Side Effects of Chemotherapy and Radiotherapy; A Complete Guide for Patients

What you need to know and how to act

If you or a loved one has started cancer treatment (chemotherapy, radiotherapy or immunotherapy), this guide will help you understand what side effects may occur, how to recognize them and when you should contact your doctor urgently. The information is written in simple language, away from complicated medical terms.

⚠️ Important note: This guide is for informational purposes only. It does not replace the advice of your oncologist. If you experience serious symptoms, contact your medical team immediately.

Why Do Side Effects Occur?

Chemotherapy works by destroying rapidly dividing cells — including cancer cells. The problem is that healthy, fast-growing cells are also affected: hair, digestive lining, blood-producing cells in the bone marrow.

Radiation therapy uses radiation to kill cancer cells in a specific area of the body. Side effects depend on which organ is treated.

Immunotherapy stimulates the immune system to attack cancer, but sometimes the immune reactions can be too strong and harmful to other organs.

By knowing in advance what to expect, you can be more prepared and communicate better with your doctor.

How is the severity of side effects measured?

Doctors use a standardized scale to describe how serious the side effects are:

Degree	Severity	What does this mean
0	No effect	No symptoms
1	Easy	The symptom is present, but it does not interfere with your daily activities
2	Moderate	Limits some activities; may require treatment
3	Severe	Significantly limits what you can do; may require hospitalization
4	Potentially lethal	Requires medical emergency/hospital

Practical tip: When describing your symptoms to your doctor, be specific about how they’re affecting your daily life. This helps them understand how serious they are and whether they need to adjust your treatment.

Blood Problems

Chemotherapy affects the bone marrow — where blood cells are made. Here’s what you need to monitor:

Low White Blood Cells (Neutropenia) — Risk of Infection

White blood cells are the “soldiers” that defend you against infections. When they are lacking, the body becomes vulnerable.

Warning signs:

Fever above 38°C, even without other symptoms
Chills, night sweats
Severe fatigue, weakness

What to do:

Contact your doctor IMMEDIATELY if you have a fever after chemotherapy — don’t wait
The doctor will prescribe medications that stimulate the production of white blood cells.
In case of fever, you will receive strong antibiotics intravenously

How to protect yourself:

Wash your hands frequently and thoroughly.
Avoid contact with people who have colds or are sick.
Eat well-cooked foods and avoid raw foods.
Follow the vaccination schedule recommended by your doctor.

Low Platelets (Thrombocytopenia) — Risk of Bleeding

Platelets help your blood clot. When there are few of them, you bleed more easily.

Warning signs:

Small red spots on the skin that appear for no reason
Unusual bruises or bruises that appear out of nowhere
Nosebleeds, gums, or blood in the urine/stool
Unusual bleeding from any orifice

What to do:

Notify your doctor if you notice these signs.
If the levels are very low, you may receive platelet transfusions.

How to protect yourself:

Avoid blood-thinning medications (aspirin, ibuprofen) without your doctor’s advice.
Be gentle with your oral health (use a soft toothbrush)
Avoid contact sports

Anemia — Extreme Fatigue

When red blood cells are missing, the blood lacks oxygen.

Warning signs:

Extreme fatigue, much greater than usual
Paleness, discolored lips and nails
Difficulty breathing even with little exertion
Rapid heartbeat
Dizziness

What to do:

Tell your doctor; he or she may prescribe specific medications or transfusions.

Digestive Problems (Stomach and Intestines)

Nausea and Vomiting

This is the most well-known side effect of chemotherapy, but also the one best controlled with modern medications.

Types of nausea:

Acute: occurs within the first 24 hours after treatment
Delayed: occurs after 24 hours and can last for several days
Anticipatory: occurs before treatment out of fear (psychological reaction)

Factors that increase the risk:

Women and people under 60 are at higher risk
Anxiety and previous unpleasant experiences
Certain chemotherapy drugs (cisplatin, cyclophosphamide)

What medications help:

5-HT3 antagonists (ondansetron, granisetron)
NK-1 antagonists (aprepitant)
Corticosteroids (dexamethasone)
Newer, highly effective medications

Practical tips:

Your doctor will prescribe antiemetics BEFORE chemotherapy, not after.
Eat small, frequent meals (5-6 per day)
Choose cold or room temperature foods (the smell of hot foods makes nausea worse)
Avoid fatty, spicy and strong-smelling foods
Lie down for a while after treatment.
Ginger tea can help slightly

When to contact your doctor:

If you have more than 6 episodes of vomiting in 24 hours
If you are unable to keep liquids down for more than 24 hours
If you feel dizzy and weak due to dehydration

Mouth Ulcers (Mucositis)

Chemotherapy and radiation therapy can cause painful sores in the mouth and throat.

