Stress and the Immune System: What Happens in the Body When You Live in a Constant State of Alert

Stress and the immune system are closely connected, even though we often don’t realize it.

Have you ever gone through a period of intense stress… and then gotten sick?

A cold.
A deep sense of fatigue.
Inflammation that flares up again.
A body that no longer seems to recover as it used to.

Many people perceive stress as something that only involves the mind.

But stress doesn’t stay in the mind.

When it lasts too long, it enters the body.
It interacts with the nervous system.
It alters hormones.
It influences inflammation.
And it can change the way the immune system responds.

Stress and the immune system: the link between brain, hormones, and defenses

The relationship between stress and the immune system is now one of the most studied topics in neuroscience.

The immune system does not work in isolation.
It is in constant communication with:

• the brain
• the nervous system
• stress hormones

Psychoneuroimmunology studies exactly this connection.

A meta-analysis by Segerstrom and Miller examined over 300 studies, showing that psychological stress is associated with real changes in immune parameters.

When we perceive a threat, the brain activates two main systems:

• the sympathetic nervous system
• the HPA axis (hypothalamus–pituitary–adrenal)

This leads to the production of cortisol.

Cortisol is not negative.
It helps mobilize energy and regulate inflammation.

The problem arises when stress becomes chronic.

Stress and the immune system: the difference between acute and chronic stress

Not all stress is harmful.

Acute stress (short-term)

• temporarily increases immune activity
• prepares the body to respond
• activates cells such as NK (natural killer) cells

It is an adaptive response.

Chronic stress (long-term)

• reduces the effectiveness of certain defenses
• increases inflammation
• makes the immune system less precise

Short-term stress can activate the immune system.
Chronic stress can confuse it.

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Chronic stress and inflammation: when the body loses balance

With prolonged stress, something more complex happens.

It’s not just about “lower defenses.”

A dysregulation occurs:

• less defense where it is needed
• more inflammation where it is not needed

Pro-inflammatory cytokines may remain active.
A state of low-grade chronic inflammation develops.

This condition is associated with:

• chronic fatigue
• increased vulnerability
• difficulty recovering

Stress and the immune system: cortisol and glucocorticoid resistance

Normally, cortisol helps turn off inflammation.

But in chronic stress, a phenomenon may occur called:

glucocorticoid resistance

Cells become less sensitive to cortisol.

The “calm down” signal is no longer effectively received.

The result:

• inflammation remains active
• the immune system loses regulation

It’s as if the system can no longer distinguish:

when to activate
when to stop

Stress and the immune system: why chronic stress affects health

The body does not always distinguish between:

• real danger
• perceived threat

Ongoing worries, difficult relationships, loneliness, financial pressure…
become repeated signals of alarm.

And the body responds.

Chronic stress can:

• disrupt sleep
• increase inflammation
• reduce the ability to recover
• influence behavior (eating, movement, social withdrawal)

The immune system as a “surveillance system”

Imagine the immune system as a security team.

If there is an emergency, it responds.

But if the alarm keeps going off continuously:

• the team becomes exhausted
• it overreacts or underreacts

Chronic stress is an alarm that never turns off.

Mindfulness and stress: changing the relationship with the alarm

Mindfulness does not eliminate stress.

But it can change the way we experience it.

If the body reacts not only to events but also to:

• repetitive thoughts
• anticipation
• interpretation

then becoming aware is essential.

A 2016 systematic review suggests that mindfulness meditation may influence:

• inflammation
• cellular immunity
• stress regulation

(although results are still being studied)

“Life only unfolds in moments”: the role of the present moment

As Jon Kabat-Zinn reminds us in Full Catastrophe Living:

“Life only unfolds in moments.”

Life does not happen all at once.
It unfolds moment by moment.

And it is in the present moment that we can interrupt, even for a few seconds, the ongoing activation of the internal alarm.

A simple practice to reduce stress

You don’t need to do anything complex.

You can start like this:

• feel your body
• notice your breath
• observe without judgment

Breathing in: I recognize tension
Breathing out: I let go

The body is not your enemy.
It is trying to protect you.

Conclusion: listening to the body before it has to shout

Chronic stress is often a body that has lost its rhythm.

Persistent fatigue.
Continuous tension.
Disturbed sleep.
A constant sense of being “on.”

Chronic stress can alter the immune system, increasing inflammation and reducing the body’s ability to recover.

The point is not to eliminate stress.

The point is to learn to listen to the body before it has to shout.

Mindfulness can become a way back.

Not an escape.
But a more conscious way of living.

This article explores the connection between stress and the immune system.
It shows how the body responds to a prolonged state of alert and is part of a series of articles specifically dedicated to the relationship between stress and the immune system in all its implications.

We created this series to explore the relationship between stress, mind, body, and the nervous system through neuroscience, and to explain how mindfulness can help, including practical approaches.

You can find the related video playlist on:

THE MINDFUL LAB

A space where:
Mindfulness · Neuroscience · Spirituality · Human Experience
come together.

If this article has helped you, share it using the buttons below the scientific references, explore more content on our YouTube channel, and continue your journey toward a more aware and less stressed mind by reading here.

Scientfic References:

  Suzanne C. Segerstrom & Gregory E. Miller (2004). Psychological stress and the human immune system: A meta-analytic study of 30 years of inquiry.
https://pubmed.ncbi.nlm.nih.gov/15250815/

  Psychological Bulletin (American Psychological Association) – versione PDF dello studio:
https://www.apa.org/pubs/journals/releases/bul-1304601.pdf

  Sheldon Cohen et al. (2012). Chronic stress, glucocorticoid receptor resistance, inflammation, and disease risk.
https://www.pnas.org/doi/10.1073/pnas.1118355109

  Stress and immune system communication pathways (HPA axis and sympathetic nervous system) – revisione scientifica:
https://pmc.ncbi.nlm.nih.gov/articles/PMC11546738/

  Mindfulness meditation and immune system / inflammation markers – systematic review (2016):
https://pmc.ncbi.nlm.nih.gov/articles/PMC4940234/

  Jon Kabat-Zinn (1990). Full Catastrophe Living: Using the Wisdom of Your Body and Mind to Face Stress, Pain, and Illness.
https://www.goodreads.com/work/quotes/16180-full-catastrophe-living-using-the-wisdom-of-your-body-and-mind-to-face