Radiation sickness (also called acute radiation syndrome) happens when a person is exposed to large amounts of radiation all at once.

Exposure to small amounts of radiation—like from an X-ray or CT scan—doesn't cause any symptoms. But exposure to large amounts of radiation all at once—like from a nuclear explosion—may cause radiation sickness and death.

Symptoms of radiation sickness may include:

• Nausea, vomiting, and diarrhea.
• Fever.
• Fatigue.
• Feeling weak, faint, or dizzy.
• Hair loss.
• Skin redness, itching, swelling, or burns.
• Pain.
• Seizures.

People who have been exposed to large amounts of radiation and have these symptoms need to see a doctor right away.