Radiation therapy side effects and how to manage them

This page was reviewed under our medical and editorial policy by

Sean Cavanaugh, MD, Chair, Department of Radiation Oncology

This page was updated on September 24, 2021.

For cancer, doctors may recommend radiation therapy, a treatment that attacks cancer cells using high-energy sources such as electron beams, gamma rays or X-rays. It’s regularly used for both early-stage and advanced-stage cancers and often performed in conjunction with other cancer treatments.

Why does radiation cause side effects?

Radiation therapy is mainly confined to the cancerous tumor—or targeted areas of treatment—and not the surrounding areas. Still, radiation therapy uses high levels of radioactivity to fight cancer cells that may also damage nearby healthy cells and tissues. This may trigger troublesome reactions—some short-term and some long-lasting.

Patients should have frequent, consistent and open dialogue with their cancer care team about side effects before, during and after treatment. This is critical for receiving the appropriate recommendations for side effects management. 

How long will side effects from radiation last?

The side effects of radiation therapy may depend on the dose and length of treatment. Most patients' side effects subside within a few months post-treatment, but no two people are the same. The American Cancer Society (ACS) has developed a six-week external radiation therapy side effects worksheet to help patients track symptoms. The side effects of radiation therapy are sometimes difficult to identify, since they may be subtle in the early days of treatment. That's why it's important to discuss any questions or concerns with the radiation oncologist or nurse as soon as they occur.

Some side effects may not show up for months or years after completion of treatment, depending on dosage and type of treatment. When discussing follow-up care, patients should ask about any possible late side effects.

What are the side effects of radiation therapy?

A few main side effects are common with radiation therapy. Most symptoms, like hair loss, are only experienced in the area of the body being irradiated. Others, like fatigue, occur regardless of the area being treated. Knowing as much as possible about the different side effects and what to expect may help patients feel more in control and at ease.


Cancer fatigue is different from physical weakness. Cancer fatigue feels more like how people feel after a long day, only it's caused by the treatment. Also, the level of fatigue differs in each person. The larger the area being treated, the more fatigue the patient generally feels.

To manage fatigue, patients should take the steps listed below.

Balance rest and activity. Carve out time each day to find time to relax vs. time to do light activities, such as taking a walk or gardening.

Create a nutrition plan. Make sure to have plenty of water and a balanced diet of protein, carbs, fat, vitamins and minerals to keep energy levels up.

Find mental health support. Speaking with a counselor or psychologist may help to manage fatigue or mental health concerns often associated with cancer treatment.

Skin irritation and burns

Radiation therapy may cause dry skin, itchiness and, sometimes, radiation burns. In other cases, the skin may become sensitive to sunlight and become red.

To manage skin irritation, patients should consider the options below.

Use the medication prescribed. A cream or ointment may be recommended for skin swelling or dryness, but it should only be used as directed. In more severe cases, a patient may be prescribed an antihistamine or steroid.

Clean appropriately. Use warm water to rinse skin, then pat it dry with a towel. Avoid using a washcloth or sponges, which may cause further irritation.

Moisturize often. Lather the irritated areas of the skin with cream or thicker lotion to add moisture, but don’t use moisturizer on a wound.

Nausea and vomiting

Radiation therapy may make the patient feel queasy and lightheaded, and in rare cases, it may cause vomiting.

To manage nausea, patients should take the steps below.

Start with small meals. Try eating bland foods and drinking clear liquids. Instead of fewer, larger meals, “graze” and choose more mini-sized meals.

Set aside time for relaxation. Focus on mindful exercises, such as meditation, acupressure or acupuncture.

Stay connected to the care team. Don't hesitate to reach out to the care team with any questions or after experiencing any changes in appetite or nausea.

Hair loss (alopecia)

Some radiation treatments may cause hair loss or thinning in the area of the body being treated. This may include hair throughout the body, not only on the head.  

To manage hair loss, consider the options listed below.

Visit a hairstylist. Consider cutting or shaving off hair before it starts to fall out.

Wear a head covering. Some people buy wigs or wear scarves. Find out whether a wig would be covered by insurance. The ACS has a program called Tender Loving Care that helps patients evaluate wigs, hats and scarves.  

Be gentle with hair care. Don’t brush too often or pull too hard or use blow dryers and curling irons. Avoid perms and dyes, especially when hair starts to grow back.


During radiation treatment, specifically to the abdomen or pelvis, patients may experience diarrhea, or loose stools.

To manage diarrhea, take the steps below.

Contact the care team. If diarrhea develops, alert the care team right away.

Hydrate. Drink plenty of water and electrolytes to replenish and prevent dehydration. If this side effect continues, doctors may prescribe diarrhea medication.

