Gamma rays are dangerous because they cause cellular damage that leads to DNA damage, cancer and radiation sickness. Because gamma rays are such a high-intensity, ionizing form of radiation, they pass through normal protections, such as skin, clothing, foil and goggles. Only high-mass shielding, such as lead, can stop them.
Radioactive decay, lightning strikes and nuclear explosions emit gamma rays. They also occur during medical procedures, such as X-rays and radiation therapy. During radiation treatment for cancer, radioactive isotopes emit gamma rays in a controlled area to arrest the development of cancerous tumors. However, overexposure to gamma-ray-producing radiation from X-rays, particle accelerators, nuclear reactors or nuclear weapons causes radiation sickness, also known as acute radiation syndrome.
The amount and duration of exposure to radiation determines the rapidity of radiation sickness onset and its symptoms. Exposure to high amounts of gamma radiation can result in the rapid development of extreme symptoms, followed by death, whereas steady exposure to lower amounts of ionizing radiation can delay symptoms for months. Hematopoietic syndrome is characterized by a loss of blood cells, which complicates healing of conventional wounds after traumas, such as bomb blasts. Gastrointestinal syndrome causes symptoms, such as nausea, vomiting, abdominal pain and appetite loss, and is often followed by death. Neurovascular syndrome is always fatal and occurs rapidly, causing headaches, dizziness and lack of awareness of surroundings. Even when gamma-ray-producing radiation is too low to induce fatality, it can lead to radiation-induced cancer.