Adaptation in the face of stressful situations and stimuli involves activation of neural, neuroendocrine and neuroendocrine-immune mechanisms. This adaptation has been called "allostasis" or "maintaining stability through change", which is an essential component of maintaining homeostasis. The main downstream hormones produced as a result of the stress response, cortisol and epinephrine (adrenaline), have beneficial effects on the body that can become detrimental with excessive activation, such as increased blood pressure and heart rate.

The physiological responses involved in the stress response are widely considered adaptive as they are effective at responding to acute threats to survival across many species. However, in environments of chronic or frequent activation of the stress response, such as exposure to violence or trauma, poverty, war, hypoxia, or low rank in a social hierarchy, the stress response constantly disrupts homeostasis resulting in overexertion of physiological systems.

Allostatic load can be measured in physiological systems as chemical imbalances in autonomic nervous system, central nervous system, neuroendocrine, and immune systemactivity as well as perturbations in the diurnal rhythms, and, in some cases, plasticity changes to brain structures."