Allostasia

Allostasia, often termed allostasis, is the process by which an organism maintains stability through change. It describes how physiological systems adjust their set points and response patterns in anticipation of and in response to environmental demands, rather than simply returning to a single fixed baseline.

Mechanistically, allostatic regulation is centered in the brain, which integrates sensory input, memory, and context to forecast needs and coordinate responses. It involves the autonomic nervous system, the hypothalamic-pituitary-adrenal axis, and interconnected neuroendocrine and immune pathways. Mediators such as cortisol, catecholamines, and inflammatory signals act to mobilize energy, alter metabolism, and modify bodily functions as needed.

Allostatic load refers to the cumulative physiological burden that arises from repeated or sustained activation of allostatic systems. Chronic stress, social adversity, sleep disruption, and unhealthy behaviors can contribute to elevated cardiovascular, metabolic, immune, and neuroendocrine activity over time, increasing disease risk and reducing resilience.

Distinction from homeostasis is central to the concept: homeostasis describes maintenance of a stable internal state around fixed set points, whereas allostasis emphasizes adaptive change and predictive regulation to meet changing demands. The framework has been applied across neuroscience, psychology, physiology, and medicine to understand how stress and experience shape health, aging, and disease trajectories.

History and reception: the term allostasis was introduced by Sterling and Eyer in 1988. While widely influential, some criticisms note conceptual ambiguities and overlap with traditional homeostatic ideas, and that measuring an “allostatic state” can be challenging. Nonetheless, the concept remains a useful lens for examining how the body sustains function through dynamic, anticipatory regulation.