Signs:

Red, painful ulcers on the lining of the mouth
Difficulty eating and swallowing
Unpleasant taste or loss of taste
Halitosis, bleeding gums

What do you prevent:

Dental consultation BEFORE starting treatment
Rigorous oral hygiene: soft toothbrush, rinsing with saline or bicarbonate 4-6 times a day
Avoid alcohol and mouthwash containing alcohol

What do you eat:

Soft, wet foods: soup, puree, yogurt, gelatin
Avoid hot, acidic, irritating foods (citrus, spicy, pickled)
Drink plenty of fluids.

Diarrhea

Signs:

More than 2-3 loose stools per day (more than usual)
Abdominal cramps, pain

When to contact your doctor:

If you have more than 6-7 stools a day
If you notice blood in your stool
If fever occurs

What do you do:

Avoid fatty, high-fiber, or irritating foods
Eat small, frequent portions.
Drink fluids: water, chamomile tea, rehydration solutions
The doctor may prescribe anti-diarrhea medications.

Constipation

It can occur due to medications, inactivity, or diet.

What do you prevent:

Eat foods high in fiber (fruits, vegetables, whole grains)
Drink plenty of water (at least 2 liters per day)
Move, even slightly
The doctor may prescribe laxatives

Fatigue (Oncological Asthenia)

This is the most common side effect and, paradoxically, the one most ignored by patients.

Signs:

Extreme fatigue that doesn’t go away with rest
Lack of energy for daily activities
Difficulty concentrating

To differentiate from anemia:

If fatigue is accompanied by paleness, shortness of breath on mild exertion, and a rapid heartbeat — it could be anemia.
Blood tests will check hemoglobin

What do you do:

Moderate physical activity (paradoxically, light exercise reduces fatigue) — 30 minutes of walking a day helps
Regular sleep schedule — going to bed and waking up at fixed times
Proper nutrition — protein and calorie foods
Prioritize: do the important things today; delegate the rest
Strategic rest — don’t stay horizontal all day

Tip: If your fatigue is very severe and prevents you from doing your daily activities, tell your doctor. He or she may adjust your treatment.

Skin and Hair Problems

Hair Loss (Alopecia)

This usually occurs 1-2 weeks after the first cycle and is emotionally difficult for many.

What to know:

It affects not only the hair on the head, but also eyebrows, eyelashes and body hair.
It is always temporary — hair regrows 1-3 months after treatment
Texture and color may vary slightly upon baking.
Not all patients lose all their hair — it depends on the drug

What helps you:

Scalp cooling caps (cold cap), applied before and after treatment, can reduce hair loss in some cases.
Wigs, scarves, hats
Specialized cosmetics for eyebrows and eyelashes
Psychological support — it’s normal to be emotionally difficult

Redness and Pain on the Palms and Soles (Hand-Foot Syndrome)

Certain drugs (capecitabine, 5-fluorouracil, doxorubicin) accumulate in the skin, causing symptoms.

Signs:

Redness, swelling, pain on the palms and soles
Burning sensation, tingling (appears first, before redness)
In severe cases: blisters, cracks, inability to walk

Classification by severity:

Grade 1: Mild redness, no pain — continue treatment, apply moisturizers
Grade 2: Pain that limits activities — doctor may reduce dose
Grade 3: Severe pain — treatment is temporarily discontinued

What do you prevent:

Moisturizers with urea (10-40%) applied twice a day, from the first week
Avoid activities that create friction: jogging, intense sports, gardening activities
Wear comfortable, slightly adjusted shoes
Avoid hot water; use lukewarm water
Local cooling of the hands/feet during infusion helps with some medications

Skin Irritation from Radiotherapy (Radiation Dermatitis)

It affects almost all patients undergoing radiotherapy, but the severity varies.

