Updated: August 2026
Cancer treatment can save lives, shrink tumours, prevent cancer from returning and relieve symptoms. But treatments such as chemotherapy and radiotherapy can also affect healthy cells and tissues, producing side effects.
One of the most important things to understand is that not everyone experiences the same side effects.
Two people receiving cancer treatment may feel very different. Side effects depend on the treatment being used, its dose, the type and location of the cancer, other treatments being given and the person's general health. (Cancer.gov)
Chemotherapy and radiotherapy can also produce different effects. Hair loss, for example, is not inevitable with every chemotherapy drug, while radiotherapy usually causes effects mainly in or around the part of the body being treated.
Knowing what may happen can make treatment less frightening and, more importantly, help patients recognise when they need medical attention.
What Is Chemotherapy?
Chemotherapy uses medicines to kill cancer cells or stop them from growing.
Cancer cells often divide rapidly. Many traditional chemotherapy medicines target rapidly dividing cells, but some healthy cells also divide quickly. These include cells in the bone marrow, digestive tract and hair follicles.
When these healthy cells are affected, side effects can occur. (Cancer.gov)
Chemotherapy may be used to:
cure certain cancers
reduce the chance that cancer returns
shrink a tumour before surgery or radiotherapy
destroy cancer cells remaining after another treatment
slow advanced cancer
relieve symptoms caused by cancer
Chemotherapy is only one form of systemic cancer treatment. Immunotherapy, hormone therapy and targeted therapies work differently and can have their own side effects.
What Is Radiotherapy?
Radiotherapy, also called radiation therapy, uses high doses of radiation to damage the DNA of cancer cells.
Cells with sufficiently damaged DNA stop dividing or die.
Radiotherapy can be used to cure some cancers, reduce the chance of recurrence, shrink tumours or relieve symptoms. (Cancer.gov)
Modern radiotherapy is carefully planned to deliver radiation to the intended treatment area while reducing unnecessary exposure of surrounding healthy tissues.
Even with careful planning, nearby healthy cells can be affected. This is why radiotherapy can cause side effects.
Chemotherapy and Radiotherapy Are Not the Same
Although both are cancer treatments, their effects on the body can be quite different.
Chemotherapy medicines may circulate through much of the body, depending on how they are administered.
External-beam radiotherapy is directed toward a particular area.
That distinction explains why chemotherapy may produce more widespread effects, while many radiotherapy effects depend strongly on which part of the body receives radiation. (Cancer.gov)
For example, radiotherapy to the pelvis may affect the bowel or bladder, while treatment to the head and neck can affect the mouth, throat and salivary glands.
Common Side Effects of Chemotherapy
There is no single list that applies to every chemotherapy regimen.
Some people experience several side effects. Others experience relatively few.
1. Fatigue
Fatigue is one of the most common problems experienced during cancer treatment.
This is more than simply feeling sleepy.
Cancer-related fatigue can feel like persistent physical or mental exhaustion that is disproportionate to recent activity.
Treatment, anaemia, poor nutrition, sleep disturbance, pain, emotional stress and cancer itself can all contribute.
Patients should tell their cancer-care team about significant fatigue rather than assuming nothing can be done.
2. Nausea and Vomiting
Some chemotherapy medicines can cause nausea and vomiting.
However, the idea that chemotherapy inevitably means uncontrollable vomiting is outdated.
Effective anti-nausea medicines are available, and these can often prevent or substantially reduce nausea and vomiting when appropriately prescribed. (Cancer.gov)
Patients should take anti-nausea medicines according to their treatment team's instructions rather than waiting until symptoms become severe.
Persistent vomiting needs attention because it can cause dehydration, electrolyte disturbances and weight loss.
3. Hair Loss
Some chemotherapy medicines damage rapidly dividing cells in hair follicles.
This can cause thinning or complete hair loss.
But:
not every chemotherapy drug causes hair loss.
The degree of hair loss depends on the medicines and doses used.
Hair may be lost from the scalp and sometimes other parts of the body.
