Radiation sickness is usually defined as damage to the body caused by a very large dose of radiation often received over a short period of time (acute). The amount of radiation absorbed by the body — the absorbed dose — determines how sick you'll be.

Radiation sickness is also called acute radiation sickness, acute radiation syndrome or radiation poisoning. Common exposures to low-dose radiation, such as X-ray examinations, do not cause radiation sickness.

Although radiation sickness is serious and often fatal, it's very rare. Since the atomic bombings of Hiroshima and Nagasaki, Japan, during World War II, most cases of radiation sickness have happened after nuclear industrial accidents, such as the 1986 nuclear reactor accident at a power station in Chernobyl, Ukraine.

The terrorist attacks on the United States in 2001 along with other acts of terrorism around the world have caused some to worry about terrorists' using radioactive devices that could expose many people and cause radiation sickness and deaths.

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

Absorbed dose and duration of exposure
The absorbed dose of radiation is measured in a unit called a gray (Gy). An example of a safe radiation exposure is a conventional dental X-ray, which results in an absorbed dose to the jaw of about 0.0025 Gy. A typical whole-body computerized tomography (CT) scan, a type of X-ray exam, results in an average whole-body dose of about 0.012 Gy.

Signs and symptoms of radiation sickness usually appear with absorbed doses to the whole body of at least 1 Gy. Doses greater than 8 Gy are generally not treated successfully and usually result in death within two days to two or three weeks depending on the duration of the exposure.

Initial signs and symptoms
The initial signs and symptoms of treatable radiation sickness are usually nausea and vomiting. The amount of time between exposure and the onset of these symptoms is, in fact, a relatively reliable indicator of how much radiation a person has absorbed.

After the initial onset of signs and symptoms, a person with radiation sickness then experiences a brief period of a few days with no apparent illness. This period precedes the onset of signs and symptoms indicating more serious illness.

Mild radiation sickness
Signs and symptoms resulting from an acute absorbed dose of 1 to 2 Gy may include:

• Nausea and vomiting within 24 to 48 hours
• Headache
• Fatigue
• Weakness

Moderate radiation sickness
With an acute absorbed dose of 2 to 3.5 Gy, a person may experience:

• Nausea and vomiting within 12 to 24 hours
• Fever
• Hair loss
• Infections
• Vomiting blood
• Bloody stool
• Poor wound healing
• Any signs and symptoms associated with a lower absorbed dose

Moderate radiation sickness can be fatal to those most sensitive to radiation exposure.

Severe radiation sickness
An absorbed dose of 3.5 to 5.5 Gy can result in the following signs and symptoms:

• Nausea and vomiting less than one hour after exposure to radiation
• Diarrhea
• High fever
• Any signs and symptoms associated with a lower absorbed dose

Severe radiation sickness is fatal about half the time.

Very severe radiation sickness
A person with an absorbed dose greater than 5.5 to 8 Gy can have the following signs and symptoms:

• Nausea and vomiting less than 30 minutes after exposure to radiation
• Dizziness
• Disorientation
• Low blood pressure (hypotension)
• Any signs and symptoms associated with a lower absorbed dose

Very severe radiation sickness is often fatal.

Radiation is the energy released from atoms as either a wave or a tiny particle of matter. Radiation sickness is caused by exposure to a high dose of radiation, such as a high dose of radiation received during an industrial accident. Common exposures to low-dose radiation, such as X-ray examinations, do not cause radiation sickness.

Sources of high-dose radiation
Possible sources of high-dose radiation include the following:

• An accident at a nuclear industrial facility
• An attack on a nuclear industrial facility
• Detonation of a small radioactive device
• Detonation of a conventional explosive device that disperses radioactive material (dirty bomb)
• Detonation of a standard nuclear weapon

Radiation sickness occurs when high-energy radiation damages or destroys certain cells in the body. Regions of the body most vulnerable to high-energy radiation are cells in the lining of the stomach and intestinal tract and the blood cell producing cells of bone marrow.

An accident or attack that causes radiation sickness would no doubt cause a lot of panic. If such an event were to occur, you should monitor radio, television or online broadcasts to learn about emergency instructions for your area. If you know you've been exposed to radiation, you should seek emergency medical care.