Progressive signs:

Grade 1: Mild erythema (like mild sunburn)
Grade 2: Peeling, swelling
Grade 3: Extensive areas of moist desquamation, possible skin breaks

What do you prevent:

Use fragrance-free emollient creams daily on the treated area
Wash with lukewarm water and mild soap, 5 minutes maximum
Avoid direct sunlight on the irradiated area.
Do not apply other creams, perfumes, or cosmetics unless your doctor has approved them.
Wear soft cotton clothes that don’t rub the area.

When to contact your doctor:

If blisters or skin breaks appear
If the irritation does not improve with standard creams

Skin Color Changes (Hyperpigmentation)

Some medications cause darker areas on the skin, nails, or in the mouth.

What do you prevent:

Rigorous sun protection (SPF 30+) throughout the treatment
These usually improve after treatment ends.

Neurological Problems (Nerves and Brain)

Tingling and Numbness in Hands and Feet (Peripheral Neuropathy)

Certain chemotherapeutics (platinum, taxanes, vincristine) affect peripheral nerves.

Signs:

Tingling and numbness starting in the fingertips (hands and feet)
Burning sensation or “electric shock”-like pain
Loss of balance, increased risk of falls
Difficulty with fine activities: buttons, writing, picking up objects

What to do:

Report these symptoms IMMEDIATELY — early intervention prevents permanent damage
The doctor may reduce the dose or change the medication.
Specific medications for nerve pain may be prescribed (duloxetine, gabapentin)

How to protect yourself:

Increased attention to the risk of falls
Wear shoes with good grip
Good lighting in the house
Increased alertness to fatigue and compromised balance

Confusion and Concentration Problems (“Chemo Brain”)

Many patients report a “mental fog” during and after treatment: memory difficulties, poor concentration, slower thinking.

Signs:

Difficulty concentrating
Poor memory, forgetfulness
Slower mental processing

What do you prevent:

Cognitive exercises: logic games, books, puzzles
Regular physical activity
Quality sleep
Mindfulness and relaxation techniques
It usually improves a few months after treatment.

Alarm signal:

Severe confusion, hallucinations, seizures — requires immediate medical evaluation

Pulmonary (Lung) Problems

Inflammation of the Lungs (Pneumonitis)

It can occur weeks or months after chemotherapy, immunotherapy, or thoracic radiotherapy.

Signs:

Persistent dry cough
Increasingly difficult breathing, even at rest
Mild fever (37.5-38.5°C)
Feeling of heaviness or discomfort in the chest

Alarm signal:

Sudden difficulty breathing
Blood oxygen saturation below 90% — immediate presentation to hospital

What is happening:

The doctor takes an X-ray or chest CT scan.
Respiratory function tests are performed
The causative drug is stopped or suspended
Corticosteroids are prescribed to reduce inflammation

Blood Clots in the Pulmonary (Pulmonary Embolism)

Cancer patients are at higher risk.

Signs:

Unilateral swelling of one leg, pain, redness
Sudden shortness of breath
Chest pain, palpitations
Dizziness

Red flag: This is a medical emergency — go to the emergency room immediately.

How to prevent:

Mobilize as frequently as possible, avoid prolonged standing
Abundant hydration
Some high-risk patients receive preventive anticoagulant medications

Cardiac (Heart) Problems

Weakening of the Heart Muscle (Cardiomyopathy)

Some chemotherapeutics, especially anthracyclines (doxorubicin), can affect the heart, often without initial symptoms.

Signs:

Difficulty breathing, especially with exertion
Unusual fatigue
Swelling of the legs (edema)
Irregular heartbeat

What do you do:

The doctor monitors the heart with periodic ultrasounds and blood tests.
If problems are detected, cardio-active drugs can help
Moderate physical activity, healthy diet

High Blood Pressure

Common with certain targeted therapies.

What do you do:

Measure your blood pressure at home in the first few weeks
Report values above 150/100 mmHg
The doctor will adjust the treatment

Inflammation of the Heart Muscle (Myocarditis) — from Immunotherapy

Rare, but severe.

