How radiation affects cells

The primary way radiation affects our health is through breakage of DNA molecules. DNA is a long chain of amino acids whose pattern forms the blueprint on how the cell lives and functions.  Radiation is able to break that chain. When it does,  three things can happen:  

1) The DNA is repaired properly

In this case, the cell is repaired properly and it continues to function normally. DNA breakage occurs normally every second of the day and cells have a natural ability to repair that damage.

2) The DNA damage is so severe that the cell dies (deterministic effects)

When the DNA or other critical parts of a cell receive a large dose of radiation, the cell may either die or be damaged beyond repair. If this happens to a large number of cells in a tissue or organ, early radiation effects may occur. These are called deterministic effects and the severity of the effects varies according to the radiation dose received. They can include burns, cataracts, and in extreme cases, death.

The first evidence of deterministic effects became apparent with early experimenters and users of radiation. They suffered severe skin and hand damage due to excessive radiation dose. More recently, this relationship was observed at the 1986 Chernobyl nuclear plant accident where more than 130 workers and firefighters received high radiation doses (800 to 16,000 mSv), and suffered severe radiation sickness. Two of the people exposed died within days of exposure. Close to 30 more workers and firefighters died within the first three months.

The CNSC and other international regulators put measures in place, including stringent dose limits and radioactive source tracking databases, to mitigate the chances of the public or workers receiving doses of radiation high enough to cause deterministic effects. The CNSC also has strict regulations on how nuclear substances and devices must be handled in Canada. 
3) The cell incorrectly repairs itself, but it continues to live (stochastic effects)

In some cases, the DNA of the cell may be damaged by radiation, but the damage does not kill the cell.  The cell may continue to live and even reproduce itself, but the cell and its descendents may no longer function properly and may disrupt the function of other cells.  The probability of this type of  detrimental effect is proportionate to the dose and it is called a stochastic effect – when there is a statistical probability that the effects of exposure will occur. In such cases, the likelihood of the effects increases as the dose increases. However, the timing of the effects or their severity does not depend on the dose. 

This process happens all the time in everyone. In fact, people are exposed to about 15,000 such events every second of every day. Sometimes, the cell structure changes because it repairs itself improperly. This alteration could have no further effect, or the effect could show up later in life. Cancer and hereditary effects may or may not take place.