The evolution of the concept of stress and the framework of the stress system

Abstract

Stress is a central concept in biology and has now been widely used in psychological, physiological, social, and even environmental fields. However, the concept of stress was cross-utilized to refer to different elements of the stress system including stressful stimulus, stressor, stress response, and stress effect. Here, we summarized the evolution of the concept of stress and the framework of the stress system. We find although the concept of stress is developed from Selye's "general adaptation syndrome", it has now expanded and evolved significantly. Stress is now defined as a state of homeostasis being challenged, including both system stress and local stress. A specific stressor may potentially bring about specific local stress, while the intensity of stress beyond a threshold may commonly activate the hypothalamic-pituitary-adrenal axis and result in a systematic stress response. The framework of the stress system indicates that stress includes three types: sustress (inadequate stress), eustress (good stress), and distress (bad stress). Both sustress and distress might impair normal physiological functions and even lead to pathological conditions, while eustress might benefit health through hormesis-induced optimization of homeostasis. Therefore, an optimal stress level is essential for building biological shields to guarantee normal life processes.

Keywords: concept; definition; distress; eustress; homeostasis; stress; sustress.

Figure 1. FIGURE 1: The evolution of the framework of the stress system.

(A) The basic framework of the stress system. (B) The developing framework of the stress system. (C) The mature framework of the stress system.

Box 1. Box 1 Stress-related concepts

Figure 2. FIGURE 2: Homeostasis and allostasis.

Blue solid line represents the baseline, orange line represents dynamic equilibrium, and blue dot line represents the boundary of dynamic equilibrium.