Why does chemotherapy cause easy bleeding and bruising?

Some cancer treatments, such as chemotherapy and targeted therapy, can increase your risk of bleeding and bruising because they can lower the number of platelets in the blood. Platelets are the cells that help your blood clot and stop bleeding.

When your platelet count is low, you may bruise or bleed a lot or very easily and may see tiny purple or red spots on your skin. This condition is called thrombocytopenia. It's important to tell your doctor or nurse if you notice any of these changes.

Some bleeding problems need a call right away—such as bleeding that doesn't stop after a few minutes, bleeding from your mouth or nose, red or pink urine, black or bloody stools, or head and vision changes like bad headaches, confusion, or feeling very sleepy. Your healthcare team can explain steps to lower your risk and tell you which signs mean you should call them or go to the emergency room.