Radiation is a known carcinogen, and appears in two main forms with respect to cancer: ionizing radiation and ultraviolet radiation.

Ionizing radiation is caused by any particle or wave that has enough energy to remove electrons from an atom. Therefore ionizing radiation is very powerful and occurs at very high energies. Ionizing radiation comes in two forms: x-rays and gamma rays. Both are carcinogenic to humans.

X rays are 0.01 to 10nm long (1E-11 to 1E-8m long) and are invisible to the human eye. They are widely used in medical imaging and for security purposes.

Gamma rays are electromagnetic radiation of extremely high frequency and energy, even higher than x-rays. They can be produced naturally from radioisotopes and secondary radiation from atmospheric interaction. They are also produced during nuclear fission in nuclear explosions, such as atomic bombs. They are able to penetrate the body, and have the potential to disrupt function at a cellular level.


Knowledge on radiation risk has been mainly acquired from epidemiological studies of the Japanese A-bomb survivors as well as from studies of medical and occupational radiation exposure cohorts. Ionizing radiation can increase risk of developing leukaemia and a number of solid tumours, with higher risks for those exposed at younger ages. Ionizing radiation is an essential diagnostic and therapeutic tool. To guarantee that benefits exceed potential radiation risks radiological medical procedures should be appropriately prescribed and properly performed, to reduce unnecessary radiation doses, particularly in children1.

Another main risk of ionizing radiation is through residential exposure to radon gas from soil and building materials. It is estimated that between 3% and 14% of all lung cancers are due to radon exposure, making it the second most common cause of lung cancer after tobacco smoke. In Canada, about 3000 lung cancer deaths are related to radon each year2. Radon levels in homes can be reduced by improving the ventilation and sealing floors and walls

It is important to note that risk of cancer increases in a dose-response manner, such that increasing doses of radiation increases risk of developing cancer. Therefore, frequent and high doses of radiation are more likely to cause cancer than infrequent and low doses of radiation. The shape of this curve is linear at low, medium and high doses, but there is some controversy concerning the dose-response pattern at extremely low doses. Regardless, exposure to radiation should be avoided when consequences of exposure outweigh benefits.

Ultraviolet (UV) radiation, and in particular solar radiation, is carcinogenic to humans, causing all major types of skin cancer, such as basal cell carcinoma (BCC), squamous cell carcinoma (SCC) and melanoma. Globally in 2000, over 200 000 cases of melanoma were diagnosed and there were 65 000 melanoma-associated deaths. Avoiding excessive exposure, use of sunscreen and protective clothing are effective preventive measures. UV-emitting tanning devices are now also classified as carcinogenic to humans based on their association with skin and ocular melanoma cancers.

UV radiation can also cause premature skin aging, cataracts and certain eye cancers, such as choroid and ciliary body melanoma3.


1. World Health Organization. (2012). Cancer Prevention. Retrieved July 2015 from http://www.who.int/cancer/prevention/en/

2. Canadian Cancer Society. (2015). Radon. Retrieved July 2015 from http://www.cancer.ca/en/prevention-and-screening/be-aware/harmful-substances-and-environmental-risks/radon/?region=on

3. Canadian Cancer Society. (2015). Risk factors for eye cancer. Retrieved July 2015 from http://www.cancer.ca/en/cancer-information/cancer-type/eye/risks/?region=on