Radiation therapy, or radiotherapy, is a treatment that uses high doses of radiation to kill cancer cells and shrink tumors.

Though the radiation is targeted, it affects healthy cells as well as cancerous ones. For this reason, people undergoing radiation therapy (RT) can develop short- and long-term side effects during and after treatment.

This article describes common side effects of RT and provides tips for management and care.

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There are two types of RT: external beam radiation and internal radiation.

External beam radiation

This involves a machine sending beams of radiation to specific parts of the body.

The beams are lower-energy, and they intersect at the targeted areas, so that these receive higher doses of radiation. For this reason, cancer specialists, called oncologists, refer to the treatment as “localized.”

Internal radiation

Internal radiation kills cancer cells from inside the body.

This involves an oncologist either implanting solid radioactive material at the site of the tumor or giving the person liquid drugs made up of a radioactive substance. These can be taken orally or injected.

A solid source of radiation acts as a localized treatment. Radioactive beads, for example, are a common treatment for prostate cancer.

A liquid radiation source acts as a systemic treatment because it travels throughout the body.

RT effectively destroys cancer cells, but it also damages healthy cells. This can cause adverse effects during and after treatment. In some cases, a person may develop new side effects several months after the treatment ends.

The specific adverse effects can depend on the type of RT and the part of the body receiving the treatment.

Early side effects

According to the American Cancer Society, fatigue and skin changes are the most common early side effects of RT.

Examples of these skin changes include:

Other early side effects of RT can include:

Late side effects

These side effects can appear 6 months or longer after finishing RT and can include:

Before RT begins, a doctor will describe the adverse effects that a person may experience during and after the treatment.

If any side effects arise during treatment, inform the doctor as soon as possible — some effects indicate that the treatment program should be changed or that the person should be taking radioprotective drugs.

Other side effects may improve with lifestyle changes and home care. Below, we look at ways of managing some side effects of RT.


The following care strategies can help alleviate fatigue:

  • sleeping for at least 8 hours each night
  • taking short naps during the day
  • limiting strenuous, physically demanding tasks
  • asking friends and family members for help with daily tasks, such as cleaning and grocery shopping
  • performing a little light exercise each day
  • setting aside time for relaxing activities, such as yoga, meditation, and reading

Hair loss

To prevent hair loss, a person can try:

  • using hair products that are mild, such as baby shampoo
  • avoiding hairsprays, dyes, and other hair products that contain harsh chemicals
  • patting the hair dry with a towel, as opposed to rubbing the hair
  • avoiding hairdryers, flat irons, and curling irons

Skin changes

The following strategies can help a person care for sensitive or damaged skin:

  • refraining from rubbing or scratching the area
  • keeping the skin clean and dry
  • using gentle moisturizers or creams that repair the skin barrier
  • wearing soft fabrics
  • avoiding tight, restrictive clothing
  • wearing sunscreen, even on cloudy days

Mouth and throat changes

To manage mouth and throat pain or sensitivity, try:

  • avoiding foods that are hard, crunchy, spicy, or acidic
  • eating soft foods
  • cooking with sauces to help soften food
  • taking smaller bites
  • avoiding extremely hot foods and beverages
  • avoiding caffeinated beverages
  • drinking through a straw

Bowel and bladder changes

The strategies below can help with managing bowel and bladder issues resulting from RT:

  • drinking plenty of clear liquids each day to prevent dehydration and constipation
  • eating foods rich in potassium and sodium to maintain the body’s electrolyte balance
  • eating smaller meals throughout the day to improve digestion
  • eating yogurt, bananas, and other high-fiber foods to prevent diarrhea
  • avoiding hard-to-digest foods and beverages, such as dairy products, alcohol, and fried foods

RT damages DNA inside cells, which can lead to long-term side effects.

The specific effects may depend on the location and doses of RT. Some examples of long-term side effects include:


The thyroid is a small butterfly-shaped gland that sits in the front of the neck. It produces hormones that regulate numerous functions, including:

  • body temperature
  • heart rate
  • metabolism
  • bone growth
  • muscle function

RT to the head or neck can sometimes cause hypothyroidism — which refers to the thyroid not producing enough hormones.

Experts estimate that 19–45% of people develop hypothyroidism after undergoing RT for nose, throat, head, and neck cancers.

A 2018 study investigated thyroid changes in 56 people with nasopharyngeal carcinoma. On average, the participants’ thyroid glands shrank by as much as 39.8%, and their thyroid hormone levels decreased by 21.5% within 30 months of finishing RT.

After 36 months, however, the participants’ thyroids stopped shrinking, and their hormone levels stabilized.

Cognitive changes

A person who receives RT to treat a brain tumor may experience long-term cognitive changes, such as:

  • reduced processing speed
  • changes in attention and concentration
  • changes in verbal learning
  • decreased working memory
  • changes in executive functioning, which includes the ability to:
    • plan
    • think flexibly
    • exert self-control

Musculoskeletal problems

RT can weaken bones, leading to osteoporosis and an increased risk of fractures.

Radiation can also cause muscle cells to deteriorate, resulting in:

Secondary cancers

RT alters DNA inside cells, which can increase a person’s risk of developing cancer.

According to the American Cancer Society, previous exposure to radiation is a significant risk factor for most types of leukemia.

It is difficult to predict whether a person will develop secondary cancer after receiving RT. However, the following factors could increase the risk:

  • Age: Younger people who undergo RT may have a higher risk of developing a secondary tumor several years after completing the treatment.
  • Dose: The risk of developing cancer increases with higher doses of radiation.
  • Area of exposure: Certain organs are more susceptible to developing secondary cancer from RT, including the skin and breasts

RT involves exposure to radioactive materials. People who have undergone RT may need to take precautions to protect others from radiation exposure.

External beam RT involves a source of radiation outside of the body, which means that the person is not radioactive during or after the treatment.

However, if a person has received internal RT, radioactive particles can leave the body through sweat, blood, urine, semen, saliva, and other fluids.

People receiving internal RT as an oral capsule or injected liquid — called systemic RT — may need to stay in the hospital for 1 or 2 days afterward, until their body no longer gives off radiation.

Tips for protecting others

People undergoing systemic RT should take precautions to protect others from radiation exposure.

For at least the first few days after receiving systemic RT:

  • Try to maintain a 6-foot distance from other household members.
  • Particularly, try to avoid close contact with infants, children, pregnant women, and pets.
  • Avoid public transportation.
  • Avoid going to work, such as by working from home, if possible.
  • Wash clothing, towels, and bedding separately from those of other household members.
  • Do not share utensils or personal care items.
  • Wash the hands thoroughly after using the toilet.
  • Flush the toilet twice after each use.
  • Avoid intimate contact, usually for a minimum of 1 week.

RT is an effective cancer treatment, but it can lead to various short- and long-term side effects.

The most common side effects include fatigue, skin changes, and hair loss, but specific effects depend on the targeted area of the body and the dose of radiation.

An oncologist can provide more information about the risks and more likely adverse effects.

Notify the oncologist if any side effects develop. The doctor may need to change the treatment regimen or provide radioprotective drugs.