The short answer
Radiation runs weekdays for several weeks with short sessions. Fatigue builds and peaks around the midpoint, and skin and mucous membrane reactions often peak in the final week and shortly after.
Most visits last 30 to 60 minutes with the beam on for only one to five minutes, and external beam radiation does not make you radioactive.
More than 80 percent of people having chemotherapy or radiation report fatigue, and it is not relieved by sleep or rest.
Radiation fatigue typically rises after treatment starts, peaks around the midpoint, then levels off until the course ends.
Skin and mouth or throat reactions often worsen through the last week and for one to two weeks after the final session before improving.
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The full explanation.
What the daily routine looks like
Before treatment starts you have a planning session, called simulation. Marks or small permanent dots go on the skin, so you are positioned the same way each time. If the treatment area is the head or neck, a mold or fitted mesh mask may be made. Most external beam courses run once a day, Monday to Friday. The number of weeks depends on the cancer and the goal. NCI notes that most visits last 30 minutes to an hour. The beam itself is on for only one to five minutes. External beam radiation does not make you radioactive. You can safely be around children and pregnant people.
The routine is repetitive and undramatic, and that surprises many people. You feel nothing during the treatment itself. People often say the logistics, the parking and the daily travel are harder than the sessions.
Fatigue that builds
Fatigue is the most common effect. NCI reports that more than 80 percent of people having chemotherapy or radiation get it. Sleep and rest do not relieve it, and it can follow very little activity. With radiation it usually rises after treatment starts. It peaks around the midpoint, then levels off until the course ends. People routinely get caught out in week three or four, after feeling fine at the start. The usual advice is gentle regular activity, not complete rest.
Skin changes
The treated skin can turn red or darker. It can go dry, itchy, flaky or peeling. In some areas it can blister or weep. It behaves like a sunburn that keeps being reapplied. The usual advice runs like this. Wear loose clothing in soft fabrics. Use lukewarm water and mild soap. Do not rub or scrub. Keep adhesive tape off treated skin. Avoid heat or ice packs unless your team approves. And keep powders, perfumes and deodorants off the area unless your team has cleared them. Ask whether creams should be avoided in the hours before a session. Sun protection matters afterwards, and treated skin often stays darker or more sensitive long term.
The timing people find hardest
Side effects usually peak late. Skin reactions and sore mouths or throats commonly get worse through the final week. They can keep worsening for one to two weeks after the last session, then improve. So finishing treatment and then feeling worse is expected. It is not a sign something has gone wrong. Still, tell your team when it happens, so symptoms can be managed.
What depends on the area treated
Effects are mostly limited to the part of the body being treated. Head and neck radiation can bring mouth and throat soreness, dry mouth, taste changes and trouble swallowing. It can also cause hair loss in the treated area and thyroid changes. Chest treatment can cause cough, breathlessness and throat discomfort. Abdomen and pelvis can bring nausea, diarrhea, bladder irritation, and fertility or sexual changes. Breast radiation commonly causes tenderness, swelling and skin changes.
Early and late effects
Early effects arise during or soon after treatment. Most improve within weeks to a few months, as healthy cells repair. Late effects can appear months or years later. They depend on the area treated, on earlier therapies, and on other factors such as smoking. Ask which late effects apply to your treated area, and what follow-up is advised. This is easy to leave unaddressed once the daily visits stop.
When to get help sooner
Tell your radiation team at any daily visit about new or worsening symptoms. You do not need to wait for a scheduled review.
- Call 911 or go to an emergency department if you have trouble breathing, or your throat closes up so much that swallowing is not possible. This matters most during head, neck or chest treatment.
- Call 911 or go to an emergency department if your temperature reaches 100.4 degrees Fahrenheit (38 degrees Celsius) or higher while you are also on chemotherapy, or if any fever comes with shaking chills, confusion or fast breathing. The CDC states that a fever during chemotherapy is a medical emergency, because an infection can become life-threatening within hours when white cells are low.
- Call your care team the same day if your temperature reaches that level on radiation alone. Call too if treated skin breaks open, blisters or weeps, if pain is beating your current medicine, or if you cannot drink enough to stay hydrated. During head and neck treatment, call if your mouth is so sore that you are skipping meals.
- Call your care team within a day or two if pelvic or abdominal treatment brings several more loose stools a day than usual, blood in stool or urine, or pain on passing urine.
Sources
Words to know
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Common questions
Will I feel the radiation?
No. Nothing is felt during the treatment itself. Most visits last 30 minutes to an hour, and most of that time is spent getting you positioned correctly; the beam is on for only one to five minutes. People often describe the daily logistics, parking and travel as harder than the sessions.
Why do I feel worse after treatment ends?
Side effects usually peak late. Skin reactions and sore mouths or throats commonly worsen through the final week and for one to two weeks after the last session before improving. Finishing and then feeling worse is an expected sequence rather than a sign something has gone wrong, though it is worth telling your team when it happens so symptoms can be managed.
Am I radioactive around my family?
Not with external beam radiation. NCI states you can safely be around other people, including pregnant women, babies and young children. Different rules apply to some internal radiation and radioactive drug treatments, so ask specifically if you are having one of those.
How should I look after my skin?
General advice is loose clothing in soft fabrics, lukewarm water and mild soap, no rubbing or scrubbing, no adhesive tape on treated skin, no heat or ice packs without approval, and no powders, perfumes or deodorants on the area unless your team has cleared them. Ask whether creams should be avoided in the hours before a session, and about sun protection afterwards, since treated skin often stays darker and more sensitive.
Does everyone get the same side effects?
No. Effects are largely limited to the part of the body being treated, so head and neck, chest, abdomen, pelvis and breast treatments each bring different problems. Severity also varies widely between people receiving the same dose, which is why comparing yourself to someone else's course is rarely useful.
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Written by: Cancer ExplainedSources last checked: 2026-08-13 what this meansLast updated: 2026-08-13Next planned review: 2027-01-30
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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