For many people, hair begins growing again after treatment finishes, although its initial texture or appearance can sometimes differ.
4. Mouth and Throat Problems
Chemotherapy can affect the rapidly dividing cells lining the mouth and digestive tract.
Some patients develop:
mouth sores
soreness
dry mouth
altered taste
difficulty eating
increased risk of oral infection
Good oral care can be particularly important during treatment.
Patients should ask their oncology team which mouth-care products are appropriate because some products may irritate an already sensitive mouth.
5. Reduced Blood Cell Counts
Bone marrow produces blood cells, and some chemotherapy medicines suppress its activity.
This can reduce different types of blood cells.
Low White Blood Cells
A reduction in infection-fighting white blood cells, particularly neutrophils, can increase infection risk.
This is called neutropenia.
Infection during neutropenia can become serious very quickly.
Low Red Blood Cells
A reduction in red blood cells can cause anaemia.
Possible symptoms include:
tiredness
weakness
dizziness
shortness of breath
rapid heartbeat
Low Platelets
Platelets help blood clot.
Low platelet levels can increase the risk of unusual bleeding or bruising.
Blood tests are therefore commonly performed during chemotherapy to monitor blood-cell counts.
Fever During Chemotherapy Can Be an Emergency
This deserves special emphasis.
A fever during chemotherapy should not automatically be treated at home as malaria, typhoid or an ordinary infection.
Some chemotherapy treatments reduce neutrophils, leaving the body less able to fight infection.
NCI advises people receiving cancer treatment to contact their healthcare team urgently for signs of infection, including a temperature of 38°C or higher. Infections during cancer treatment can be life-threatening. (Cancer.gov)
Patients should follow the specific fever instructions given by their own oncology centre because thresholds and emergency procedures may differ.
Do not simply take paracetamol to hide a fever without contacting the cancer-care team when you have been instructed to report fever during chemotherapy.
6. Diarrhoea or Constipation
Chemotherapy, anti-nausea medicines, pain medicines and changes in diet or activity can affect bowel movements.
Some patients develop diarrhoea.
Others become constipated.
Severe or persistent diarrhoea can cause dehydration and electrolyte problems, while significant constipation may also require treatment.
Tell your cancer-care team rather than repeatedly self-medicating.
7. Changes in Appetite and Weight
Cancer and its treatment can affect:
appetite
taste
smell
swallowing
digestion
body weight
Some people lose weight because eating becomes difficult.
Others may gain weight depending on medicines, activity levels and other factors.
Maintaining adequate nutrition during cancer treatment can be important, particularly when the body is recovering from intensive therapy.
A dietitian experienced in cancer care may be helpful when eating becomes difficult.
8. Peripheral Neuropathy
Some chemotherapy medicines can damage peripheral nerves.
This may cause:
numbness
tingling
burning sensations
pain
weakness
problems with balance
difficulty performing tasks requiring fine hand movements
Tell the cancer-care team about these symptoms early.
Neuropathy can sometimes influence treatment decisions.
9. Skin and Nail Changes
Depending on the medicines used, chemotherapy can cause changes such as:
dry skin
rashes
increased sensitivity
changes in nail colour
brittle nails
Severe skin reactions should be reported promptly.
10. Fertility and Sexual Health
Some chemotherapy medicines can temporarily or permanently affect fertility.
Effects depend on factors including:
medicine used
treatment dose
age
sex
baseline reproductive health
Cancer itself and its treatment can also affect sexual health.
People who may want biological children in the future should ideally discuss fertility preservation before treatment begins, whenever circumstances allow.
Common Side Effects of Radiotherapy
Radiotherapy side effects need to be understood differently.
The area being treated matters enormously.
NCI notes that fatigue is common, while other effects depend largely on the body part receiving radiation. (Cancer.gov)
1. Fatigue
Fatigue can develop gradually during radiotherapy.
Some people continue working and performing most usual activities. Others need substantially more rest.
