Most people do not have any known risk factors for thyroid cancer. If you do have risk factors, they can include:^{1, 2}

• A history of radiation treatments to the head, neck, or chest during childhood. Years ago, radiation was used to treat problems such as acne and fungal scalp infections and to shrink the tonsils and adenoids. Radiation exposure in adulthood does not carry the same risk.
• Exposure to high levels of radiation, such as occurred after the Chernobyl nuclear power accident in 1986. The risk is increased most for those who were younger than age 15 when they were exposed to radiation.
• Exposure to fallout from nuclear weapons testing, such as the testing that occurred in the United States during the 1950s. But the radiation exposure from the testing in the 1950s was much lower than at Chernobyl and no increased risk of thyroid cancer at this low level of exposure has been proven.²
• A family history of conditions called MEN 2a, MEN 2b, or FMTC (familial medullary thyroid carcinoma). These are caused by an abnormal gene that greatly increases the risk of getting the medullary form of thyroid cancer.
• Other inherited medical conditions, such as Gardner's syndrome and familial polyposis.
• Age. Most cases of thyroid cancer are diagnosed in people who are between the ages of 25 and 65, although it can develop at any age.
• Being female. Thyroid cancer occurs more frequently in women than it does in men.
• Being Asian.
• A diet that is too low in iodine. This is not generally a problem in the United States and Canada, because iodine is added to salt and other foods.