I. Definition: What is thyroid cancer? Thyroid cancer accounts for 1% of all malignant tumors in the body. Except for medullary carcinoma, the vast majority of thyroid cancers originate from follicular epithelial cells. The incidence of thyroid cancer is related to region, race and gender. II. Important reasons for the high incidence of thyroid cancer 1. Diagnostic techniques and thyroid screening With the development of medical diagnostic techniques and socio-economic development, the residents’ consultation rate and disease screening rate have increased, and the detection rate of early stage disease has been enhanced. There are significant geographical differences in incidence rates: the highest in the northeast and the lowest in the south. Morbidity was significantly correlated with endocrinologist/surgeon density and significantly correlated with the use of neck ultrasound. Endocrine/surgeon density and use of ultrasound density explained the interstate variation in nail cancer. CONCLUSION: The evidence suggests that the high incidence of thyroid cancer is due to increased screening for a “reservoir of hidden disease. The benefits of therapeutic interventions triggered by increased screening are limited. Current trends in thyroid cancer growth, as reported by the New York Cancer Center and others in 2013, suggest that more occult cancers will be detected and thus treated with interventions that may not benefit patients with this potentially harmful cancer only. The overdiagnosis of thyroid cancer increases the concern in the public health field. 2. Environmental factors (1) Exposure to radiation during childhood. (2) Exposure to harmful chemicals. These substances are widely found in soil, drinking water, certain vegetables and grains. They can compete with iodine and affect the uptake of iodine by the thyroid gland, so these substances have a greater effect on those who are iodine deficient and little effect on those who have sufficient iodine. Carcinogenic substances: bromides, formaldehyde, nitrites, polycyclic aromatic hydrocarbons, volcanic ash, etc. These substances have been proved to be obviously carcinogenic. 3. Dietary factors (1) Iodine intake. Since iodine has a double-edged sword effect on the thyroid gland, iodine deficiency or excess iodine can affect the thyroid gland, so residents should maintain an adequate and appropriate level of iodine intake. (2) Diet or lifestyle. It has been proved that metabolic disorders caused by obesity can increase the risk of thyroid cancer. (1) Avoid ionizing radiation: Reduce or avoid radiation, especially during childhood (focus on radiation of medical origin). (2) Avoid iodine deficiency or excess iodine. (3) Control body weight and reduce obesity. (4) Choose a variety of foods and increase the consumption of fresh fruits and vegetables.