Energy levels often improve after treatment, although recovery time varies.
2. Skin Changes
External-beam radiotherapy can affect skin within the treatment area.
Possible changes include:
redness or darkening
dryness
itching
tenderness
peeling
The cancer-care team should provide instructions about caring for treated skin.
Do not automatically apply creams, herbal preparations, perfumes or other products to the treatment area without checking whether they are suitable.
3. Hair Loss in the Treatment Area
Radiotherapy can cause hair loss, but unlike many chemotherapy regimens, it generally affects hair within the area being irradiated.
Radiotherapy to the head, for example, may affect scalp hair.
Pelvic radiotherapy does not normally make scalp hair fall out.
Hair may regrow after treatment, although higher radiation doses can sometimes produce permanent changes.
4. Head and Neck Radiotherapy
Radiation directed toward the head or neck may cause:
mouth soreness
dry mouth
taste changes
difficulty swallowing
skin changes
fatigue
dental problems
changes in thyroid function in some patients
Maintaining nutrition can become challenging if eating or swallowing becomes painful.
Patients receiving head and neck radiotherapy may therefore receive specialised dental, nutritional and swallowing support.
5. Chest Radiotherapy
Depending on the exact treatment field, chest radiotherapy can cause:
fatigue
skin changes
difficulty swallowing
cough
shortness of breath
New or worsening breathing difficulties should be discussed promptly with the treatment team. (Cancer.gov)
6. Abdominal Radiotherapy
Radiation directed toward parts of the abdomen may cause:
nausea
vomiting
diarrhoea
fatigue
skin changes
The specific effects depend on which organs are exposed.
7. Pelvic Radiotherapy
Pelvic treatment can affect the bowel, bladder and reproductive organs.
Possible effects include:
diarrhoea
urinary symptoms
fatigue
skin changes
sexual-health problems
fertility problems
Again, not everyone experiences all of these effects. (Cancer.gov)
Does Radiotherapy Make You Radioactive?
This depends on the type of radiotherapy.
People receiving external-beam radiotherapy generally do not become radioactive from the treatment.
They can normally be around family members after a treatment session.
Some internal or systemic radiation treatments are different and may require temporary precautions.
Your radiation team should explain any precautions required for the specific treatment you receive.
Do Cancer Treatment Side Effects Mean the Treatment Is Working?
No.
This is an important myth.
Having severe chemotherapy side effects does not prove that chemotherapy is killing more cancer cells.
Likewise, having few side effects does not mean treatment is ineffective.
NCI specifically notes that chemotherapy side-effect severity does not tell you how effectively chemotherapy is treating the cancer. (Cancer.gov)
Treatment response is assessed using appropriate clinical examinations, laboratory tests and imaging.
When Do Side Effects Begin?
There is no universal timeline.
Some chemotherapy effects can develop within hours or days.
Others appear after repeated treatment cycles.
Radiotherapy side effects may build gradually as treatment continues.
Many improve after treatment finishes as healthy tissues recover. However, some effects can persist, and others can appear months or years later. These are sometimes called late effects. (Cancer.gov)
What Are Late Effects of Cancer Treatment?
Cancer survivors may occasionally develop health problems long after treatment.
Possible late effects depend heavily on:
treatment received
radiation area and dose
chemotherapy medicines
age at treatment
other health conditions
Potential late effects can involve organs such as the heart, lungs, kidneys, nerves or reproductive system.
This does not mean everyone who receives cancer treatment will develop long-term complications.
It means follow-up care remains important even after treatment has ended.
When Should You Contact Your Cancer-Care Team?
Patients should receive individual instructions because risks differ between treatments.
Contact your treatment team promptly if you develop symptoms they have instructed you to report.
Particularly important problems can include:
fever during chemotherapy
chills or other signs of infection
unusual bleeding
severe or persistent vomiting
severe diarrhoea
inability to drink enough fluid
significant dehydration
new or worsening shortness of breath
severe mouth sores preventing eating or drinking
confusion
severe weakness
rapidly worsening pain
redness, swelling or discharge around a catheter or treatment access site
Do not wait for the next routine appointment if your oncology team has told you a particular symptom requires immediate contact.
