by Hazel Milla
When you hear the word “stress,” it likely brings to mind specific feelings and events. For example, you might remember a time you gave a presentation to a large crowd and your hands felt clammy while your heart beat rapidly. Physical responses like these are common when your stress response is activated. While it may be uncomfortable, the stress response evolved to help us address important tasks and respond to sources of danger. In excess and over long periods, however, stress can contribute to disease. This is an example of the mind-body connection, the idea that your mental state and physical health mutually affect each other. To varying extents, this concept has existed across history and cultures, with understanding of the mind-body connection influencing ancient Greek and traditional Chinese medicine practices, among others. Knowledge of the mind-body connection has expanded through the work of scientists throughout history and modern researchers.
Figure 1. Stress can contribute to the development and severity of many diseases, including diabetes, cardiovascular disease, depression, chronic obstructive pulmonary disease, immune disorders, inflammatory bowel disease, and more. Created in BioRender. Milla, H. (2026) https://BioRender.com/iif6tjj
The development of modern stress research
The word “stress” originated in the field of engineering, referring to the physical tension applied to a structure. Since then, the use of the word has expanded. Hans Selye (1907–1982) was one of the early researchers who popularized the term “stress” in medical vocabulary. Now, in medicine, stress is generally defined as a state ub which homeostasis is challenged. Homeostasis is the process by which the body maintains a steady internal state. This concept was initially developed by physiologist Claude Bernard (1813–1878) and later named by physiologist Walter Cannon (1871-1945) in 1926.
The cause of a challenge to homeostasis, referred to as a “stressor”, can affect the body or the mind. Scientists often refer to these stressors as physiological or psychological, respectively. Hans Selye observed that when rats were subjected to physiological stressors, they experienced symptoms independent of the physical damage caused by those stressors. The symptoms were also nonspecific to the type of stressor. Selye would eventually term this set of symptoms General Adaptation Syndrome (GAS) and, eventually, the “stress response,” which consists of three stages (Figure 1). The first stage, called the “alarm reaction,” is characterized by the body preparing to fight or flee. In the second stage, termed “resistance,” the body adapts to the stressor. For example, the body becomes tired in response to sustained hunger, requiring less energy to function. In the final stage, “exhaustion,” the system becomes too worn out to sustain the response against the stressor. From studying the stress response and its various stages, Selye identified that excessive stress over long stretches of time can result in disease, such as stomach ulcers.
Figure 2. Resistance to stress during the three stages of General Adaptation Syndrome (GAS). Image source.
In 1984, the psychologists Richard Lazarus and Susan Folkman elaborated on Selye’s notions about the stress response by proposing that how we perceive and respond to stressors can affect the degree to which those stressors contribute to disease. Then, in 1988, Peter Sterling and Joseph Eyer coined the term allostasis, referring to the process by which the body adapts to stressors to maintain homeostasis. Bruce McEwen further developed the concept of allostatic load, which refers to wear and tear on the body from the process of adapting to prolonged stress.
The present and future of stress research
The scientists previously mentioned are just some of the many important figures in the history of stress research. Today, researchers continue to investigate the ways stress can negatively impact health and how this occurs. In recent years, researchers have made strides in studying the intergenerational effects of stress–in other words, how stress in one generation can be passed down to offspring.
One increasingly common way to explore the impacts of stress is through the study of epigenetics. Epigenetics are changes made in the body that alter gene expression, which is how information encoded in DNA is converted into biological functions. These modifications provide a useful lens through which researchers can assess gene-environment interactions, or the interplay between a person’s specific genes and the environmental factors to which they are exposed. By investigating these modifications, scientists are further uncovering the impact of stress on biological processes leading to disease.
Based on the history of stress research, it’s clear that something as seemingly straightforward as feeling stressed can be layered with complexity. Even the word “stress” has evolved over generations from its original meaning in engineering to its current meaning as a biological concept. Today, there is still a lot of ambiguity around the term “stress,” but, as scientists, by starting with its definition as a disruption of homeostasis, we can better pinpoint what’s happening in the body when we become stressed. With a sufficient understanding, we may one day learn how to reverse the harm caused by excessive stress and ultimately improve public health outcomes.