Eat small, specific meals. Aim for smaller meals throughout the day, so the body isn’t working harder to digest larger meals. Try to include foods high in minerals such as potassium and sodium.

Sexual issues

These may occur if radiation therapy involves the pelvic area or sexual organs.

Women: If treatment is directed to the pelvic area, women may experience damage to delicate tissue in and around the genitals. This may cause irritation and tenderness. Radiation may also damage the lining of the vagina and lead to light bleeding after sex. To prevent that damage from resulting in scarring (fibrosis), the care team may recommend exercises or therapies to soften irritated tissue, such as stretching the walls of the vagina, which is performed by using a vaginal dilator or with vaginal penetration during sex.

Men: Radiation treatment in the pelvic area, including the anus, bladder, penis or prostate, may potentially damage blood vessels or nerves, making it difficult to keep an erection. It's safe for most men to try to be sexually active during and after treatment. Men experiencing these side effects should notify their care team. There are specific medications, both in pill form and as an injection, that may be prescribed to increase blood flow to the penis. If those therapies don't provide relief, some men may be a candidate for a surgical penile implant procedure that can assist in keeping an erection.

Fertility challenges

Women: If treatment is directed to the pelvic area, women may stop having menstrual periods or develop symptoms of menopause. Menstrual periods often return after treatment, but sometimes they don’t. Before undergoing treatment, women should speak with their care team about possible fertility issues.

Men: If treatment is directed to an area on or around the testicles, radiation may reduce sperm count. Men who undergo radiation therapy to the prostate may experience changes in semen, which may result in infertility. Men who want to bank sperm ahead of time should discuss this with their care team before treatment.

Urinary and bladder changes

Radiation therapy directed to the pelvic area may also cause urination or bladder issues, including pain or burning sensations while urinating, trouble passing urine, blood in the urine, or an urge to urinate often.

More severe, long-term side effects may occasionally include:

  • Radiation cystitis (damage to the lining of the bladder)
  • Urinary incontinence (loss of bladder control)
  • Fistulas (small openings between the organs in the pelvis)

Depending on the side effect, many options for management are available, including surgery to improve incontinence, medications, dietary changes and pelvic floor muscle strengthening.

Side effects in specific areas

Radiation is a localized therapy, so side effects typically differ depending on the part of the body being treated. Below, find a few more side effects of radiation, specific to the area of treatment.

Side effects of radiation therapy for brain cancer

After radiation therapy of the brain, patients may experience headaches or trouble with memory and speech. Side effects depend on the area of the brain being targeted. Some side effects may occur at different times: some may present themselves quickly, and others may not show up until one to two years after treatment. Radiation may cause the brain to swell, which may trigger some of these side effects. Medications may help prevent brain swelling. Patients experiencing any of these side effects should immediately alert their doctor.

Side effects of radiation therapy for breast cancer

After radiation therapy to the breasts, patients may experience swelling, heaviness, tenderness or dryness. Some long-term breast changes may also occur, including slightly darker skin and larger pores. The skin may also be more or less sensitive and feel thicker or firmer than before treatment. To ease irritation around the breast, women should avoid wearing a bra, or wear a soft cotton bra. Doctors should be alerted if fluid builds up in the breast (lymphedema) or if any post-treatment changes occur.

Radiation therapy to the breasts or chest area has a slight risk of damaging the heart, we use advanced technologies to reduce that risk. Some rare side effects impacting the lungs may include radiation pneumonitis, which may include shortness of breath, coughing, chest pain and a low-grade fever. Patients who experience any heart or lung problems should contact their care team immediately.

Side effects of radiation therapy for head and neck cancers

During radiation therapy to the head and neck, it’s important for patients to take care of their gums, teeth, mouth and throat, as they may experience pain, soreness or loss of taste in these areas. Some ways to manage these side effects include avoiding spicy or raw foods, extremely hot or cold foods or beverages, and sugary foods. It’s recommended that patients not smoke, drink alcohol to excess or chew tobacco. In addition to their cancer care team, patients should reach out to a dentist for any mouth and teeth issues.

When to seek medical attention for side effects

Before treatment, patients should consult with their care team about potential side effects related to their specific area of radiation therapy. Those who experience any other noticeable or irregular changes in physical appearance or their physiological state during or after radiation treatment should contact their doctors—the earlier, the better.

What is radiation sickness?

Radiation sickness is a relatively rare condition that results when excessive levels of radiation damage the body. Also called radiation poisoning or acute radiation syndrome, it generally affects people who receive large doses of radiation over a short time period, like those who are near nuclear accidents or explosions. However, it isn’t caused by imaging tests or radiation therapy for cancer.

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