Both therapies work by killing cells that divide rapidly, like cancer cells. Most cells divide more slowly, and so aren’t affected much. But some areas—like hair follicles, the digestive tract, skin, and bone marrow—are constantly regenerating. That means they have rapidly multiplying cells, which makes them susceptible to cancer therapies. Those areas are consequently subject to the most familiar chemo side effects: hair loss, digestive problems, dry or itchy skin, and immunodeficiency (since immune cells are made inside bone marrow).