In this article, we’re going to learn about mitohormesis, the activity of reactive oxygen species (ROS) as signaling molecules, and how and why ROS can be both beneficial and harmful. We will also discuss what leads to excessive ROS production and accumulation, how this associates with aging, and where antioxidants fit into the equation. Lastly, we’ll discuss nutritional strategies that can support the antioxidant defenses cells and mitochondria use to protect themselves against excessive ROS.