Over time, we have come to think of radiation in terms of its biological effect on living cells. In addition, the human body has defense mechanisms against many types of damage induced by radiation. Radiation may have one of three biological effects, with distinct outcomes for living cells:


  • Injured or damaged cells repair themselves, resulting in no residual damage;
  • Cells die, much like millions of body cells do every day, being replaced through normal biological processes;
  • Cells incorrectly repair themselves, resulting in a biophysical change.

Radiation therapy uses high-energy particles or waves to destroy or damage cancer cells. It is one of the most common treatments for cancer, either by itself or along with other forms of treatment. 

How does radiation therapy kill cancer cells?

Radiation therapy kills cancer cells by damaging their DNA. Radiation therapy can either damage DNA directly or create charged particles within the cells that can in turn damage the DNA.

Cancer cells whose DNA is damaged beyond repair stop dividing or die. When the damaged cells die, they are broken down and eliminated by the body’s natural processes.

Possible side effects of radiation therapy

Normal body tissues vary in their response to radiation. As with tumors, normal tissues in which cells are quickly dividing may be affected. This causes some of the side effects of radiation treatment. The early effects of radiation may be seen a few days or weeks after treatments have started and may go on for several weeks after treatments have ended.


Fatigue is an extreme tiredness that does not get better with rest. It’s a common effect of radiation, but the exact cause is unknown. Sometimes tumors cause the immune system to make substances that lead to fatigue. Fatigue may also be caused by anemia, poor nutrition, pain, certain drugs such as steroids or chemotherapy, depression, and stress.


Radiation therapy today causes less skin damage than it did in the past, but your skin might still show a response to treatments. During the first 2 weeks of treatment, you might notice a faint redness. Your skin may become tender or sensitive. A few people have blistering of the outer skin layer, with some weeping until it heals. Dryness and peeling may occur in 3 to 4 weeks. After that, the skin over the treatment area may become darker. This is because of the effect radiation has on the cells in the skin that produce pigment. You could also lose hair in the skin over the area that is being treated.

Mouth and throat problems

Mucositis, inflammation inside the mouth and throat, is a short-term side effect that can happen when radiation is given to the head and neck area. It can make swallowing painful, and some patients lose weight because they have trouble eating. It usually gets better within a few weeks after treatments end. Dry mouth and a loss of taste can be caused by radiation damage to the salivary glands and taste buds.

Radiation is one of the most common treatments of cancer, either by itself or along with other treatments. The human body has defense mechanisms against many types of damage induced by radiation. Most of the side effects are only temporarily and tend to fade away after treatment is complete.