Because all people in the United States who were alive since 1951 received some  radiation exposure from fallout, some people may have an increased risk of cancer from this exposure, in particular, thyroid cancer. CDC and NCI scientists believe that although the potential for developing thyroid cancer from exposure to global fallout is small, it is important for people to be aware of the risks.

Iodine-131, called "I-131," which exposes the thyroid gland for about 2 months after each nuclear test, was the most important harmful radioactive material (isotope) in global fallout. People exposed to I-131, especially during childhood, may have an increased risk of thyroid disease, including thyroid cancer many years later. Thyroid cancer is uncommon and is usually curable. NCI has more information about I-131 and thyroid disease at its Web site at www.cancer.gov/i131/.

Other radioactive materials in fallout, such as strontium-90, can affect a person’s bone marrow and lead to an increased risk for leukemia. However all studies have shown the risk to be very small.  Scientists continue to study the risks from exposure to these isotopes and others.