Each drug or combination of drugs may cause different side effects in different patients.

Chemotherapy has to be carefully timed and planned so that it harms the rapidly dividing unhealthy (cancerous) cells without causing too much damage to healthy cells that are also rapidly dividing. Healthy bone marrow and hair producing cells are also rapidly dividing as are the cells that make up the mucous lining of the intestinal tract. They too are affected by chemotherapy. Damage to these cells causes the three most common side effects of chemotherapy: nausea and vomiting, hair loss and bone-marrow depression. For this reason, doctors prescribe a combination of chemotherapy drugs, at high or low doses and at different times, creating an individual treatment plan for each child. The aim of this is to eliminate the cancer and minimize side effects associated with the drugs. Common side effects of chemotherapy may include:

	Low white blood cell count (neutropenia)
	Low red blood cell count (anemia)
	Hair loss (alopecia)
	Nausea and/or vomiting
	Diarrhea
	Mouth sores (mucositis)

Most chemotherapy drugs cause a temporary lowering of the blood cell counts, which results in a weakened immune system. Compromised immunity is one of the most serious side effects of chemotherapy. When these counts are low, children and teenagers with cancer are more susceptible to infection. They have more difficulty fighting certain infections and may bleed more easily and require transfusions with red blood cells or platelets. A child or teenager who develops a fever or major infection may be admitted to hospital for intravenous of antibiotic therapy.

Episodes of infection can interfere with the scheduling of treatment. Children and teenagers receiving chemotherapy are often given an antibiotic to help prevent infections. This is termed prophylaxis.