Why does stress affect us so deeply? What science tells us

A racing heart before public speaking. A tight throat when faced with an unexpected situation. Thoughts looping endlessly at bedtime. Stress is not merely a psychological feeling, it is deeply embedded in the body. Every tension, every surge of anxiety, every state of alert relies on precise biological mechanisms. According to an OpinionWay barometer conducted for the Ramsay Health Foundation in 2025, nearly 6 out of 10 people in France report experiencing stress regularly. How does the physiology of stress work? By understanding the mechanisms of anxiety, it becomes easier to soothe it.

What is stress?

If stress is so difficult to define, it’s partly due to its variability between individuals. We use the term both to describe an external aggression, “this noise is stressful”, and to qualify our own state, “I am stressed”.

The Society for Neurosciences refers to a definition of stress adopted by specialists as:

“any external stimulus that threatens our homeostasis, that is, the normal balance of our bodily functions”.

In other words, stress arises as soon as the brain perceives a potential imbalance: constraint, overload, uncertainty, emotional pressure, real or imagined danger.

The French Foundation for Brain Research specifies that stress involves three inseparable dimensions:

• a stressor (event, situation, constraint, etc.);
• a physiological response;
• a subjective perception of the situation by the individual.

The brain constantly evaluates two essential dimensions: the valence of the stimulus (is it dangerous or not?) and the sense of control (do I have the resources to cope with it?).

This explains why two people exposed to the same event can react in completely opposite ways. The brain doesn’t respond solely to objective reality, but to how that reality is interpreted.

A survival response… that can become a problem

Discovered in 1936, Dr Hans Selye, an endocrinologist at the Institute of Experimental Medicine and Surgery of the University of Montreal, described the general adaptation syndrome in three phases:

• an alarm phase;
• a resistance phase;
• an exhaustion phase.

This model helps to understand how a response that is initially protective can, when prolonged, become harmful.

1. Acute adaptation: the body switches to alert mode

Faced with sudden danger, harsh braking while driving, an unexpected noise in the street or a professional emergency, the brain instantly triggers an automatic reaction.

The adrenal glands release catecholamines, including adrenaline and noradrenaline. Within seconds, the body prepares to act: heart rate accelerates, breathing becomes faster, and attention focuses on the threat.

This alarm phase is brief and effective. It allows rapid reaction, increased performance and responsiveness.

2. Stress persists: the body enters the resistance phase

When the stressful situation continues, the body seeks to maintain balance while remaining mobilised against the aggression. The physiological mechanisms of stress continue to manifest, but at a more sustained level.

New hormones come into play, such as glucocorticoids, including cortisol. Their role is to increase blood sugar levels in order to provide energy to the muscles, heart and brain.

The body remains on guard, sometimes for weeks or even months. It continues to function at the cost of a constant physiological effort.

3. The body is overwhelmed: exhaustion sets in

When exposure to stress becomes too long or too frequent, adaptive mechanisms run out of steam. Energy reserves decline, recovery becomes insufficient and imbalances take hold. Activating hormones overwhelm the body.

The French National Institute for Research and Safety for the Prevention of Occupational Accidents and Diseases (INRS) highlights that this situation promotes the onset of:

• persistent fatigue;
• sleep and concentration disorders;
• irritability;
• weakening of the immune system.

At this stage, stress ceases to be adaptive and becomes a risk factor for health.

Stress mechanisms: the two key circuits

The sympatho-adrenal axis (SAM)

In stress physiology, the first circuit activated mobilises the sympathetic nervous system and the adrenal medulla. This mechanism, known as the sympatho-adrenomedullary system (SAM), triggers the immediate release of adrenaline and noradrenaline, leading to:

• increased heart rate;
• increased blood pressure;
• rapid mobilisation of glucose;
• heightened alertness.

This mechanism acts within seconds and prepares the body for immediate action.

The hypothalamic-pituitary-adrenal axis

The second circuit, slower, is based on a hormonal cascade involving:

• the hypothalamus;
• the pituitary gland;
• the adrenal glands.

