Radiation sickness occurs after exposure to ionizing radiation. The disease is a manifestation of acute radiation damage to cells, which causes their death (necrosis). It is important to emphasize that radiation is dangerous especially for those tissues, whose cells proliferate faster and vice versa. This is, of course, the main mechanism of radiotherapy in cancers as cancer cells tend to multiply very quickly. The body tissues most sensitive to radiation are male gonads (sperm production), bone marrow (blood cells production), skin (permanent renewal of skin cover) and digestive tract (quickly resurfacing mucous membranes). On the contrary, the brain is an organ very resistant to irradiation, because its cells practically do not multiply.
Direct cell damaging effect of radiation can be accurately determined and predicted. That means we know what radiation energy leads to certain symptoms. The energy can be measured in many physical units; usually we talk about the Sieverts [Sv] and milliSieverts [mSv]. The Sievert expresses the dose of received energy and its effect on various tissues. In a development of radiation sickness, it is essential that the body has been affected by certain amount of Sieverts in a very short time period.
Before we discuss the basic symptoms, it is advisable to compare some situations that are related to excessive radiation exposure.
Abdominal computed tomography: 5-15 mSv per examination
Fixed dose for employees working with radiation: an average of 20 mSv per year for 5 years (i.e. totally 100 mSv in 5 years) with a maximum annual dose of 50 mSv
Workers at Fukushima nuclear plant after the accident: around 200mSv in few days
There are usually no acute symptoms. This dose refers to the staff of the Japanese nuclear power plant Fukushima during the days of the accident.
There may appear mild symptoms such as nausea and loss of appetite. Men may suffer from a temporary infertility caused by damage done to sperm cells being produced at the time of the exposure.
There are nausea and loss of appetite. In blood count, we may find slightly reduced number of white blood cells. The symptoms appear in several hours after the exposure.
The nausea occurs more frequently and it is often accompanied by vomiting. The victim suffers from headache and elevated temperature. The number of white blood cells is significantly decreased. The immune system is weakened and the affected person may suffer from recurring infections. The hair may fall out and the skin cover may be damaged. Disrupted blood coagulation results in bleeding from mucous membranes and sometimes even internal bleeding.
There are strong symptoms such as nausea, vomiting, diarrhea, decreased white blood cell count and hair loss. Severe diarrhea due to intestinal damage by radiation colitis can cause disruption of the internal environment of the organism.
The above mentioned symptoms are accompanied with impaired consciousness. The death is virtually certain. Severe skin damage causes occurrence of large-scale radiation burns.