“Radiation poisoning” is the common term for Acute Radiation Syndrome (ARS), a severe illness resulting from whole-body exposure to a high dose of penetrating ionizing radiation over a short period, typically minutes. For ARS to occur, the absorbed radiation dose must generally be greater than 0.7 Gray (Gy), delivered rapidly enough to cause systemic damage. The syndrome is not contagious; an exposed person who has been decontaminated poses no radiation risk to others. This condition primarily affects the body’s most rapidly dividing cells, such as those in the bone marrow and the lining of the gastrointestinal tract, leading to a predictable pattern of systemic breakdown.
Initial Warning Signs
The prodromal stage is the initial response to high-dose radiation, beginning within minutes to hours after exposure. This phase is characterized by non-specific, transient symptoms whose severity and speed of onset relate directly to the absorbed dose. Individuals commonly experience acute nausea, vomiting, diarrhea, general fatigue, headaches, and loss of appetite (anorexia).
For very high doses, these symptoms appear within minutes, while lower doses may delay onset by several hours. This initial sickness is intense but brief, lasting from minutes up to a couple of days, before lessening or disappearing, which can create a false sense of recovery.
The Progression of Illness
The course of Acute Radiation Syndrome begins with the Prodromal Phase and moves into the Latent Period. Following the initial nausea and vomiting, the patient enters the Latent Period, where they appear and feel relatively well, often with few or no visible symptoms. This apparent improvement can last from a few hours to several weeks, with the duration inversely proportional to the initial radiation dose.
During this latent phase, significant damage is silently progressing at the cellular level, particularly in rapidly dividing stem cells of the bone marrow and gastrointestinal tract. A shorter latent period is a critical indicator of a higher and more lethal exposure. Once damaged cells can no longer be replaced, the illness progresses into the Manifest Illness stage, where severe, life-threatening symptoms associated with systemic organ failure become visible.
Organ System Failure by Severity
The clinical appearance of the manifest illness stage is defined by three dose-dependent syndromes, each targeting different organ systems due to their varying cell turnover rates.
Hematopoietic Syndrome
The Hematopoietic Syndrome, or Bone Marrow Syndrome, occurs at moderate whole-body doses, generally between 0.7 and 10 Gy. This syndrome destroys the bone marrow’s stem cells, which are responsible for producing all blood cells. Failure to produce white blood cells leads to severe susceptibility to infection, often presenting as persistent fever and generalized weakness.
The lack of platelets, which are necessary for clotting, results in hemorrhage, including easy bruising, petechiae—tiny purple, red, or brown spots on the skin—and prolonged bleeding from minor injuries. Damage also reduces red blood cell production, contributing to anemia and fatigue. The primary causes of death are overwhelming infection and uncontrolled internal bleeding.
Gastrointestinal Syndrome
Higher doses of radiation, typically above 6 to 10 Gy, trigger the Gastrointestinal (GI) Syndrome. This exposure severely damages the lining of the small intestine, destroying the crypt cells that replenish the mucosal barrier. Destruction of this lining causes sloughing of the intestinal wall, leading to severe, relentless, and often bloody diarrhea.
The loss of the protective barrier results in an inability to absorb fluids and nutrients, causing rapid dehydration and electrolyte imbalance. Bacteria from the gut can pass into the bloodstream through the damaged wall, causing sepsis and systemic infection. This breakdown, compounded by circulatory collapse, leads to death often occurring within two weeks.
Cerebrovascular/CNS Syndrome
The most severe form is the Cerebrovascular or Central Nervous System (CNS) Syndrome, seen at extremely high doses, typically above 20 to 50 Gy. Acute damage to the circulatory system and brain tissue causes immediate neurological collapse. Symptoms begin almost immediately after exposure and include nervousness, confusion, and a loss of coordination called ataxia.
The radiation causes blood vessels in the brain to swell, leading to increased pressure within the skull, which manifests as severe vomiting, disorientation, and seizures. The rapid progression of vasculitis and edema leads to a quick deterioration of mental status, coma, and ultimately, death, often within one to three days of exposure.