Radiation Health Effects
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Acute Radiation Syndrome from Large Exposures
A very high level of radiation exposure delivered over a short period of time can cause symptoms such as nausea and vomiting within hours and can sometimes result in death over the following days or weeks. This is known as acute radiation syndrome, commonly known as “radiation sickness.”
It takes a very high radiation exposure to cause acute radiation syndrome—more than 0.75 (75 in a short time span (minutes to hours). This level of radiation would be like getting the radiation from 18,000 chest x-rays distributed over your entire body in this short period. Acute radiation syndrome is rare, and comes from extreme events like a nuclear explosion or accidental handling or rupture of a highly radioactive source.
Radiation Exposure and Cancer Risk
Exposure to low-levels of radiation does not cause immediate health effects, but can cause a small increase in the of cancer over a lifetime. There are studies that keep track of groups of people who have been exposed to radiation, including atomic bomb survivors and radiation industry workers. These studies show that radiation exposure increases the chance of getting cancer, and the risk increases as the dose increases: the higher the dose, the greater the risk. Conversely, cancer risk from radiation exposure declines as the dose falls: the lower the dose, the lower the risk.
Radiation doses are commonly expressed in millisieverts (international units) or rem (U.S. units). A dose can be determined from a one-time radiation exposure, or from accumulated exposures over time. About 99 percent of individuals would not get cancer as a result of a one-time uniform whole-body exposure of 100 millisieverts (10 rem) or lower.1 At this dose, it would be extremely difficult to identify an excess in cancers caused by radiation when about 40 percent of men and women in the U.S. will be diagnosed with cancer at some point during their lifetime.
Risks that are low for an individual could still result in unacceptable numbers of additional cancers in a large population over time. For example, in a population of one million people, an average one-percent increase in lifetime cancer risk for individuals could result in 10,000 additional cancers. The EPA sets regulatory limits and recommends emergency response guidelines well below 100 millisieverts (10 rem) to protect the U.S. population, including sensitive groups such as children, from increased cancer risks from accumulated radiation dose over a lifetime.
Sensitive Populations
Children and fetuses are especially sensitive to radiation exposure. The cells in children and fetuses divide rapidly, providing more opportunity for radiation to disrupt the process and cause cell damage. EPA considers differences in sensitivity due to age and sex when revising radiation protection standards.