Hormesis is a concept in toxicology and biology where exposure to low doses of a substance can have beneficial effects, while high doses can be toxic. In biology and medicine, hormesis is defined as an adaptive response of cells and organisms to moderate stress, such as ischemic preconditioning, exercise, dietary energy restriction, and low doses of phytochemicals. Recent research has identified cellular signaling pathways and molecular mechanisms that mediate these responses, involving enzymes like kinases and deacetylases, and transcription factors like Nrf-2 and NF-kB. These pathways lead to the production of cytoprotective and restorative proteins, enhancing cellular resilience. Understanding these mechanisms is leading to novel approaches for preventing and treating various diseases. Hormesis is also integral to normal physiological functions, such as the activation of protective pathways in neurons exposed to excitatory neurotransmitters. The concept of hormesis is fundamental in evolutionary theory, as it helps organisms cope with environmental hazards. Biphasic dose-response curves, where low doses have beneficial effects and high doses are toxic, are common in many biological systems. Examples include ischemic preconditioning, where brief periods of mild ischemia protect against full-blown heart attacks or strokes. Hormesis is also observed in lifestyle factors like exercise, dietary energy restriction, and intellectual activities, which can protect against age-related diseases. Additionally, phytochemicals from fruits and vegetables exert beneficial effects by activating adaptive stress response pathways, contributing to their health benefits. The concept of hormesis is supported by historical observations and is implicated in the actions of drugs and complementary therapies.Hormesis is a concept in toxicology and biology where exposure to low doses of a substance can have beneficial effects, while high doses can be toxic. In biology and medicine, hormesis is defined as an adaptive response of cells and organisms to moderate stress, such as ischemic preconditioning, exercise, dietary energy restriction, and low doses of phytochemicals. Recent research has identified cellular signaling pathways and molecular mechanisms that mediate these responses, involving enzymes like kinases and deacetylases, and transcription factors like Nrf-2 and NF-kB. These pathways lead to the production of cytoprotective and restorative proteins, enhancing cellular resilience. Understanding these mechanisms is leading to novel approaches for preventing and treating various diseases. Hormesis is also integral to normal physiological functions, such as the activation of protective pathways in neurons exposed to excitatory neurotransmitters. The concept of hormesis is fundamental in evolutionary theory, as it helps organisms cope with environmental hazards. Biphasic dose-response curves, where low doses have beneficial effects and high doses are toxic, are common in many biological systems. Examples include ischemic preconditioning, where brief periods of mild ischemia protect against full-blown heart attacks or strokes. Hormesis is also observed in lifestyle factors like exercise, dietary energy restriction, and intellectual activities, which can protect against age-related diseases. Additionally, phytochemicals from fruits and vegetables exert beneficial effects by activating adaptive stress response pathways, contributing to their health benefits. The concept of hormesis is supported by historical observations and is implicated in the actions of drugs and complementary therapies.