When a person has experienced known or probable exposure to high-energy radiation from an accident or attack, medical personnel will take a number of steps to determine the absorbed radiation dose. This information is essential for determining how severe the illness is likely to be, which treatments to use and whether a person is likely to survive. Information important for determining an absorbed dose includes:

• Known exposure. Details about distance from the source of radiation and duration of exposure can help provide a rough estimate of the severity of radiation sickness.
• Vomiting and other symptoms. The time between radiation exposure and the onset of vomiting is a fairly accurate screening tool to estimate absorbed radiation dose. The shorter the time before the onset of this sign, the higher the dose is. The severity and timing of other signs and symptoms may also help medical personnel determine the absorbed dose.
• Blood tests. Frequent blood tests over several days enable medical personnel to look for drops in disease-fighting white blood cells and abnormal changes in the DNA of blood cells. These factors indicate the degree of bone marrow damage, which is determined by the level of an absorbed dose.
• Dosimeter. A device called a dosimeter can measure the absorbed dose of radiation but only if it was exposed to radiation at the same time as the person was exposed.
• Survey meter. A device such as a Geiger counter can be used to survey people to determine the body location of radioactive particles.
• Type of radiation. A part of the larger emergency response to a radioactive accident or attack would include identifying the type of radiation people have been exposed to. This information would guide some decisions for treating people with radiation sickness.

Radiation sickness itself wouldn't cause long-term medical problems for those who survive the illness. However, the radiation exposure that caused the immediate radiation sickness would significantly increase a person's risk of developing cancer later in life.

Having radiation sickness could also contribute to both short-term and long-term psychological disorders, such as generalized anxiety disorder, major depression or post-traumatic stress disorder. Mental health problems may stem from the fear and anxiety of:

• Experiencing a radioactive accident or attack
• Grieving 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

The treatment goals for radiation sickness are to prevent further radioactive contamination, treat damaged organs, reduce symptoms, and manage pain.

Decontamination
Decontamination is the removal of as much external radioactive particles as possible. Removing clothing and shoes eliminates about 90 percent of external contamination. Gently washing with water and soap removes additional radiation particles from the skin. Decontamination prevents further distribution of radioactive materials and lowers the risk of internal contamination from inhalation, ingestion or open wounds.

Treatment for damaged bone marrow
A protein called granulocyte colony-stimulating factor, which promotes the growth of white blood cells, may counter the effect of radiation sickness on bone marrow. Treatment with this protein-based medication, which includes filgrastim (Neupogen) and pegfilgrastim (Neulasta), may increase white blood cell production and help prevent subsequent infections.

If you have severe damage to bone marrow, you may also receive transfusions of red blood cells or blood platelets.

Treatment for internal contamination
Some treatments may reduce damage to internal organs caused by radioactive particles. Medical personnel would use these treatments only if you've been exposed to a specific type of radiation. These treatments include the following:

• Potassium iodide is a nonradioactive form of iodine. Because iodine is essential for proper thyroid function, the thyroid becomes a "destination" for iodine in the body. If you have internal contamination with radioactive iodine (radioiodine), your thyroid will absorb radioiodine just as it would other forms of iodine. Treatment with potassium iodide may fill "vacancies" in the thyroid and prevent absorption of radioiodine. The radioiodine is eventually cleared from the body in urine.
• Prussian blue, a type of dye, binds to particles of radioactive elements known as cesium and thallium. The radioactive particles are then excreted in feces. This treatment speeds up the elimination of the radioactive particles and reduces the amount of radiation cells may absorb.
• Diethylenetriamine pentaacetic acid (DTPA) is a substance that binds to metals. DTPA binds to particles of the radioactive elements plutonium, americium and curium. The radioactive particles pass out of the body in urine, thereby reducing the amount of radiation absorbed.

Supportive treatment
If you have radiation sickness, you may receive additional medications or interventions to treat:

• Bacterial infections
• Headache
• Fever
• Diarrhea
• Nausea and vomiting
• Dehydration

End-of-life care
A person who has absorbed large doses of radiation (8 Gy or greater) has little chance of recovery. Depending of the severity of illness, death can occur within two days or two to three weeks. People with a lethal radiation dose will receive medications to control pain, nausea, vomiting and diarrhea. They may also benefit from psychological or pastoral care.