Radiation Therapy Principles

+ -Text Size


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. Since radiation is a local treatment, side effects depend on the area of the body being treated. 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. Other effects may not show up until months, or even years, later. The most common side effects are briefly discussed below. Please see our document called Understanding Radiation Therapy: A Guide for Patients and Families for more information and ideas on dealing with these and other radiation side effects.

For general information on managing the effects of cancer and its treatment (including chemotherapy as well as radiation), see Caring for the Patient With Cancer at Home: A Guide for Patients and Families.


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 (a low red blood cell count), poor nutrition, pain, certain drugs such as steroids or chemotherapy, depression, and stress.

There’s no single treatment for fatigue, but if a cause can be found it should be treated. For example, if the fatigue is caused by anemia, some patients may benefit from blood transfusions or from medicines that cause the body to make more red blood cells.

Fatigue can last for a long time after treatment is over and some people never have as much energy as they did before treatment. Light or moderate exercise with frequent rest breaks may help to reduce fatigue. Talk with your doctor about this and other treatments that might work for you.

You can learn more about fatigue and how to deal with it in our documents called Fatigue in People With Cancer and Anemia in People With Cancer.

Skin changes

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 (color). You could also lose hair in the skin over the area that is being treated.

The skin in the treatment area may also become dry and itchy. Moisturizing the skin with aloe vera, lanolin, or vitamin E may help. But before using any skin products during treatment, ask the radiation doctor or nurse if it’s OK. Some lotions that are safe to use after treatment ends can actually make things worse during treatment.

Do not use perfumes, deodorants, and skin lotions that contain alcohol or perfume on the treated area. Also avoid powders unless your doctor or nurse says they’re OK to use. Stay out of the sun as much as you can. If you must be outdoors, wear a hat and clothes that will protect your skin. After about a month of treatment, some people getting radiation may notice skin peeling and moist (weeping) areas. Let your medical care team know if this happens to you.

Later effects of radiation may include thinning of the skin. The skin may feel hard, especially if surgery has also been done in the same area. Some people may have trouble with wound healing in the area that was treated. The skin in the treatment area may always be more sensitive to the sun, and you should be extra careful to protect it when you are outdoors.

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. Thick, sticky, rope-like saliva and swallowing problems may develop, too. These side effects often go away after treatments end, but sometimes they don’t.

Keeping your mouth clean is important to lower your risk of infection. If your mouth becomes painful, you may be given medicine to numb the mouth or help the pain. You may need to take it before meals so that it’s easier to eat. Be sure to tell your doctor about any pain and if the medicines to help it are working.

Good nutrition is important for people with cancer. If mouth pain and irritation make it hard to eat or swallow, you may need to have a feeding tube put into your stomach for a while so you can take in enough nourishment. Your health care team will help you develop a plan to manage your symptoms. For more suggestions, see our document, Nutrition for the Person With Cancer During Treatment: A Guide for Patients and Families.

Radiation to the head and neck area can affect your teeth, too, and increase your chances of getting cavities. Mouth care to prevent problems will be an important part of your treatment. Before starting radiation, talk to your dentist and have a complete check-up. Also ask your dentist to talk to your radiation oncologist before your radiation treatments begin, and be sure to discuss your daily mouth care routine with the doctor or dentist. Any dental work you need may have to be done before radiation begins and daily fluoride treatments may be prescribed to help protect your teeth.

Last Medical Review: 10/23/2013
Last Revised: 10/23/2013