Signs:

Chest pain
Palpitations, irregular heartbeat
Difficulty breathing, fever

Red flag: Contact your doctor immediately if these symptoms occur during immunotherapy.

Kidney and Urinary Problems

Kidney Damage

Certain medications (especially cisplatin) can damage the kidneys.

Signs:

Reduction in the amount of urine
Hematuria (blood in urine) — see a doctor urgently
Increased creatinine and urea in blood tests

What do you prevent:

Abundant hydration before and after treatment is essential
Strictly follow the hydration recommendations of the medical team
Renal tests are checked at each cycle

Blood in Urine (Hemorrhagic Cystitis)

Associated with some medications (cyclophosphamide).

Red flag: Contact your doctor immediately if you notice blood in your urine.

Metabolic Imbalances

Tumor Lysis Syndrome

It occurs at the beginning of treatment, when tumor cells die rapidly and release their contents into the blood.

Signs:

Severe muscle cramps
Irregular heart rhythm
Reduced urination
Confusion

It usually occurs in the first days of treatment in patients at risk, which is why blood tests are intensively monitored during this period.

High Blood Sugar

Common in patients receiving corticosteroids.

Signs:

Excessive thirst
Frequent urination

What to do: Report to your doctor; he or she may adjust your medication.

Allergic Reactions

They can occur during infusion with certain medications.

Mild signs:

Itching, skin rash
Light leaves

Immediate alarm signal:

Difficulty breathing
Swelling of the lips, tongue, or throat
Feeling faint
Rapid heartbeat

What to do: IMMEDIATELY notify the nurse/doctor in the treatment room. The medication is stopped and emergency treatment is administered.

Hearing and Vision Problems

Hearing Loss

Some chemotherapy drugs (cisplatin) can affect hearing, usually at high frequencies (ringing in the ears, difficulty hearing high-pitched sounds).

What do you do:

Hearing testing is recommended periodically during treatment.
Report any changes

Dry and Irritated Eyes

Some medications cause dry eyes.

What do you do:

Artificial bait helps
Ophthalmological consultation if symptoms are severe

Joint and Muscle Problems

Diffuse joint and muscle pain are common, especially with certain medications (taxanes).

What do you do:

Physiotherapy, massages
Simple analgesics as recommended by a doctor
Hot local apps

Nutrition and Hydration — The Therapeutic Tool You Can Control

Good nutrition can reduce the severity of some side effects and support recovery.

General tips:

Small and frequent meals (5-6 per day) to combat nausea
Cold or room temperature foods (the smell of hot foods makes nausea worse)
Increased protein intake (chicken, fish, lean meat, eggs, dairy, beans) for tissue recovery
Adequate hydration — minimum 2 liters per day, more if you have vomiting or diarrhea
Avoid raw or poorly processed foods during periods when immunity is weak.
Easily digestible foods: soups, purees, yogurt, soft cheeses, white bread

When to consult an oncology nutritionist:

If you lose more than 5% of your weight in the first month
If you are unable to eat or have severe food aversions
If you have additional dietary restrictions (allergies, religion, personal choices)

Warning Signs — When to Contact a Doctor IMMEDIATELY

Don’t hesitate — contact your oncologist or go to the emergency room if:

🚨 Fever over 100°F (38°C) — even without other symptoms. This may indicate a severe infection in the context of compromised immunity. Don’t wait to see if it “goes away.”

🚨 Severe difficulty breathing or oxygen saturation below 90% — medical emergency.

🚨 Chest pain, intense palpitations, irregular heartbeat — contact us urgently.

🚨 Uncontrolled vomiting for more than 24 hours or complete inability to drink fluids — the risk of dehydration is real.

🚨 Unusual bleeding — blood in urine, stool, vomit; nosebleeds/gums; unexplained heavy bruising.

🚨 Confusion, disorientation, convulsions — urgently to the hospital.

🚨 Sudden weakness of an arm/leg, sudden difficulty speaking — possible signs of stroke.

🚨 Diarrhea with more than 7 stools per day or severe dehydration — urgent.

🚨 Persistent cough, progressive shortness of breath — should be evaluated.

🚨 Blood in the urine — contact your doctor immediately.