The hypothalamic-pituitary-adrenal axis forms the endocrine backbone of stress. This system leads to the release of cortisol, the central stress hormone, in order to:

• maintain energy availability;
• modulate inflammation;
• influence memory and attention.

It also plays a regulatory role through a feedback mechanism intended to restore balance once the threat has passed.

From brain to hormones: how stress reprogrammes our reactions

When we are confronted with stimuli, several areas of the brain are activated, particularly those involved in emotions and coordination:

• the amygdala, close to the hippocampus, represents the core of our alarm system. It plays a role in recognising our emotions and activating our response;
• the hippocampus contributes to mood regulation and our adaptation to the environment;
• the prefrontal cortex is responsible for decision-making.

According to the French Brain Research Foundation, chronic stress disrupts communication between these structures. The amygdala becomes more reactive, while the regulatory capacities of the prefrontal cortex diminish. Faced with prolonged stress, emotional reactions become more intense and gaining perspective becomes more difficult.

Chronic stress: when adaptation turns into biological wear and tear

When stress systems are repeatedly activated, this is referred to as biological wear and tear, sometimes called allostatic load, which manifests as:

• pain (colic, headaches, joint and/or muscle pain, etc.);
• sleep, appetite and digestive disorders;
• sensations of breathlessness and tightness;
• sensitivity and nervousness;
• anxiety, sadness and crying spells;
• a sense of malaise;
• impaired concentration and initiative.

According to the INRS dossier on workplace stress, this situation increases the risk of health impairments that may become irreversible following chronic stress:

• cardiovascular diseases;
• metabolic syndromes;
• musculoskeletal disorders (MSDs);
• damage to mental health.

The problem, therefore, isn’t stress itself, but the absence of a return to balance.

Can stress be measured in the body? Biological markers at work

Stress leaves measurable traces, even though no single indicator is sufficient to quantify it on its own. The main approaches include:

• salivary cortisol, reflecting the activity of the HPA axis;
• heart rate and heart rate variability (HRV), indicators of the balance between the sympathetic and parasympathetic nervous systems;
• validated questionnaires used to assess the subjective perception of stress.

Researchers emphasise the need to combine biological, physiological and subjective data to understand stress in all its complexity.

💡 Can technology decode our emotions? We are attempting to find out through a scientific study that explores this question.

Therapeutic virtual reality: a lever to relieve the physiology of stress

Therapeutic virtual reality is part of a non-pharmacological approach aimed at promoting physiological regulation of stress.

It is based on several complementary mechanisms:

• multisensory immersion promoting attentional focus;
• calming environments reducing hypervigilance;
• breathing exercises and cardiac coherence encouraging activation of the parasympathetic system.

The Healthy Mind solution offers configurable virtual reality sessions designed to help the body return to a state of relaxation and calm. Without eliminating sources of stress, this approach aims to support the body’s natural mechanisms for restoring balance. Several clinical studies on virtual reality already demonstrate the benefits of this approach.

Better understanding the physiology of stress makes it possible to act more appropriately, by supporting the body’s natural regulatory mechanisms. From this perspective, non-pharmacological approaches, such as therapeutic virtual reality, promote soothing and a return to physiological balance. If you would like to learn more about our system or try it for yourself, we would be delighted to offer you a demonstration.

References :

• Canini F. Éléments de physiologie et de physiopathologie du stress. Rev Neuropsychol 2019 ; 11 (4) : 251-8 doi:10.1684/nrp.2019.0520.
• Société des Neurosciences, Fiches Cerveau – Le stress, 2020.
• Dossier INRS, Stress au travail. Effets sur la santé, 2023.
• Fondation pour la Recherche sur le Cerveau, Le stress.
• Inserm, Quand le stress affaiblit les défenses immunitaires, 2020.
• Jacque, Claude ; Thurin, Jean-Michel ; Stress, immunité et physiologie du système nerveux, Med Sci (Paris), 2002, Vol. 18, N° 11; p. 1160-1166 ; DOI : 10.1051/medsci/200218111160.