What Is Psychoneuroimmunology-And How Does It Impact You?

The science behind the communication pathways between your nervous system, immune system, and mind - and what that means for your health.

When every system is talking at once

You push through a massive week at work, hold everything together through the stress of it all, and then the moment you finally sit down to rest… you get sick. You notice that when you're anxious for weeks on end, your digestion falls apart. Your skin flares up every time life gets overwhelming.

These patterns aren't coincidental. And they're far more than "just stress."

They're your body demonstrating, in real time, how deeply your nervous system, your immune system, and your psychological state are woven together.

This is the territory I work in each week in clinic, and it's the reason I'm currently completing a Masters in Clinical Psychoneuroimmunology. The deeper I go into this field, the more it confirms what I've been seeing with clients for years and more importantly, the more tools it gives me to help people in ways that conventional approaches often miss. The science that underpins all of this has a name.

PNI at a glance

The word itself tells you exactly what this field encompasses.

Psycho: your mind. Your thoughts, emotions, beliefs, and lived experiences.

Neuro: your nervous system. The brain, spinal cord, vagus nerve, and the entire network that governs how your body responds to the world.

Immunology: your immune system. The sophisticated defence network that protects you, repairs you, and when things go wrong, can turn against you.

PNI is the study of how these three systems communicate with each other. Not in isolation, not as separate departments that occasionally send memos, but as a deeply interconnected web of signals that are in constant, real-time conversation.

The endocrine system (your hormonal network, including the thyroid, adrenals, ovaries, and pancreas) is so deeply embedded in this conversation that some researchers use the expanded term PNEI (psychoneuroendocrinoimmunology). Hormones like cortisol, oestrogen, thyroid hormones, and insulin don't just regulate their own domains; they directly modulate immune function, influence neurotransmitter activity, and shift the nervous system's baseline between states of alertness and rest. When the endocrine system is dysregulated, as it so often is in perimenopause, thyroid conditions, adrenal dysfunction, or metabolic stress, the effects ripple through every other system. It's all one conversation.

What drew me to PNI, and what continues to drive my clinical work, is that it provides the scientific framework for something wholistic practitioners have observed for centuries: you cannot separate the mind from the body. They are one system.

Why this changes the clinical conversation

Conventional healthcare tends toward a compartmentalised model. You see a GP for your physical symptoms, a psychologist for your mental health, a gastroenterologist for your gut, and an immunologist for your immune system. Each specialist focuses on their piece.

But PNI reveals that these systems don't operate in silos. They share the same chemical messengers. They respond to the same signals. What happens in one system ripples through the others.

In clinical terms, this plays out in some important ways:

Chronic psychological stress does far more than generate a feeling of anxiety. It activates the hypothalamic-pituitary-adrenal (HPA) axis, floods the body with cortisol, and over time suppresses the very immune cells needed to stay well. This is the mechanism behind catching every cold going around during periods of burnout.

Unresolved trauma impacts the body profoundly, but the mechanism may be different from how popular culture has framed it. For years, the dominant narrative has been that trauma is physically stored in the body's tissues, locked in the muscles, the fascia, the organs. It's a compelling metaphor, and one that resonated with millions of people through Bessel van der Kolk's The Body Keeps the Score. But it's worth noting that somatic storage was always more metaphor than established mechanism. There has never been strong evidence for trauma literally residing in tissue.

A theoretical paper published this month in Frontiers in Systems Neuroscience (Kotler, Mannino, Fox & Friston, 2026) offers an alternative model that I find clinically compelling. The researchers, including Karl Friston, one of the most influential neuroscientists working today and the architect of the predictive coding framework, propose that trauma disrupts the brain's prediction systems, creating rigid, threat-biased patterns where the nervous system begins predicting the present and future through the lens of unresolved danger.

This is a theoretical framework, not a clinical trial. It hasn't been empirically tested yet. But it's built on decades of established predictive coding research, and it offers a more mechanistically coherent explanation for what we observe in practice.

