 Recent research suggests that reactive oxygen species, ROS, may function as signaling molecules to promote health and extend lifespan, rather than causing oxidative stress and aging. This concept, known as mitochondrial hormesis or mitohormesis, involves low dose ROS signaling events induced by calorie restriction, hypoxia, temperature stress, physical activity, insulin slash IGF1 receptors, ampipendent kinase, AMPK, target of rapamycin, TOR, and certuents, leading to improved systemic defense mechanisms, proteostasis. Unfolded protein response, UPR, stem cell maintenance, and stress resistance. However, interfering with these ROS signals through pharmacological or natural compounds may be harmful, as antioxidants have been found to be useless or even harmful. This article was authored by Michael Risto and Catherine Schmeisser.