simple goiter, also known as an endemic goiter. When the lesion persists or repeatedly worsens and remits, the irregular enlargement or regeneration of the thyroid gland, gradually forming nodules, is called nodular goiter. The causes are as follows: 1. Iodine deficiency: Iodine deficiency in the living environment is the main cause of endemic goiter. Iodine is the main raw material for synthesizing thyroid hormones. If iodine intake is insufficient, the synthesis of thyroid hormones will be reduced and hypothyroidism will occur. If there is a long-term iodine deficiency, the thyroid gland will further proliferate and the iodine uptake and secretion rate of different parts of the thyroid gland will vary, and nodules will appear due to the unbalanced proliferation and recovery of each follicle. 2. Physiological factors: In women during puberty, pregnancy and menopause, the demand for thyroid hormones increases, which can also lead to goiter. 3.Disorders of synthesis and secretion of thyroxine caused by various reasons. 4.Drugs: Long-term use of thiouracil, etc. may also be the cause of goiter. 5. High iodine: Long-term consumption of water containing high iodine or use of food containing high iodine can also lead to goiter. Based on the above-mentioned causes, the state prevents its occurrence by adding iodine to the salt of residents in areas where iodine deficiency is endemic, etc.