What does this look like? The body is absolutely part of the conversation. Bodily signals like a racing heart, tight chest, or churning gut feed into the brain's predictive machinery and shape

what the person expects, fears, avoids, or interprets as dangerous. But in this model, the body is acting as a messenger, not an archive. Trauma creates a state where the nervous system loses its flexibility, becoming locked in hypervigilance, which then drives chronic low-grade inflammation. That inflammation can manifest as autoimmune flares, gut dysfunction, skin conditions, fatigue, and pain that doesn't have a clear structural explanation.

What I find most valuable about this reframe is what it means for recovery. If trauma is something buried inside the body that must be located and extracted, the process can feel disempowering. But if trauma is understood as a maladaptive prediction pattern, one that can be retrained, then there are far more actionable pathways forward. Bodywork, breathwork, somatic therapies, and movement still play a vital role, but the mechanism may be that they help create what the researchers call "prediction errors." These are moments that allow the nervous system to update its threat models and learn that safety is possible. This aligns closely with what I see in clinic every day, and it's an evolving area of research I'll be following closely.

Gut health extends well beyond digestion. The gut houses around 70% of the body's immune tissue and produces neurotransmitters like serotonin that directly influence mood, stress response, and emotional regulation. When the gut is compromised, the ripple effects touch every system.

This is why, in my clinical work, I never treat a symptom in isolation. If someone comes to me with recurrent infections, I'm also asking about their stress levels, their sleep, their emotional landscape, and their nervous system patterns. Because that's where the real drivers often live.

Everything is connected to everything

One of the most important principles PNI reinforces is that the body doesn't have neat, separate compartments. Everything is connected to everything, often through pathways that only become visible when you know where to look.

Here's one amazing example that stands out and I often discuss in clinic because it illustrates this interconnectedness so clearly: a bacterial infection in your mouth can contribute to a bulging disc in your spine. How? Certain oral bacteria, particularly an organism called Propionibacterium acnes which is a normal part of the mouth's microbiome, can enter the bloodstream during something as routine as a dental procedure, or even vigorous brushing when you have gum disease. Once those bacteria are circulating in the blood, they need resources to survive, and one of the things they exploit is free iron floating around in the system. That latent free iron essentially fuels them as they travel.

Now, your intervertebral discs are avascular. They have very little blood supply, which makes them a low-oxygen environment. For an anaerobic bacterium like P. acnes, that's actually an ideal place to set up camp. Research has found this bacterium present in a significant proportion of herniated disc tissue removed during surgery. Once it colonises the disc, it can trigger chronic low-grade inflammation (Modic changes on MRI) and contribute to disc degeneration and pain over time.

So the person presenting with chronic back pain and a disc bulge? Part of the root cause might trace back to an unresolved oral infection months or even years earlier. This is why I take such detailed case histories. This is why I ask about dental health, past infections, and seemingly unrelated symptoms. Because in the body, nothing is truly unrelated. It's all one interconnected system, and PNI gives us the framework to see those connections clearly.

The key players in this conversation

These are the primary pathways through which the mind-body conversation operates.

The HPA axis is your central stress response system. When your brain perceives a threat, whether it's a near-miss on the highway or a looming deadline, the hypothalamus signals the pituitary gland, which signals the adrenal glands to release cortisol. Short-term, this is protective. Long-term, it becomes one of the most significant drivers of immune suppression and systemic inflammation.

The vagus nerve is the longest cranial nerve in your body and acts as a direct communication line between your brain and your organs: your heart, lungs, gut, and immune tissue. When your vagus nerve has good tone (meaning it's functioning well), it helps keep inflammation in check and supports your body's ability to shift from a stress state into a healing state. This is a big part of why I use HRV biofeedback in clinic. It gives us a real-time window into how well this system is functioning.

Cytokines are chemical messengers produced by your immune cells. Some are pro-inflammatory (they ramp up the immune response) and some are anti-inflammatory (they calm it down). Chronic stress shifts the balance toward pro-inflammatory cytokines, which is one of the mechanisms behind the connection between long-term stress and conditions like autoimmunity, cardiovascular disease, and depression.

Neurotransmitters such as serotonin, dopamine, GABA, and noradrenaline are produced and active throughout the body, not only in the brain. They operate in the gut, the immune tissue, and the nervous system simultaneously, influencing everything from mood to immune cell activity. This is one of the clearest demonstrations of why mental health and physical health are the same conversation.

