The term “reactive oxygen species” (ROS) refers to a family of extremely reactive molecules. They are crucial as secondary messengers in both physiological functioning and the development of cancer. Tumors have developed the ability to survive at elevated ROS levels with significantly higher H2O2levels than normal tissues. Chemodynamic therapy is a novel approach to cancer treatment that generates highly toxic hydroxyl radicalsviaa Fenton/Fenton-like reaction between metals and peroxides. Inorganic nanoparticles cause cytotoxicity by releasing ROS. Inorganic nanoparticles can alter redox homoeostasis by generating ROS or diminishing scavenging mechanisms. Internalized nanoparticles generate ROS in biological systems independent of the route of internalisation. This method of producing ROS could be employed to kill cancer cells as a therapeutic strategy. ROS also play a role in regulating the development of normal stem cells, as excessive ROS disturb the stem cells' regular biological cycles. ROS treatment has a significant effect on normal cellular function. Mitochondrial ROS are at the centre of metabolic changes and control a variety of other cellular processes, which can lead to medication resistance in cancer patients. As a result, utilising ROS in therapeutic applications can be a double-edged sword that requires better understanding.