Regular Monitoring — Don’t Neglect Analytics

The medical team will periodically monitor:

Complete blood count — the number of white blood cells, red blood cells, and platelets
Liver function — transaminases, bilirubin
Renal function — creatinine, urea
Electrolytes — sodium, potassium, magnesium
Cardiac markers — if medications are cardiotoxic
Respiratory function tests — if medications have a pulmonary risk

These tests are not bureaucracy—they are the early warning system that protects vital organs while treatment fights the cancer.

How to Best Protect Yourself During Treatment

Do ALL recommended assessments before starting treatment — cardiac, pulmonary, renal. It helps the team tailor treatment to you.
Follow the monitoring schedule — blood tests, ultrasounds, ECGs at set intervals. Don’t skip these visits.
Vaccinations as recommended by your doctor — flu, pneumococcus, other vaccines to reduce infections.
Report ANY new symptoms — fever, shortness of breath, chest pain, bleeding, confusion, tingling, extreme fatigue. Your doctor needs to know.
Do not interrupt or modify the treatment yourself — even if the effects are difficult, the doctor has other options: dose reduction, drug change, strategic breaks.
Regular moderate physical activity — helps reduce fatigue, depression, and constipation. 30 minutes of walking a day is enough.
Regular, quality sleep — going to bed and waking up at fixed times.
Psychological support — talking to a psychologist, families, support groups. The emotional aspect is an important part of recovery.

Summary — 10 Principles to Remember

Side effects are predictable — inform yourself in advance so you are prepared.
Severity matters — communicate exactly how it affects your daily life.
Early communication prevents escalation — don’t wait until symptoms become severe.
Don’t stop treatment on your own — even if the effects are difficult, your doctor has alternatives.
Nutrition and hydration are therapeutic weapons — use them strategically.
Moderate physical activity and regular sleep help — don’t stay inactive.
Fever above 38°C after treatment is an EMERGENCY — do not ignore.
Regular analysis is your shield — don’t skip monitoring.
Psychological and family support matters — don’t try to do this alone.
You are a partner in treatment, not just a patient —your understanding and active involvement make a difference.

Final Thoughts

Navigating complex cancer treatment is challenging, but knowing the potential side effects ahead of time helps you quickly recognize warning signs and take action. This can make the difference between a manageable complication and a serious one.

Your healthcare team is your partner in this fight. Honest communication, transparency about your symptoms, and close collaboration will help make treatment as effective and well-tolerated as possible.

You are not alone. There is medicine, family, psychological support, and communities of patients going through the same experience.

⚠️ Final Disclaimer: The information in this guide is for informational and educational purposes only. It does not constitute medical advice and does not replace the consultation of an oncologist. For diagnosis, treatment or interpretation of tests, always contact your medical team. . In case of a medical emergency, contact emergency services immediately ( call an ambulance immediately or go to the nearest emergency room) or the medical team that is following your treatment.

Bibliography

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Haanen J, et al. Management of toxicities from immunotherapy: ESMO Clinical Practice Guidelines. Annals of Oncology. 2022;33(12):1217–1246. two: 10.1016/j.annonc.2022.10.001
Lyon AR, et al. 2022 ESC Guidelines on Cardio-Oncology. European Heart Journal. 2022;43(41):4229–4361. two: 10.1093/eurheartj/ehac244
Loprinzi CL, et al. Prevention and Management of Chemotherapy-Induced Peripheral Neuropathy in Survivors of Adult Cancers: ASCO Guideline Update. Journal of Clinical Oncology. 2020;38(28):3325–3348. two: 10.1200/JCO.20.01399
Brown PD, et al. Memantine for the prevention of cognitive dysfunction in patients receiving whole-brain radiotherapy: a randomized, double-blind, placebo-controlled trial. Journal of Clinical Oncology. 2020;38(10):1019–1029. two: 10.1200/JCO.19.01767
Halperin EC, et al. Principles and Practice of Radiation Oncology. 7th ed. Wolters Kluwer; 2019. ISBN: 978-1496386793
National Cancer Institute. Common Terminology Criteria for Adverse Events — CTCAE, Version 5.0. US Department of Health and Human Services; 2017.

Dr. Onisim Florin Senior Medical Oncologist Founder of OncoExpertAI

Onisim Florin

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