Experts do not know the exact cause of thyroid nodules. But they do know that people who have been exposed to radiation have a greater chance of developing thyroid nodules. Exposure to environmental radiation or past radiation treatment to the head, neck, and chest (especially during childhood) raises your risk for thyroid nodules.

Experts know that thyroid nodules run in families. This means you are more likely to have a thyroid nodule if one of your parents has had a thyroid nodule.

Also, if you have another thyroid condition (such as goiter), you may have a greater chance of developing thyroid nodules.