 Cancer is a disease caused by abnormal growth of cells. It has been found that highly reactive molecules known as reactive oxygen species, iOS, can be used to kill cancer cells. These molecules are naturally produced in small amounts in healthy cells, but when they are overproduced in cancer cells, they can cause them to die. This process is known as programmed cell death, and it can be used to selectively target diseased cells. By using drugs or light-stimulated therapies to increase the production of iOS, researchers believe this may lead to more effective treatments for cancer. This article was authored by Bruno Parillo, Masia Di Donotto, Antonio Pozzoni, and others.