Radiation sickness is damage to the body caused by a large dose of radiation often received over a short time. This is called acute radiation sickness. The amount of radiation absorbed by the body, called the absorbed dose, determines how bad the illness will be.

Radiation sickness also is called acute radiation syndrome or radiation poisoning. Radiation sickness is not caused by common medical imaging tests that use low-dose radiation, such as X-rays, CT scans and nuclear medicine scans.

Although radiation sickness is serious and often fatal, it's rare. Since the atomic bombings of Hiroshima and Nagasaki, Japan, during World War II, most cases of radiation sickness have occurred after nuclear industrial accidents, such as the 1986 fire that damaged the nuclear power plant at Chernobyl, Ukraine.

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The severity of radiation sickness symptoms depends on how much radiation you've absorbed. How much you absorb depends on the strength of the radiated energy, the time of your exposures, and the distance between you and the source of radiation.

Symptoms also are affected by the type of exposure, such as total or partial body. The severity of radiation sickness also depends on how sensitive the affected tissue is. For instance, the gastrointestinal system and bone marrow are highly sensitive to radiation.

Initial symptoms

The first symptoms of treatable radiation sickness are usually nausea and vomiting. The amount of time between exposure and when these symptoms develop is a clue to how much radiation a person has absorbed.

After the first round of symptoms, a person with radiation sickness may have a brief period with no noticeable illness, followed by the onset of new, more-serious symptoms.

If you've had a mild exposure, it may take hours to weeks before symptoms begin. But with high exposure, symptoms can begin minutes to days after exposure.

Possible symptoms include:

  • Nausea and vomiting.
  • Diarrhea.
  • Headache.
  • Fever.
  • Dizziness and disorientation.
  • Weakness and fatigue.
  • Hair loss.
  • Bloody vomit and stools from internal bleeding.
  • Infections.
  • Low blood pressure.

When to see a doctor

An accident or attack that causes radiation sickness would lead to a lot of attention and public concern. If such an event happens, listen to radio, television or online reports to learn about emergency instructions for your area.

If you know you've been overexposed to radiation, seek emergency medical care.


Radiation sickness is caused by being exposed to a high dose of radiation. Radiation is the energy released from atoms as either a wave or a tiny particle of matter.

Radiation sickness happens when high-energy radiation damages or destroys certain cells in the body. Areas of the body most at risk of being affected by high-energy radiation are the bone marrow cells and the lining of the intestinal tract.

Risk factors

Being exposed to a source of high-dose radiation increases the risk of radiation sickness. Sources of high-dose radiation include:

  • An accident at a nuclear industrial facility.
  • An attack on a nuclear industrial facility.
  • A small radioactive device going off.
  • An explosive device that sends out radioactive material. This is called a dirty bomb.
  • A nuclear weapon going off.


Having radiation sickness can contribute to both short-term and long-term mental health problems, such as grief, fear and anxiety about:

  • Experiencing a radioactive accident or attack.
  • Mourning friends or family who haven't survived.
  • Dealing with the uncertainty of a mysterious and potentially fatal illness.
  • Worrying about the eventual risk of cancer due to radiation exposure.


In the event of a radiation emergency, listen to the radio or watch television to hear what protective actions local, state and federal authorities recommend. Those actions depend on the situation, but you will be told to either stay in place or evacuate your area.

Shelter in place

If you're advised to stay where you are, whether you're at home or work or elsewhere, do the following:

  • Close and lock all doors and windows.
  • Turn off fans, air conditioners and heating units that bring air in from outside.
  • Close fireplace dampers.
  • Bring pets indoors.
  • Move to an inner room or basement.
  • Stay tuned to your emergency response network or local news.
  • Stay put for at least 24 hours.


If you're advised to evacuate, follow the instructions provided by your local authorities. Try to stay calm and move quickly and in an orderly manner. Travel lightly, but take supplies, including:

  • Flashlight.
  • Portable radio.
  • Batteries.
  • First-aid kit.
  • Necessary medicines.
  • Sealed food, such as canned foods, and bottled water.
  • Manual can opener.
  • Cash and credit cards.
  • Extra clothes.

Be aware that most emergency vehicles and shelters won't accept pets. Take them only if you're driving your own vehicle and going someplace other than a shelter.

Feb. 13, 2024
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