Can Cancer Treatment Side Effects Be Managed?
Often, yes.
Modern supportive cancer care includes many strategies for preventing or controlling treatment effects.
Depending on the problem, these can include:
anti-nausea medicines
pain management
nutritional support
mouth care
medicines to manage bowel problems
treatment for infection
blood transfusion when appropriate
medicines affecting blood-cell production in selected situations
skin-care measures
physiotherapy
psychological support
The appropriate intervention depends on the individual patient.
Side effects should therefore be reported rather than silently endured. NCI specifically encourages patients to tell their healthcare team about treatment-related problems so they can be managed appropriately. (Cancer.gov)
Should You Use Herbal Remedies During Chemotherapy?
Do not assume a product is safe simply because it is described as natural.
Herbs, supplements and traditional remedies can sometimes interact with cancer medicines or affect how medicines are processed by the body.
Tell your oncologist or pharmacist about supplements and herbal products you are considering.
Do not stop prescribed cancer treatment in favour of an unproven alternative therapy without discussing the consequences with your medical team.
Eating During Cancer Treatment
There is no single “cancer diet” suitable for everyone undergoing chemotherapy or radiotherapy.
Nutritional needs can change depending on:
cancer type
treatment
appetite
swallowing ability
bowel symptoms
body weight
other medical conditions
Someone struggling with nausea may need a different approach from someone with painful swallowing or severe diarrhoea.
NCI notes that adequate calories and protein can be particularly important during radiotherapy because the body needs nutrition while tissues heal. (Cancer.gov)
Frequently Asked Questions
Does everyone lose their hair during chemotherapy?
No.
Hair loss depends on the chemotherapy medicines and doses being used.
Is radiotherapy painful?
External-beam radiation itself is generally not felt while it is being delivered. Side effects can develop during or after the course of treatment.
Will radiotherapy make me radioactive?
External-beam radiotherapy does not normally make the patient radioactive. Certain internal and systemic radioactive treatments may require temporary precautions.
Does severe nausea mean chemotherapy is working?
No.
Side-effect severity is not a reliable measure of cancer-treatment effectiveness. (Cancer.gov)
Can chemotherapy lower immunity?
Some chemotherapy medicines reduce infection-fighting white blood cells, including neutrophils. This can increase infection risk.
Why is fever dangerous during chemotherapy?
A fever can indicate infection when the immune system is suppressed. Such infections can become life-threatening and may require urgent treatment. (Cancer.gov)
Will radiotherapy cause hair loss everywhere?
Usually not. Hair loss from radiotherapy generally occurs within the area receiving radiation.
Do all radiotherapy patients experience the same effects?
No. Effects depend heavily on the area treated, radiation dose, other treatments and individual factors. (Cancer.gov)
Can side effects continue after treatment?
Yes. Many improve after treatment ends, but some can persist or appear later. (Cancer.gov)
Key Takeaways
Chemotherapy and radiotherapy can both cause side effects, but they should not be treated as though they affect the body in exactly the same way.
Chemotherapy side effects depend heavily on the drugs and doses used.
Radiotherapy effects depend particularly on the body area being treated.
Not everyone receiving chemotherapy loses their hair.
Not everyone receiving radiotherapy develops severe skin problems.
Side-effect severity does not tell you whether treatment is working.
Many side effects can now be prevented or managed effectively.
And most importantly:
patients receiving cancer treatment should know which symptoms their treatment centre considers urgent, especially fever and signs of infection during chemotherapy.
References and Further Reading
National Cancer Institute: Chemotherapy to Treat Cancer
National Cancer Institute: Chemotherapy and You
National Cancer Institute: Radiation Therapy Side Effects
National Cancer Institute: Infection and Neutropenia During Cancer Treatment
National Cancer Institute: Cancer Treatment Side Effects
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