Acute radiation syndrome (ARS), also known as radiation poisoning, radiation sickness or radiation toxicity, is a collection of health effects which present within 24 hours of exposure to high amounts of ionizing radiation. The radiation causes cellular degradation due to damage to DNA and other key molecular structures within the cells in various tissues; this destruction, particularly as it affects ability of cells to divide normally, in turn causes the symptoms. The symptoms can begin within one or two hours and may last for several months. The terms refer to acute medical problems rather than ones that develop after a prolonged period.
The onset and type of symptoms depends on the radiation exposure. Relatively smaller doses result in gastrointestinal effects such as nausea and vomiting and symptoms related to falling blood counts such as infection and bleeding. Relatively larger doses can result in neurological effects and rapid death. Treatment of acute radiation syndrome is generally supportive with blood transfusions and antibiotics, with some more exotic treatments such as bone marrow transfusions being required in extreme cases.
Similar symptoms may appear months to years after exposure as chronic radiation syndrome when the dose rate is too low to cause the acute form. Radiation exposure can also increase the probability of developing some other diseases, mainly different types of cancers. These diseases are sometimes referred to as radiation sickness, but they are never included in the term acute radiation syndrome.