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. Signs and symptoms also are affected by the type of exposure — such as total or partial body and whether contamination is internal or external — and how sensitive to radiation the affected tissue is. For instance, the gastrointestinal system and bone marrow are highly sensitive to radiation.

Absorbed dose and duration of exposure

The absorbed dose of radiation is measured in a unit called a gray (Gy). Diagnostic tests that use radiation, such as an X-ray, result in a small dose of radiation — typically well below 0.1 Gy, focused on a few organs or small amount of tissue.

Signs and symptoms of radiation sickness usually appear when the entire body receives an absorbed dose of at least 1 Gy. Doses greater than 6 Gy to the whole body are generally not treatable and usually lead to death within two days to two weeks, depending on the dose and 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 when these symptoms develop is an indicator of 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.

In general, the greater your radiation exposure, the more rapid and more severe your symptoms will be.

Early symptoms of radiation sickness*
  Mild exposure (1-2 Gy) Moderate exposure (2-6 Gy) Severe exposure (6-8 Gy) Very severe exposure (8-10 Gy or higher)
Nausea and vomiting Within 6 hours Within 2 hours Within 1 hour Within 10 minutes
Diarrhea -- Within 8 hours Within 3 hours Within 1 hour
Headache -- Within 24 hours Within 4 hours Within 2 hours
Fever -- Within 3 hours Within 1 hour Within 1 hour
Later symptoms of radiation sickness*
Dizziness and disorientation --  -- Within 1 week Immediate
Weakness, fatigue Within 4 weeks Within 1-4 weeks Within 1 week Immediate
Hair loss, bloody vomit and stools, infections, poor wound healing, low blood pressure -- Within 1-4 weeks Within 1 week Immediate

* Adapted from Radiation exposure and contamination. The Merck Manuals: The Merck Manual for Healthcare Professionals.

When to see a doctor

An accident or attack that causes radiation sickness would no doubt cause a lot of attention and public concern. If such an event occurs, monitor radio, television or online reports to learn about emergency instructions for your area.

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

Oct. 06, 2012

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