Chemotherapy Toxicity

Why chemotherapy causes side effects

Most chemotherapy drugs attack cells that divide quickly. Cancer cells divide quickly, but so do healthy cells in the:

• bone marrow, which makes blood cells
• lining of the mouth and gut
• hair follicles
• skin and nails
• reproductive organs

Some drugs also have specific toxic effects on particular organs. Toxicity is graded from 1 (mild) to 5 (death) using the US National Cancer Institute's CTCAE system, which guides dose changes.

Common side effects

Low blood counts (myelosuppression)

• Low white cells (neutropenia): raises infection risk, usually lowest 7 to 14 days after treatment (the "nadir")
• Low red cells (anemia): tiredness, breathlessness, pale skin
• Low platelets (thrombocytopenia): bruising, nosebleeds, bleeding gums

Nausea and vomiting

Can start within hours (acute) or 2 to 5 days later (delayed). Modern anti-sickness medicines, used preventively, control most of it.

Mouth sores (mucositis)

Mucositis causes painful sores, redness and difficulty eating, usually 5 to 10 days after treatment.

Diarrhea and constipation

Diarrhea is common with drugs such as irinotecan and fluorouracil. Constipation often comes from anti-sickness medicines, opioids and vinca alkaloids.

Hair loss

Usually starts 2 to 4 weeks after the first treatment. It almost always grows back within 3 to 6 months after treatment ends, sometimes a different texture or color. Scalp cooling reduces hair loss with some regimens.

Fatigue

The most common side effect, often building through treatment and lasting months after.

Organ-specific toxicities

Tumor lysis syndrome

When chemotherapy rapidly kills large numbers of cancer cells, especially in leukemias and lymphomas, their contents flood the blood, causing high potassium, phosphate and uric acid, and kidney failure. It is prevented with fluids and medicines such as allopurinol or rasburicase. See tumor lysis syndrome.

Long-term and late effects

Heart damage, second cancers (such as leukemia years later), infertility, early menopause, bone thinning and persistent neuropathy can appear months to years after treatment. Survivorship clinics monitor for these.

Who is at higher risk

• older adults
• people with kidney, liver or heart disease
• poor nutrition or frailty
• genetic variations in drug metabolism, such as DPD deficiency, which can cause life-threatening toxicity from fluorouracil and capecitabine. Some centers test for it before treatment
• combinations of drugs and radiotherapy

Neutropenic fever: what to do

A fever during chemotherapy may be the only sign of a serious infection, because the body cannot mount its usual response.

• check your temperature if you feel unwell, hot, cold or shivery
• call your oncology team's emergency number or go to the ER if your temperature is 38 °C (100.4 °F) or higher
• tell staff you are having chemotherapy, so antibiotics are started within an hour
• do not take acetaminophen to bring the fever down before calling, as it can mask the fever

How toxicity is prevented and managed

• blood tests before each cycle to check counts, kidney and liver function
• dose adjustment or delay when counts are low or organs are affected
• growth factors (G-CSF injections) to boost white cell recovery
• anti-sickness medicines given before and after treatment
• mouth care: soft toothbrush, salt water or bicarbonate rinses, avoiding alcohol mouthwash
• heart monitoring with echocardiograms during anthracycline or trastuzumab treatment
• hearing tests with cisplatin
• fertility preservation (sperm banking, egg or embryo freezing) before treatment
• transfusions for severe anemia or low platelets

Tips for coping

• eat small, frequent meals and drink plenty of fluids
• rest, but stay gently active, which reduces fatigue
• wash hands often and avoid people with infections
• avoid raw or undercooked meat, eggs and unpasteurized dairy when counts are low
• protect skin from the sun
• keep a symptom diary and report problems early, before they become severe
• ask about vaccines: flu shots are recommended, but avoid live vaccines during treatment

Frequently asked questions

What are the most common side effects of chemotherapy?

Fatigue, nausea and vomiting, hair loss, mouth sores, diarrhea or constipation, loss of appetite, and low blood counts are the most common. Which ones you get depends on the specific drugs, doses and your health.

What is neutropenic fever?

It is a fever of 38 °C (100.4 °F) or higher in someone with a low white blood cell count, usually during chemotherapy. It can signal a life-threatening infection and needs antibiotics within an hour. Contact your cancer team immediately.

How long do chemotherapy side effects last?

Most, such as nausea, mouth sores and low counts, improve within days to weeks after each cycle. Hair grows back within months after treatment ends. Fatigue and neuropathy can last months or longer, and a few effects are permanent.

Can chemotherapy damage the heart or nerves permanently?

Yes, some drugs can. Anthracyclines can weaken the heart, and platinum drugs, taxanes and vincristine can cause lasting nerve damage. Monitoring and dose adjustments reduce the risk, and early reporting of symptoms helps.

How can I reduce chemotherapy side effects?

Take preventive medicines as prescribed, report symptoms early, eat and drink regularly, stay gently active, practice careful mouth and hand hygiene, and attend all blood tests. Your team can adjust doses or add supportive treatments.