Risk Factors For Thyroid Cancer: What Raises And Lowers Your Chances
A risk factor is anything that raises your chance of developing a disease such as cancer. Having one or even several risk factors does not mean you will get thyroid cancer, and plenty of people diagnosed with thyroid cancer have no known risk factors at all. This guide walks through what research says actually raises the risks of thyroid cancer, what may lower it, and where the evidence is strong versus where it is still limited. As always, talk with your own care team about what your personal risk factors mean for you.
What Raises Your Risk for Developing Thyroid Cancer?
Several factors are linked to a higher chance of developing thyroid cancer. Some, like your age or family history, cannot be changed. Others, like radiation exposure, can sometimes be avoided. Here are the risk factors with the strongest evidence behind them.
Radiation exposure, especially in childhood or adolescence: This is one of the clearest and most well-established risk factors for thyroid cancer. It includes radiation therapy given to treat other cancers or conditions in the head or neck area, such as Hodgkin lymphoma, or radiation given before a stem cell transplant. Before the 1960s, children were sometimes treated with low-dose radiation for conditions we would never use radiation for today, like acne or scalp fungal infections, and those individuals were later found to have a higher risk of thyroid cancer. The amount of risk depends on both the radiation dose and how young the person was at the time of exposure. Being exposed to radiation as an adult carries much less risk than the same exposure in childhood.
A family history of thyroid cancer: If a close relative, such as a parent, sibling, or child, has had thyroid cancer, your own risk is higher, even without a known inherited genetic syndrome in the family. That said, most people diagnosed with thyroid cancer do not have a family history of the disease, so a family history is a risk factor, not a requirement.
Inherited genetic syndromes: A handful of rare inherited conditions raise the risk of specific thyroid cancer types. Cowden syndrome (also called multiple hamartoma syndrome) raises the risk of papillary and follicular thyroid cancer, along with breast cancer and other cancers, often at a younger age than usual. Familial adenomatous polyposis, and its subtype Gardner syndrome, both caused by changes in the APC gene, raise the risk of papillary thyroid cancer along with a very high risk of colon cancer from many colon polyps. Carney complex, a rare syndrome that also causes dark skin spots and certain benign tumors, raises the risk of papillary and follicular thyroid cancer, usually at a young age.
Iodine intake, both too little and, in some settings, too much: The thyroid gland needs iodine to make thyroid hormone, and iodine levels in the diet affect thyroid cancer risk in different ways depending on the type. Follicular thyroid cancer is more common in parts of the world where diets are low in iodine. On the other hand, some evidence suggests that a diet very high in iodine may raise the risk of papillary thyroid cancer. In the United States, most people get enough iodine because it is added to table salt and other foods, so severe iodine deficiency is uncommon here.
Being female: Thyroid cancer occurs almost three times more often in women than in men, for reasons that are not fully understood. This guide uses inclusive language throughout, since anyone with a thyroid gland, regardless of sex, can develop thyroid cancer.
Age: Thyroid cancer, particularly differentiated thyroid cancer (the group that includes papillary and follicular thyroid cancer), can occur at any age, including in children and younger adults. It is most common in people in their thirties through sixties. This is somewhat unusual compared with many other cancers that mostly affect older adults, and it is one reason a new neck lump in a younger person should still be evaluated rather than dismissed because of age.
Excess body weight: People with excess body weight appear to have a higher risk of thyroid cancer than people without it, and the risk seems to rise as body mass index increases. This connection is recognized by major health organizations, but it is worth being honest that this type of evidence, based on population studies rather than a clearly proven biological mechanism, is generally considered less definitive than the evidence for radiation exposure or inherited syndromes.
Medullary thyroid carcinoma risk works differently
Medullary thyroid carcinoma (MTC) is a distinct type of thyroid cancer that arises from C cells (calcitonin-producing cells) rather than the follicular cells involved in papillary and follicular thyroid cancer, and its risk factors are different too. Roughly one quarter of MTC cases are hereditary, caused by an inherited change in a gene called RET, while the remaining three quarters are sporadic, meaning they are not inherited and occur without a known family pattern. Hereditary MTC can occur as part of multiple endocrine neoplasia type 2A (MEN2A), multiple endocrine neoplasia type 2B (MEN2B), or familial medullary thyroid carcinoma (FMTC), a form in which MTC occurs without the other tumors seen in MEN2A or MEN2B. People with MEN2A can also develop pheochromocytoma (a tumor of the adrenal gland) and parathyroid tumors, while people with MEN2B can develop pheochromocytoma along with benign growths on the lips, tongue, or lining of the digestive tract, and their MTC tends to develop earlier and behave more aggressively. Because the hereditary forms are serious and identifiable, genetic testing for RET mutations is recommended for every single person diagnosed with MTC, not just those with an obvious family history, and testing is also recommended for their close relatives, since finding a mutation early can lead to monitoring or preventive treatment before cancer develops.
Factors That May Lower Your Risk of Thyroid Cancer
There is no proven way to prevent most thyroid cancer. Unlike some other cancers where diet, exercise, or avoiding a specific substance clearly lowers risk, the evidence for thyroid cancer prevention is much more limited, and no major health organization currently recommends a specific prevention program for the general population. What follows are the areas where the evidence does support real, honest steps, even if they cannot guarantee prevention.
Radiation: The clearest actionable step is avoiding unnecessary radiation exposure to the head and neck, especially in children. This does not mean avoiding medical imaging that your doctor recommends. It means being thoughtful about imaging that is not medically necessary, and when imaging is needed, making sure it uses the lowest radiation dose that still gives a clear, useful picture. This guidance applies most strongly to children, since radiation exposure at a young age carries more risk than the same exposure later in life.
Maintaining adequate iodine intake, without going to an extreme in either direction, is another reasonable and evidence-based step. Most people in the United States already get enough iodine through iodized salt and other common foods, so this is less often something people need to actively manage here, but it remains a genuine public health principle worth knowing, especially if you follow a diet that limits iodized salt or other iodine sources.
RET mutation is linked to MEN2A, MEN2B, or familial MTC; there is a real, specific, and important action available: genetic counseling, combined with a conversation with a specialist about the timing of prophylactic thyroidectomy (surgery to remove the thyroid gland before cancer develops, done specifically to prevent MTC in someone known to carry a high-risk mutation). This is one of the few situations in all of oncology where a genetic test result can lead directly to a preventive surgery decision, and the right timing depends on the specific RET mutation involved and the risk category it falls into. Our guide on thyroid cancer screening goes into more detail on how this surveillance and decision-making process works.
Outside of these specific situations, it is worth repeating that most thyroid cancer, and especially the most common types, cannot currently be prevented through lifestyle changes, supplements, or specific diets. This can be a hard thing to hear, especially if you are looking for something concrete to do after a diagnosis in your family or a scare of your own. The honest picture is that reducing risk where it can genuinely be reduced, through avoiding unnecessary radiation and managing iodine sensibly, plus staying alert to any new neck lump or symptom described in our guide on thyroid cancer symptoms, is a more realistic and useful goal than aiming for broad prevention. If thyroid cancer runs in your family or you have questions about your own risk, your doctor or a genetic counselor can help you understand what testing, if any, makes sense for you, and our guide on questions to ask about thyroid cancer can help you prepare for that conversation.