What we know about severe radiation sickness comes from a relatively small number of accidents involving radioactive materials, as well as the victims of the Hiroshima and Nagasaki atomic bomb attacks.
At 5 Sv and up, radiation can damage skin so severely that it doesn't heal properly. Hair falls out. Scars develop beneath the skin will that swell and form keloids. Unfortunately, some scientists know the horrors of radiation exposure firsthand. For instance, physicist Harry K. Daghlian, Jr. suffered a 5.1 Sv exposure in 1945 while working on a plutonium core. He suffered severe burns to his hands and died 25 days after the accident [source: Los Alamos National Laboratory]. Another physicist, Louis Slotin, suffered a similar accident -- using the exact same core -- just one year later. Slotin was exposed to a 21 Sv dose, which is a massive amount of radiation. He vomited immediately, and then suffered through nine days of horrific symptoms before dying. The incident that killed Slotin was so intense that the air in the lab itself became ionized, causing a clear blue glow and a visible wave of heat [source: Los Alamos National Laboratory]. His symptoms were very similar to those seen in victims of the atomic bomb attacks on the Japanese cities of Hiroshima and Nagasaki.
Once you're exposed, how are you treated? Radiation sickness treatment starts with decontaminating the patient if any radioactive material is still present. External decontamination involves washing, while internal exposure (from inhalation or ingestion) requires the use of special drugs, such as Prussian blue dye or diethylenetriamine pentaacetic acid, which binds to radioactive particles and flushes them from the body [source: Mayo Clinic]. Symptoms can be treated individually to ease the patient's suffering. Antibiotics are used to fight or prevent infections, since the immune system is so weakened by bone marrow damage. If the marrow is only slightly damaged, blood transfusions can increase the chance of survival. If damage is severe, a bone marrow transplant may offer some hope.
The best way to prevent radiation sickness, of course, is to avoid intense sources of radiation. The most common way for people to become exposed to a radioactive source is by encountering improperly disposed of radioactive materials that were used in industry or medicine. For example, in 1987, scavengers found a radiation source used for radiation therapy in an abandoned hospital in Goiânia, Brazil. Finding the glowing blue caesium inside decorative, the scavengers sold it, exposing dozens of people to gamma radiation. Four people eventually died of radiation sickness [source: Time].
Incidents like the nuclear reactor problems following the Japanese earthquake and tsunami in 2011, as well as the potential for terrorist attacks using nuclear or radioactive devices has pushed the U.S. to seek more effective pharmaceutical treatments for radiation sickness. Researchers are working on a drug that would protect cells from radiation damage and even repair already damaged cells [source: VOANews].
Hopefully, most of us will never have to use it.