Affects of acute radiation syndrome (ARS), computer artwork. ARS occurs when the body is exposed to radiation in excess of four sieverts (the biological dose equivalent of radiation). The first organ affected is the stomach (pink, with glowing sphere), causing vomiting, next are the intestines (centre bottom), causing diarrhoea. The bone marrow is also affected, leading to a reduction in the number of red and white blood cells that are produced. Damage to blood vessels in the liver (centre left) and kidneys (one at right of stomach) lead to the build up of toxic substances in the blood. Inflammation of lung (light pink) tissue causes difficulty breathing. Lesions also occur in the brain (top). Cases where all these symptoms are affected are fatal within one week.