Chemotherapy Complications and Side Effects

Why chemotherapy causes side effects

Chemotherapy drugs kill cells that divide quickly. Cancer cells divide fast, but so do cells in the bone marrow, the lining of the mouth and gut, hair follicles and reproductive organs. Damage to these normal cells causes most side effects. Different drugs have different patterns, and effects depend on the dose, schedule, combination and your overall health.

Many side effects follow a pattern: nausea in the first days after treatment, the lowest blood counts (the nadir) about 7 to 14 days after treatment, and recovery before the next cycle.

Common chemotherapy complications

Low blood counts and infection

• Neutropenia (low white blood cells): the most dangerous common complication. Infections can become serious within hours. Febrile neutropenia (fever with low neutrophils) is a medical emergency that needs IV antibiotics, ideally within an hour of arrival.
• Anemia (low red blood cells): tiredness, breathlessness and pale skin. See anemia due to malignancy.
• Thrombocytopenia (low platelets): easy bruising, small red spots on the skin, bleeding gums and nosebleeds.

Nausea and vomiting

Chemotherapy-induced nausea may start within hours (acute) or 1 to several days later (delayed). Modern preventive anti-sickness medicines, given before chemotherapy and taken on schedule afterward, prevent or control it in most people.

Fatigue

Cancer-related fatigue is very common, affects energy and concentration, and is not fully relieved by rest. Gentle regular exercise is one of the most effective treatments.

Mouth sores (mucositis)

Mucositis is inflammation and ulceration of the mouth and gut lining, causing pain, difficulty eating and sometimes infection. It usually begins 5 to 10 days after treatment.

Gut problems

Diarrhea (from drugs such as irinotecan and fluorouracil), constipation (often from anti-sickness medicines and opioids), loss of appetite, changes in taste and weight loss.

Hair loss

Many but not all drugs cause hair loss, usually starting 2 to 4 weeks after the first treatment. Hair usually regrows within 3 to 6 months after treatment ends. Scalp cooling can reduce hair loss with some regimens.

Skin and nail changes

Rashes, dryness, darkening, sensitivity to sun, hand-foot syndrome (red, painful palms and soles) and brittle nails.

Organ-specific complications

Other serious complications

• Tumor lysis syndrome: rapid breakdown of cancer cells releases potassium, phosphate and uric acid, which can cause kidney failure and dangerous heart rhythms. Most common with fast-growing blood cancers. Prevented with fluids and medicines.
• Blood clots: cancer and chemotherapy raise the risk of deep vein thrombosis and pulmonary embolism.
• Infusion reactions and allergic reactions during treatment.
• Extravasation: some drugs damage tissue if they leak out of a vein.
• Second cancers: a small long-term risk of leukemia and other cancers with some drugs.

How complications are monitored

Before each cycle, your team checks blood counts, kidney and liver function, and asks about side effects. Heart scans, hearing tests or lung function tests may be done for specific drugs. Keep a diary of symptoms and temperatures, and always have your cancer center's 24-hour contact number.

Prevention and management

• Anti-sickness medicines before and after treatment, taken on schedule rather than waiting for nausea.
• Growth factors (G-CSF injections) to boost white cell recovery in higher-risk regimens.
• Dose adjustments or delays when side effects are severe.
• Mouth care: a soft toothbrush, bland mouth rinses (salt and baking soda), and avoiding alcohol-based mouthwashes.
• Infection precautions: handwashing, food safety, avoiding sick contacts, and recommended inactivated vaccines (ask your team before any vaccine).
• Nutrition support: small frequent meals, fluids, and a dietitian referral if you lose weight.
• Exercise: walking and light strength training reduce fatigue.
• Neuropathy: report symptoms early so the team can adjust doses. Duloxetine may help painful neuropathy.
• Psychological support and help with the costs of care. See financial toxicity.

Long-term effects

Most side effects resolve within weeks to months of finishing treatment. Some can persist or appear years later, including neuropathy, heart problems, infertility, early menopause, cognitive changes, fatigue and second cancers. Survivorship care plans include follow-up for these risks.

Frequently asked questions

What are the most common side effects of chemotherapy?

The most common are tiredness, nausea and vomiting, low blood counts with a higher risk of infection, mouth sores, hair loss, diarrhea or constipation, loss of appetite and changes in taste. Which ones you get depends on the specific drugs, doses and your health.

Why is fever dangerous during chemotherapy?

Chemotherapy can lower white blood cells, which fight infection. With low counts, a minor infection can become life-threatening sepsis within hours. A temperature of 38 °C (100.4 °F) or higher needs immediate contact with your cancer team and usually urgent IV antibiotics.

When are side effects worst after chemotherapy?

Nausea is usually worst in the first few days. Blood counts are typically lowest about 7 to 14 days after treatment, when infection risk is highest. Mouth sores often appear after 5 to 10 days. Fatigue can build up over successive cycles.

Do chemotherapy side effects go away?

Most do, usually within weeks to a few months after treatment ends. Hair regrows, blood counts recover and energy improves. Some effects, such as nerve damage, heart damage, hearing loss and infertility, can be long-lasting, so ongoing follow-up is important.

Can chemotherapy side effects be prevented?

Many can be reduced. Preventive anti-sickness medicines control most nausea, growth factor injections lower infection risk, scalp cooling reduces hair loss with some drugs, and careful mouth care helps with mucositis. Reporting symptoms early allows your team to adjust treatment.