The endocannabinoid system (ECS) deserves particular attention here, because it's emerging as one of the most significant communication networks in the entire PNI picture. While the word "cannabinoid" often brings cannabis to mind, this is your body's own endogenous system. Your body produces its own cannabinoids (called endocannabinoids), and they act through receptors found on virtually every type of cell: neurons, immune cells, gut cells, and more. The ECS sits at the crossroads of the nervous system, the immune system, and the gut, helping to maintain balance across all of them. Researchers have described endocannabinoids as "master regulators" of the innate-adaptive immune axis, which speaks to just how central this system is to overall homeostasis.

What makes the ECS particularly fascinating from a PNI perspective is that it uses retrograde signalling. Most signalling in the body moves in one direction, from one nerve cell to the next, like passing a baton in a relay. But the endocannabinoid system can signal backwards. When a receiving cell is being overstimulated, it produces endocannabinoids that travel back to the sending cell and say "ease off." It's a built-in feedback mechanism that allows your body to fine-tune its own responses in real time, dialling inflammation up or down, modulating pain, regulating mood, and protecting neurons from being overwhelmed. This bidirectional communication is one of the reasons the ECS is so fundamental to how the nervous and immune systems stay in conversation with each other.

Bringing it together

For anyone navigating a complex health picture, where multiple things are going on and none of them quite make sense in isolation, PNI offers a unifying lens.

It explains why an autoimmune condition flares during periods of high stress. Why the gut plays up alongside anxiety. Why fatigue persists in ways that sleep alone doesn't resolve. Why someone can eat well and exercise regularly and still not feel well.

It also explains why approaches that address only one piece of the puzzle (only the diet, only the supplements, only the mindset work) sometimes fall short. Because the conversation between these systems is happening whether we acknowledge it or not. And the most effective approach is one that speaks to all of them.

How PNI and naturopathy come together

People sometimes ask me whether PNI and naturopathic medicine are the same thing. They're deeply complementary, but they come from different directions and meet in the middle.

Naturopathic philosophy has held for over a century that the body is a self-healing, interconnected whole. That you treat the cause, not the symptom. That the mind and body are inseparable. These principles, including vis medicatrix naturae(the healing power of nature) and tolle causam (treat the cause), have guided wholistic practitioners long before we had the tools to measure what was happening at a cellular level.

PNI arrived later and provided the biochemical evidence for why those principles work. When naturopathy says the body has an innate capacity to heal, PNI can point to the specific pathways: vagal tone restoring anti-inflammatory balance, endocannabinoid signalling maintaining homeostasis, the HPA axis recalibrating once the stressor is removed. The philosophy was right. PNI explains the mechanism.

But they aren't identical. PNI is a research discipline. It describes and measures what's happening between the nervous, immune, and endocrine systems. Naturopathy is a clinical practice with a treatment toolkit (herbal medicine, nutrition, lifestyle, bodywork, counselling) and guiding principles that inform how that toolkit is applied. It also encompasses areas that aren't strictly PNI territory, like constitutional prescribing, hydrotherapy, or nutritional biochemistry as standalone interventions.

What excites me is the bridge between the two. Naturopaths understand that stress affects the immune system...through the PNI lens, we can see how. That combination of traditional clinical wisdom with contemporary systems biology is what shapes my practice.

In a clinical session, that might look like combining adaptogenic and nervine herbs to support a dysregulated nervous system, while also using HRV biofeedback to help the client actually see and shift their stress patterns in real time. Or it might mean addressing gut health alongside emotional wellbeing, because in that person's body, the two are inseparable. The naturopathic toolkit provides the interventions. PNI provides the map of why and where to apply them.

Everything I'm learning in my study reinforces what I see in clinic every week: when we treat the person as a whole, when we honour the conversation between these systems instead of trying to silence individual symptoms, that's when real, lasting change happens.

Where to from here

This is the first in a series of journal posts where I'll be exploring the themes at the heart of my clinical work.

If this approach resonates with how you think about your own health, or if you've been looking for a practitioner who treats the whole picture rather than isolated symptoms, I'd love to work with you.

You can book a naturopathic consultation here or reach out if you'd like to chat about whether my approach is the right fit.

Rach xx