The short answer
Cancer and cancer treatments can cause side effects—problems that happen when treatment affects healthy tissues or organs. Side effects vary from person to person, even among people getting the same treatment. Your health care team can treat many side effects or help you reduce them, so it helps to speak up about any problems you have.
Side effects are problems that occur when treatment affects healthy tissues or organs.
Both the cancer itself and cancer treatments can cause side effects.
Side effects vary from person to person, even among people getting the same treatment.
Your health care team can treat many side effects or find ways to reduce them.
Choose how you want to read this
The whole article, with every detail and caution.
This page is for anyone starting or going through cancer treatment. It explains why side effects happen, when to call your team, and where to find help for specific problems.
Call about a fever right away
Most side effects can wait for your next appointment. A fever during treatment cannot.
- Call your care team straight away, day or night, if your temperature reaches 100.4°F (38°C) or higher. If you cannot reach them quickly, call 911 or go to an emergency room. Also call if you feel shivery, shaky, or suddenly unwell even with a normal reading. During chemotherapy, your white cell count can be too low to fight infection. CDC calls a fever during chemotherapy a medical emergency, not something to sleep off.
- Call 911 or go to an emergency department for sudden shortness of breath, chest pain, heavy bleeding, confusion, a seizure, or a sudden inability to keep fluids down. Do not drive yourself.
Talk with your team before you take any medicine for a fever, even acetaminophen (Tylenol), ibuprofen (Advil) or aspirin. NCI says these can hide signs of a more serious problem. Keep the out-of-hours number your team gave you somewhere you can find it at 3am.
The simple version
Cancer treatments and cancer itself can cause side effects. A side effect is a problem that happens when treatment affects healthy tissues or organs, not just the cancer cells. Because treatment reaches normal parts of the body too, it can cause new problems while it works against the cancer.
The most important thing to know: your health care team can help. They can treat many side effects, or talk with you about ways to reduce them, so you feel better.
Why side effects happen
Cancer treatments are designed to destroy or slow cancer cells. But healthy cells and organs can be affected along the way. When that happens, you may notice problems such as tiredness, an upset stomach, or changes in how you eat. These are side effects.
The cancer itself can also cause problems that feel like side effects. So the two can overlap.
Side effects are different for everyone
Side effects vary from person to person, even among people receiving the same treatment. You might have side effects that a friend or family member with cancer never had. The opposite can be true too. There is no single way that treatment affects everyone.
Because of this, it helps to focus on your own experience rather than comparing yourself with others.
Speak up so your team can help
Tell your doctor about side effects you are having, so you get the care you need to manage them. Speaking up early is one of the most helpful things you can do.
Your health care team can:
- Treat the side effect directly.
- Suggest ways to prevent it or make it less severe.
- Adjust your care so you feel better day to day.
You do not have to simply "put up with" side effects. Reporting them is part of good care.
Two things to raise before treatment starts
Your team needs to know everything you take, not just prescriptions. That includes over-the-counter medicines, vitamins, minerals, and herbal products. NCI says some of these can change how your cancer treatment works. Ask whether any of them could change the way your cancer treatment works.
Ask too whether the treatment could affect your ability to have children. Some options for protecting fertility have to be arranged before treatment begins, so this is a question worth raising early rather than later. See fertility and cancer treatment.
Common side effects to learn about
There are many possible side effects. Which ones you may have depends on your treatment and your body. Some of the ones NCI describes include:
Whole-body effects
- Fatigue, meaning extreme tiredness.
- Pain.
- Anemia, meaning too few red blood cells.
- Infection.
- Sleep problems.
Eating and digestion
- Nausea and vomiting.
- Appetite loss and weight changes.
- Constipation, diarrhea, and other digestion problems.
- Mouth and throat problems.
Hair, skin, and nerves
- Hair loss, called alopecia.
- Nerve problems.
- Skin and nail changes.
Practical side-effect guides
For symptom-specific help, start with the page closest to what is happening. Options include:
- diarrhea during cancer treatment
- constipation during cancer treatment
- mouth sores
- nausea
- fatigue
- appetite loss
- taste changes
- hair loss
- neuropathy
- rash
- fever during chemo
- low white blood cells
- immune-related side effects
These guides focus on what to track, what to ask, and which red flags are worth discussing with your care team before symptoms become harder to manage.
Learning what to expect can make side effects feel less frightening. It can also help you know when to reach out to your team.
Common questions
What is a side effect?
A side effect is a problem that occurs when treatment affects healthy tissues or organs, not just the cancer. Cancer treatments and cancer itself can both cause side effects.
Will I get the same side effects as someone else with my type of cancer?
Not necessarily. Side effects vary from person to person, even among people receiving the same type of cancer treatment. Your experience may be different from someone else's.
Should I tell my doctor about side effects, or try to deal with them myself?
Speak up about any problems you have. Your health care team can treat side effects and talk with you about ways to reduce them, so you feel better. Telling your doctor helps you get the care you need.
What kinds of side effects can cancer treatment cause?
Many kinds. NCI lists side effects that range from fatigue, hair loss, nausea and vomiting, and pain to appetite and weight changes, anemia, infection, nerve problems, and more. Which ones you may have depends on your treatment and your body.
Questions to ask your doctor
Being prepared helps you get the most out of your appointments. Save or print these questions.
Tap a question to save it to your list (kept on this device).
Your next step
What needs a call today, what needs an emergency room, and what can wait.
Talk with a trained specialist or navigator
Cancer Explained provides educational guidance, but does not replace trained specialists, social workers, or your medical team.
Talk to a trained cancer information specialist
Free, confidential assistance from NCI Cancer Information Service via phone, chat, or email.
Contact your oncology team
Locate after-hours contact numbers, portal messages, or urgent triage phone lines.
Find a patient navigator
Get one-on-one help with appointments, logistics, translation, and care coordination.
Find a genetic counselor
Discuss inherited mutation risk, family history, and genetic testing options.
Find an oncology social worker
Access emotional counseling, family support groups, and mental health resources.
Find a financial navigator
Locate copay assistance foundations, grant programs, and lodging/travel support.
Find a clinical-trial specialist
Search matching studies and speak with NCI trial information specialists.
Get urgent help
Fever of 100.4°F (38°C) or higher during chemo, severe pain, or trouble breathing: call your cancer care team right away, day or night. Call 911 for an emergency.
Know someone who needs this?
Plenty of people are looking for something like this and do not know where to start. If this would help a friend or someone you love, send it on — we have written an opening line so you do not have to stare at an empty message. You can change every word of it.
Your message is written and sent in your own email or messaging app — we never see who you send it to, and nothing is added to any list.
Plain-language explanation of the published sources cited on this page. AI-assisted, source-checked, not clinician-reviewed.
Sources last checked: 2026-08-13 what this meansLast updated: 2026-09-29Next planned review: 2027-02-03
Review details and limits
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, and this 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 then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
General education — varies by person. Answers genuinely differ between people. This page explains what commonly varies and points you to your care team 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.
Words to know
Tap any term to see what it means.
Knowledge check
0 of 4 answered
This self-assessment checks understanding of educational content only. It is not medical advice.
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, and this 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 then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. 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.
Read more about our editorial process, our use of AI, and our corrections policy.
Spotted a problem? Report an error — a factual mistake, broken or outdated source, confusing wording, or anything that seems unsafe. Please do not include names, medical record numbers, dates of birth, addresses, or other identifying medical information in your report.
After using this page, do you understand what to do next?
Anonymous — we only record the answer, never who gave it.