Hormetic

Hormetic is an adjective relating to hormesis, a dose–response phenomenon in which a low exposure to a potentially harmful stressor induces a beneficial adaptive response, while higher exposures are detrimental. The core idea is that the effect of a stressor is not simply linear; at low doses, systems adapt in ways that improve function or resilience, whereas large doses cause damage.

Typically the response is biphasic, producing stimulation at low doses and inhibition or harm at high doses. The resulting dose–response curve is described as J-shaped or U-shaped depending on the endpoint being measured. Stressors studied include toxins, radiation, heat, and caloric restriction, as well as physiological stresses such as exercise.

Biological mechanisms involve activation of cellular stress responses and maintenance pathways, including antioxidant defenses (often via Nrf2), DNA repair, autophagy, proteostasis, and mitochondrial quality control. Mild stress can upregulate protective programs that bolster resilience to subsequent challenges, a concept used in preconditioning strategies.

Evidence for hormesis appears in toxicology, pharmacology, and physiology, and practical examples include exercise-induced adaptations, caloric restriction or intermittent fasting, and certain phytochemicals that mimic stress. The applicability to humans remains a topic of debate, with questions about reproducibility, dose selection, and context.

Applications span risk assessment, the design of dosing regimens in pharmacology, and medical preconditioning to reduce injury from anticipated stressors. Critics caution that not all agents exhibit hormesis, effects can be highly context-dependent, and publication bias may influence reported benefits.

Origin of the term derives from Greek to excite, with hormesis named for the stimulatory response observed at low doses.