High doses of radiation cause acute radiation syndrome (ARS) because they inflict severe and rapid damage to the body’s cells and tissues, overwhelming the body’s ability to repair itself and maintain vital functions. When the body is exposed to a large amount of ionizing radiation in a short period, it disrupts the normal function of critical organs and systems, leading to a cascade of harmful effects that manifest as ARS.
Radiation primarily harms living cells by damaging their DNA and other cellular components. At low doses, cells can often repair this damage, but at high doses, the damage is too extensive and widespread. This leads to cell death or malfunction, especially in tissues with rapidly dividing cells such as the bone marrow, gastrointestinal tract, and skin. The loss of these cells impairs the body’s ability to produce blood cells, absorb nutrients, and protect against infections.
The severity of ARS depends on the radiation dose and the parts of the body exposed. For example, doses above 1-2 Gray (Gy) can cause symptoms like nausea and vomiting within hours, while doses in the range of 2.5-5 Gy can lead to more severe symptoms such as diarrhea, fever, and hair loss over days to weeks. At doses above 6 Gy, the damage becomes life-threatening, often resulting in death without intensive medical care.
One of the first systems affected is the bone marrow, which produces blood cells essential for oxygen transport, immunity, and clotting. Radiation destroys these marrow cells, causing a drop in red blood cells, white blood cells, and platelets. This leads to anemia, increased risk of infections, and bleeding problems. The gastrointestinal tract lining is also highly sensitive; radiation damages the cells lining the intestines, causing nausea, vomiting, diarrhea, and severe fluid loss. This damage can prevent nutrient absorption and lead to life-threatening infections as the gut barrier breaks down.
At extremely high doses (above 20-30 Gy), radiation affects the central nervous system and cardiovascular system. This causes neurological symptoms such as confusion, loss of consciousness, seizures, and rapid death due to brain swelling and circulatory collapse. These effects occur quickly because radiation damages the blood vessels and brain tissue, disrupting blood flow and increasing pressure inside the skull.
Radiation also causes inflammation and damage to blood vessels, leading to swelling, bleeding, and impaired circulation. This vascular damage contributes to the rapid progression of symptoms in the most severe forms of ARS. Skin exposed to high doses may develop radiation burns, starting with redness and itching, progressing to blistering, ulceration, and long-term scarring or cancer risk.
The progression of ARS typically follows stages: an initial prodromal phase with nausea and vomiting, a latent phase where symptoms temporarily improve, and then a manifest illness phase where severe symptoms develop depending on the dose and organs affected. Without prompt and specialized medical treatment, including supportive care and sometimes bone marrow transplantation, survival chances decrease sharply with increasing dose.
In essence, high doses of radiation cause acute radiation syndrome because they overwhelm the body’s cellular repair mechanisms, destroy critical tissues responsible for blood production and digestion, and disrupt vital organ systems, leading to a rapid decline in health and often death. The damage is systemic and multifaceted, involving direct DNA injury, cell death, inflammation, vascular damage, and immune system collapse, all of which combine to produce the complex and severe clinical picture of ARS.