Health effects of radiation
Units of measurement:
Gray (Gy)
Unit of an absorbed dose, indicating how much energy the ionizing radiation gives out to the target substance. 1 Gy = 1 J/kg.
Sievert (Sv)
A unit of radiation dose indicating the health detriments caused by radiation.
Ionizing radiation can damage the DNA of living cells. In terms of cell damage, what is significant is whether the radiation dose is received over a short or long period. Even a small radiation dose may slightly increase the risk of cancer. A high radiation dose received over a short period of time can cause radiation sickness, tissue damage or foetal damage.
Radiation absorbed into living tissue launches physical and chemical reactions that may cause biological changes. Electrons detached by radiation create reaction products that may cause genetic damage, i.e. damage to the DNA. In addition to DNA damage, other effects, known as epigenetic effects, can also transfer to cells and tissue outside the area exposed to radiation.
Health detriments largely caused by radiation are the result of damages to the DNA molecule. Some of the DNA damage will be repaired and not all DNA damage leads to a health detriment. Radiation can leave a permanent change called a mutation in the DNA. The accumulation of several mutations can lead to the development of cancer. The development of cancer is a long and complicated process and it is affected by other factors in addition to radiation.
Leukaemia and thyroid cancer in children may appear as early as two years after the exposure. The emergence of other types of cancer may take more than 10 years.
Information about the cancer risk has been obtained from studies of people exposed to radiation in various contexts. Some of the most significant studied people include the survivors of the Hiroshima and Nagasaki atomic bombings, those exposed to radiation due to its use in medical treatment and those exposed to radiation in their work.
In practice, the risk of cancer caused by low doses of radiation cannot be detected in the general population, as cancer is so common and the effect of low doses of radiation disappears due to variation in cancer risk caused by other factors (statistical “noise”). In Finland, the occurrence of different types of cancer has been monitored by the Finnish Cancer Registry since 1953. About 35,000 people are diagnosed with cancer every year in Finland (Finnish Cancer Registry 2023). For instance, according to estimates, the Chernobyl fallout, resulting in the average total dose of 2 millisieverts (mSv) to a Finn over an 80-year period, may cause some tens or hundreds of cancer cases in Finland during that period. At the same time, however, about one million people will be diagnosed with cancer for other reasons, which makes the estimate on the effects of the Chernobyl accident merely computational.
If a person is exposed to a small dose of radiation in, for instance, their work and is later diagnosed with cancer, it is very unlikely that the radiation exposure from work is the reason for the cancer.
Exposing the skin to large quantities of UV radiation and getting sunburn increases the risk of skin cancer.
Further information on UV radiation
Approximately two thirds of the annual radiation dose received by Finns results from radon in indoor air. Long-term exposure to high radon levels increases the risk of lung cancer. Radon exposure is estimated to cause 150-270 cases of lung cancer each year in Finland. The radiation dose received into the lungs increases the risk of lung cancer. The longer the stay and the higher the radon level, the higher the risk.
Radiation sickness is developed if a body is exposed to an extremely large (over one sievert, i.e. 1,000 millisieverts) dose of radiation over a short time. The mortality rate among those who are exposed to a radiation dose of 8 sieverts over a short time is very high. Radiation sickness is due to extensive destruction of the cells. Organs with a large number of dividing cells are the most vulnerable to radiation, such as bone marrow and the intestines.
Radiation exposure to even a high dose cannot be immediately detected, as humans do not have a sense that recognizes radiation. The first symptom of radiation sickness is nausea, which begins within a couple of hours. The actual radiation sickness does not fully develop until after a couple of weeks. One of the main symptoms is the paralysis of bone marrow. The numbers of all the blood cells drop, resulting in infections and bleeding. The mucous membrane of the intestines is also damaged, which causes diarrhoea. Radiation sickness may lead to death in about one month. The prognosis can be improved with high-quality treatment.
Radiation doses leading to local tissue damage, radiation sickness or death have occurred in situations where ordinary members of the public have unknowingly handled potent sources of radiation manufactured for industrial or medical use. However, this has never happened in Finland.
During pregnancy, unnecessary radiation exposure must be avoided as radiation exposure during the foetal period increases the child's risk of getting cancer. Low doses of radiation (<50 mGy) have not been shown to affect the risk of malformations.
In the sensitive stage of foetal development, i.e. early pregnancy (during the 2nd to 8th week of pregnancy), a higher dose of radiation can cause disturbances in foetal growth and nervous system development. Other developmental impacts have only been detected after extremely large doses (several grays).
Radiation exposure at a very early stage, before the mother is even aware of the pregnancy, may cause an early miscarriage. If, however, the pregnancy continues and the foetus is not exposed to radiation in the future, the child is likely to be born healthy.
Holding a potent source of radiation can create a severe radiation damage in a very short time. However, the damage does not appear immediately. On the first day, the damaged skin area is red. After a couple of weeks, the skin may form blisters. The treatment of radiation damage is difficult and time-consuming. The exposed area may become gangrenous even after an entire year as its bloodstream has been destroyed. Tissue exposed to radiation also often accumulates connective tissue, which can impair the functioning of the body in many ways.
High doses of radiation used in radiotherapy can increase the occurrence of cardiovascular diseases. Recent studies have also shown that lower doses of radiation may increase the risk of diseases of the cardiovascular system. So far, however, the scientific evidence is not uneqivocal or indisputable. UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation) is preparing a scientific estimate on the effects of small doses of radiation on cardiovascular diseases.
Several studies report that the opacities at the back of the lens of the eye is more common in groups working with radiation. Opacities in the lens of the eye, i.e. cataracts, have been observed in employees cleaning the Chernobyl accident site. It is suspected that exposure to radiation may have an effect on the occurrence of a cataract. People carrying out medical procedures, such as interventional cardiologists and interventional radiologists, are exposed to radiation in their work. The lens of the eye is also often exposed to radiation, which may lead to the formation of cataracts if the dose is large enough. The dose directed at the lens can be effectively reduced by wearing protective goggles or other safety gear. However, a Finnish study showed that physicians exposed to radiation in their work are not at a greater risk of developing clouding than other physicians. The difference to studies reported from other countries may be due to the fact that the committed dose in the Finnish study was significantly smaller.