Health effects of radiation

Ionizing radiation can damage the DNA of living cells. In terms of cell damage, whether the radiation is natural or man-made is irrelevant. However, what is significant is whether the radiation dose is received over a short or long period. Even a small radiation dose slightly increases the risk of cancer. A high radiation dose received over a short period of time can destroy a large number of cells and cause radiation sickness, local injury or foetal damage.

Radiation absorbed into living tissue launches physical and chemical reactions that cause biological changes. Radiation dismantles some of the DNA chains in our cells. This may damage and, typically, break the structure of the DNA. Electrons detached by radiation create reaction products that damage the DNA. DNA is not the only part affected by radiation. Other effects, known as epigenetic effects, can also transfer to cells and tissue outside the area exposed to radiation. Extensive or strong radiation exposure can lead to local destruction of cells or radiation sickness. Non-lethal effects to the cells may later result in other health detriments.

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.

Radiation and cancer

Health detriments caused by radiation are the result of damages to the DNA molecule. However, not all DNA damage leads to a health detriment. Radiation can leave a permanent change called a mutation in the DNA. When several mutations accumulate, the result may be a cancerous tumour. The journey to a final detriment is long and complicated and can be affected by other factors in addition to radiation. Leukaemia and thyroid cancer in children may appear as early as two to five years after the exposure. The emergence of other types of cancer may take more than 10 years.
Estimates regarding the risk of cancer are primarily based on cohort studies on three groups exposed to radiation. These groups consist of 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.

There are no practical means of detecting a risk of cancer caused by small doses of radiation in the population as cancer is a very common disease. New occurrences of cancer in Finland have been monitored by the Finnish Cancer Registry since 1953. About 32,000 people are diagnosed with cancer every year in Finland. The potential small addition caused by radiation is statistically obscured by natural variability. For instance, according to estimates, the Chernobyl fallout, resulting within a timespan of 80 years in the average total dose of 2 millisieverts (mSv) to a Finnish person, may cause some cancer-related deaths in Finland. At the same time, however, about one million people will die of cancer for other reasons, which makes the estimate on the effects of the Chernobyl accident merely computational.

If a person is exposed to 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.

Sievert (Sv)

A unit of radiation dose indicating the health detriments caused by radiation.

Radiation sickness

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. If a person is exposed to a radiation dose of 8 sieverts over a short time, death is almost certain. Radiation sickness is due to extensive destruction of the cells. Organs with a large number of dividing cells are the most vulnerable to radiation.

A person will not perceive anything immediately after the exposure, as radiation cannot be sensed. The first symptom 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 bone marrow failure. 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.

Radiation doses leading to local injury, radiation sickness or death have occurred in situations where ordinary citizens have unknowingly handled potent sources of radiation manufactured for industrial or medical use. However, this has never happened in Finland.

Impacts on foetus

During pregnancy, unnecessary radiation exposure must be avoided as radiation exposure during the fetal period increases the child's risk of getting cancer. Small radiation doses do not increase the number of malformations.
Exposing a foetus to a large, sudden dose of radiation at a vulnerable age may lead to reductions in the size of the head and the body, as well as mental retardation. Other developmental impacts have only been detected after extremely large doses (several grays). A foetus may be exposed to such doses of radiation if the mother receives radiation therapy during the pregnancy.

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, the child is likely to be born healthy.

Local injury

Holding a potent source of radiation can create a severe local injury in a very short time. However, the injury does not appear immediately. On the first day, the burned skin only turns red. After a couple of weeks, the skin may form blisters. The treatment of radiation injuries is difficult and time-consuming. The skin may become gangrenous even after an entire year as its bloodstream has been destroyed.

Cardiovascular diseases

A large dose of radiation may cause enough injuries to increase the occurrence of cardiovascular diseases. This has been observed in young patients, whose cancer treatment has made high levels of radiation targeted at the heart's blood vessels unavoidable. The effects of small doses are examined in both epidemiologic and laboratory studies. So far, however, the scientific evidence is not univocal 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. The report will likely be completed in 2018.


Cataract has been observed in employees cleaning the Chernobyl accident site. It is suspected that exposure to radiation may have an effect on the occurrence of cataract. This has also been observed in interventional radiology. 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. The dose directed at the lens can be effectively reduced by wearing protective goggles or other safety gear. Several studies report that the clouding of the lens is more common in groups working with radiation. 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 accumulated dose in the Finnish study was significantly smaller. An extensive European collaborative study is currently underway to research the occurrence of lens clouding among intervention cardiologists. The study evaluates how the amount of radiation affects the development of clouding.

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  • Eeva Salminen / Research Professor