It is an indisputable fact that the incidence of thyroid cancer has shown a continuous increase worldwide, but as with other tumors, the reasons why there has been a high incidence in recent years have been plaguing the academic community and deserve further exploration. The improvement of diagnostic techniques is considered to be the primary reason for the increased detection rate, and many literatures suggest that the increase in thyroid cancer incidence may be related to the development of medical diagnostic techniques and the increased sensitivity of screening techniques. It is well known that thyroid cancer mainly presents as thyroid nodules in the early stage, and in the past, thyroid nodules were mainly detected by physical examination of clinicians by touch, which usually could only detect larger nodules, therefore, thyroid nodules might have to grow larger, for example, to a diameter of 25px or more before they could be detected, so the sensitivity was low. Since the 1990s, diagnostic techniques such as high-resolution thyroid ultrasound and fine-needle aspiration biopsy (FNAb) have been widely used and the diagnostic sensitivity has increased dramatically. Nowadays, nodules of 2-3 mm can be detected by high-resolution ultrasound in many hospitals, and FNAb examination of tiny, suspected malignant nodules under ultrasound guidance makes thyroid cancer easy to be detected at an early stage. The prevalence of micro/focal thyroid cancer cannot be ignored. It is the improved diagnostic techniques that have brought about not only the ease of early detection of thyroid cancer, but also the proliferation of micro/focal thyroid cancers <1 cm in diameter. Although most of this change in the literature is a retrospective analysis of surgical pathology of thyroid nodules, there is no shortage of prospective reports. For example, the results of a national, non-cohort, prospective study conducted in Denmark between 1996 and 2008 showed a consistent increase in the annualized incidence of microscopic papillary thyroid carcinoma. Incidental (accidental, occult) thyroid cancer has increased due to the widespread use of ultrasound, CT, MRI, and other screening techniques, which have increased the rate of accidental detection of thyroid cancer to 67%, 16%, and 9%, respectively. People often find thyroid cancer accidentally when they perform various imaging examinations for other diseases. With socioeconomic development, the population has become significantly more health-conscious and pays more attention to early screening of diseases. The incidence of thyroid cancer is higher among people with more family income, higher education level, and holding a more comprehensive percentage of health insurance. The reasons for this are not unrelated to the implementation of health screening and early detection of the disease. However, there are other researchers who do not agree with these views. Some studies have found that the incidence of thyroid cancer >4 cm in diameter has likewise increased significantly over the past 30 years, and the increase in patients with such larger tumors and more advanced disease seems not to be entirely attributable to improved diagnostic techniques, and improved medical conditions. Hashimoto’s thyroiditis, both classical and non-classical cases, is common in clinical practice. The association of Hashimoto’s thyroiditis with thyroid cancer has long been noted, given that chronic inflammation can lead to tumor formation. History of exposure to ionizing radiation is a recognized risk factor for the development of thyroid cancer, such as a significantly higher incidence of thyroid cancer among residents of areas contaminated by nuclear radiation from the atomic bombings in Japan and the Chernobyl nuclear leak in the former Soviet Union. The effect of changes in iodine intake on thyroid cancer has also been known for many years, with a higher proportion of poorly differentiated thyroid cancers occurring when iodine nutrition levels are low, while increased iodine intake is more likely to occur in well-differentiated papillary cancers. In addition, many environmental factors, including environmental pollutants, such as PBDEs and excessive exposure to diagnostic radiological imaging may also contribute to the increased incidence of thyroid cancer. Thyroid cancer has become common in the population in recent years and, like a number of other chronic non-communicable diseases, is becoming a serious public health concern. In the face of such changes, there is still a long way to go, both in terms of spreading public awareness of disease prevention and treatment, and in terms of in-depth academic research on disease diagnosis and treatment from the basic to the clinical level.