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, the time of your exposures, and the distance between you and the source of radiation.

Signs and symptoms are also 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 signs and symptoms

The initial signs and 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 signs and symptoms, a person with radiation sickness may have a brief period with no apparent illness, followed by the onset of new, more-serious symptoms.

If you've had a mild exposure, it may take hours to weeks before any signs and symptoms begin. But with severe exposure, signs and 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

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.

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 your body. Regions of the body most vulnerable to high-energy radiation are cells in the lining of your intestinal tract, including your stomach, and the blood cell-producing cells of bone marrow.

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