Radiation sickness (acute radiation syndrome) is a life-threatening condition that results from significant exposure to ionizing radiation. It’s most likely to happen after a radiological or nuclear emergency, not from medical procedures. It has a distinct order of symptoms based on the amount of exposure.
Radiation sickness, also known as acute radiation syndrome (ARS), is a life-threatening condition that results from prolonged or significant exposure to ionizing radiation to your whole body or a large portion of your body. It can lead to death within hours or several months after exposure.
Radiation sickness is generally associated with acute (sudden and severe) exposure and has a set of symptoms that appear in a predictable order. Chronic radiation exposure is usually associated with prolonged medical problems, such as cancer and premature aging. These complications may happen over a long period of time.
The severity of radiation sickness depends on the dose and the length of time over which you’re exposed. Exposure to a high, single dose over minutes to hours is more damaging than several smaller doses given over weeks or months to a small area of your body (such as with cancer therapy).
Ionizing radiation is a form of energy that removes electrons from atoms and molecules of substances that include air, water and living tissue. You can’t see ionizing radiation.
Medical diagnostic procedures rarely have radiation doses high enough to cause radiation injury. Radiation sickness happens after significant exposure to radiation, such as from exposure from a nuclear power plant accident or excessive radiation for medical treatments.
Everyone is exposed to low levels of ionizing radiation every day — usually from natural sources, such as space, earth and building materials. There are manmade sources of ionizing radiation, too. These most commonly include medical imaging tests or treatments such as X-rays, CT (computed tomography) scans and radiation therapy.
Ionizing radiation exposure that results in radiation sickness is often measured in a unit called the gray (Gy). It’s the amount of radiation that your body absorbs.
The mildest (though still harmful) form of radiation sickness happens at 1 to 6 Gy. Death is usually guaranteed at exposure of 10 Gy or more.
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Radiological or nuclear emergencies that result in radiation sickness are rare, but they can involve significant numbers of people. For example, after the Chornobyl nuclear power plant disaster in 1986, approximately 6,000 children developed thyroid cancer.
The most significant radiation exposure to a population occurred following the detonation of two atomic bombs over Japan in August 1945. It caused about 110,000 deaths from the immediate blast. Around an additional 1,000 people died over the course of 70 years after the detonation due to radiation-induced cancer.
Large doses of ionizing radiation cause cell death. Lower doses can interfere with cellular repair systems, cell growth and cell division.
The cells that are especially sensitive to high doses of radiation include cells in your bone marrow, gastrointestinal tract and skin. You typically have symptoms related to damage of these tissues first after significant exposure.
The severity of symptoms depends on:
Symptoms may begin right after exposure or over the next few days, weeks or months.
After acute exposure to a high dose of radiation, several distinct syndromes may occur, including:
Each of these syndromes has three different phases, including:
Cerebrovascular syndrome is always fatal. It happens after extremely high whole-body doses of radiation (more than 30 Gy).
The prodromal phase develops within minutes to one hour after exposure. The latent phase is nonexistent or very brief. In the overt systemic illness phase, symptoms include:
Death occurs within hours to one to two days.
GI syndrome happens after whole-body radiation doses of about 6 to 30 Gy.
Prodromal symptoms develop within about one hour after exposure and resolve within two days. The latent phase lasts four to five days.
Symptoms of the overt systemic illness phase include:
Death is common. Survivors also have the hematopoietic syndrome.
Hematopoietic syndrome happens after whole-body radiation doses of about 1 to 6 Gy and involves generalized pancytopenia. This is a deficiency of all three cellular components of your blood:
The prodromal phase is mild and may begin one to six hours after exposure, lasting 24 to 48 hours. The latent asymptomatic phase lasts about four weeks.
Symptoms of the overt phase include:
Survivors have an increased likelihood of radiation-induced cancer, including leukemia and thyroid cancer.
Radiation sickness (acute radiation syndrome) can result from direct exposure or contamination by radioactive materials.
A nuclear blast, radiation accidents and fallout from nuclear weapons testing can result in direct exposure. Contamination can result from consuming nuclear-contaminated food and water and skin contact with the nuclear material.
If someone who has been exposed to a high dose of radiation is decontaminated — their clothes are removed and their body is washed — they’re not “contagious.” You’re not at risk of radiation exposure from them because the radiation is internalized.
If someone who has been exposed to a high dose of radiation isn’t decontaminated, and you’re near them, you’re at risk for radiation exposure. First responders to nuclear emergencies, for example, are at higher risk of exposure from other people.
Healthcare providers diagnose radiation sickness using the following:
The onset, timeframe and severity of symptoms can help providers determine the radiation dose and predict the symptoms and complications.
After acute radiation exposure, providers order complete blood count (CBC) tests 24, 48 and 72 hours after exposure to estimate the initial radiation dose and prognosis. Providers may order other blood tests.
When providers suspect radioactive contamination, they test your entire body with a tool called a Geiger-Muller counter to detect and measure ionizing radiation. To detect possible internal contamination, a provider will wipe your ears, mouth and wounds with swabs that they then test with the counter. They may also test your pee and poop for radioactivity.
The treatment for radiation sickness varies based on its severity. As significant exposure usually results from radiological or nuclear emergencies, healthcare providers and first responders prioritize care based on the severity of symptoms and injuries.
Some general treatment strategies include:
There’s nothing you can do to prevent emergencies that lead to significant radiation exposure and radiation sickness. But there are steps you can take if a nuclear emergency happens, including:
The prognosis (outlook) of radiation sickness depends on several factors, including:
Radiation sickness is often fatal. The time to death decreases as the dose of radiation decreases.
Cerebrovascular syndrome is always fatal within hours to days after exposure.
Death usually occurs within two days to several weeks for those who have gastrointestinal syndrome.
For people with hematopoietic syndrome, death may happen within four to eight weeks due to an infection or a significant hemorrhage (bleeding).
People who were exposed to whole-body doses of less than 2 Gy usually fully recover within one month. But long-term complications, such as cancer, may occur.
A note from Cleveland Clinic
Radiation sickness is a life-threatening condition that happens after significant radiation exposure. While there’s nothing you can do to prevent it, there are steps you can take if you’ve been exposed after a radiological or nuclear emergency. If possible, decontaminate yourself by removing your clothes and washing your body. Then, get medical care as soon as possible.
Last reviewed by a Cleveland Clinic medical professional on 10/24/2022.
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