Inflammation

• Brain fog
• Poor attention and concentration
• Poor memory
• Depression
• Mood swings
• Anxiety
• Poor sleep
• Addiction
• Exhaustion

• Aches and pains
• Stiffness (when joints and muscles are affected)
• Heat and swelling
• Redness
• Change in bowel movements (when digestion is affected)
• Headaches (common in chronic inflammation)

Neuro-inflammation can be caused by traumatic brain injuries (for example in a car accident) or are correlated with brain infections or autoimmune disease.

In these circumstances, activated central nervous system (CNS) immune cells and the blood-brain barrier (BBB) coordinate the production of cytokines — chemicals involved in inflammation, and other chemical messengers — which directly influence brain function and act on specific receptors of the brain.Theus, M.H., 2024. Neuroinflammation and acquired traumatic CNS injury: a mini review. Frontiers in Neurology, 15, p.1334847.

Neuro-inflammation is implicated in various psychiatric disorders such as:

• Depression
• Bipolar disorder
• Schizophrenia
• Obsessive-compulsive disorder
• Parkinson’s disease

Chronic neuro-inflammation, is implicated in neurodegenerative disease such as Alzheimer’s disease and declines in cognitive function.

There is strong evidence linking depression to inflammation, Paganin, W. and Signorini, S., 2024. Inflammatory biomarkers in depression: scoping review. BJPsych Open though it’s not clear whether inflammation contributes to depression, or whether depression contributes to inflammation.

• Studies demonstrate that, when compared to non-depressed patients, depressed patients consistently demonstrate all the cardinal features of inflammation Paganin, W. and Signorini, S., 2024. Inflammatory biomarkers in depression: scoping review. BJPsych Open.
• There is a strong association between inflammatory markers and individual depressive symptoms such as fatigue, cognitive dysfunction, and impaired sleep

Lypopolysaccharides (LPS) which are components of bacteria in the gut, are one of the major causes of inflammation. LPS can get into the bloodstream when there is leaky gut, and can cause systemic inflammation, where it can cause behavioural symptoms overlapping with those of major depression Ng, Q.X. et al., 2025. Leaky gut biomarkers as predictors of depression and suicidal risk: a systematic review and meta-analysis. Diagnostics, 15(13), p.1683.

There is also a link between depression, inflammation and oxidative pathways. Inflammation and oxidation are often seen as ‘essential partners’ in mental health issues.Vollbracht, C. and Werner, M., 2024. The role of inflammation and oxidative stress in the pathophysiology of depressions: time to consider vitamin C deficiency. Exploration of Neuroscience, 3, pp.287–294.

• Depression is associated with a chronic, low-grade inflammatory responseBouras, M. et al., 2024. Low-grade inflammation associated with major depression subtypes: a cross-sectional study. Brain Sciences. Hassamal, S., 2023. Chronic stress, neuroinflammation, and depression: an overview of pathophysiological mechanisms and emerging anti-inflammatories. Frontiers in Psychiatry.
• Depression is associated with elevated cytokines which mediate the body’s innate immunity and their receptors in blood and cerebrospinal fluid (CSF) Gigase, F.A.J., Smith, E., Collins, B., Moore, K., Snijders, G.J.L.J., Katz, D. et al., 2023. The association between inflammatory markers in blood and cerebrospinal fluid: a systematic review and meta-analysis. Molecular Psychiatry.
• There is a link between depression and premature mortality in chronic diseases such as cancer and heart disease Min, J., Cao, Z., Chen, H., Wang, X. and Xu, C., 2024. Trajectories of depressive symptoms and risk of cardiovascular disease, cancer and mortality: a prospective cohort study. General Psychiatry.
• Depression is associated with an increase in inflammatory markers such as acute phase proteins, chemokines, adhesions molecules and anti-inflammatory mediators such as prostaglandins Hassamal, S., 2023. Chronic stress, neuroinflammation, and depression: an overview of pathophysiological mechanisms and emerging anti-inflammatories. Frontiers in Psychiatry.
• Depression activates cell-mediated immunity (the part of the immune system not associated with antibodies and which is known as the body’s adaptive immunity) Frontiers in Psychiatry, 2026. The emerging role of T cells in depression. Frontiers in Psychiatry.
  • Activation of cell-mediated immunity refers to activation of the T-cells of the immune system Frontiers in Psychiatry, 2026. The emerging role of T cells in depression. Frontiers in Psychiatry. Foley, É.M., Parkinson, J.T., Mitchell, R.E., Turner, L. and Khandaker, G.M., 2023. Peripheral blood cellular immunophenotype in depression: a systematic review and meta-analysis. Molecular Psychiatry.
• Depression is associated with activation of the compensatory anti-inflammatory reflex system (CIRS)
  • CIRS is a system that controls acute inflammation and limits an overzealous acute inflammatory response
  • This is achieved by a number of methods, and includes dampening cytokine activity and therefore reducing inflammation

Research has provided evidence for depression-inflammation relationships developing early in life. There appears to be a circular relationship between depression and inflammation in children.

• Children with higher inflammatory cytokine levels were more likely to be depressed at age 18 compared with those with lower cytokine levels Khandaker, G.M., Pearson, R.M., Zammit, S., Lewis, G. and Jones, P.B., 2014. Association of serum interleukin 6 and C-reactive protein in childhood with depression and psychosis in young adult life: a population-based longitudinal study. JAMA Psychiatry.
• In a different study, involving children aged 9, 11 or 13 years, depression predicted the subsequent level of C -reactive protein (CRP)
  • C -reactive protein is a marker of inflammation and is raised in infection or inflammation in the bodyCopeland, W.E., Shanahan, L., Worthman, C., Angold, A. and Costello, E.J., 2012. Cumulative depression episodes predict later C-reactive protein levels: a prospective analysis. Biological Psychiatry.
• Evidence shows inflammatory markers were higher in about a third of depressed patients compared to the majority of non-depressed subjects Osimo, E.F., Baxter, L.J., Lewis, G., Jones, P.B. and Khandaker, G.M., 2019. Prevalence of low-grade inflammation in depression: a systematic review and meta-analysis of CRP levels. Psychological Medicine.

• An experiment which involved injecting Lipopolysaccharides (LPS) into animal bodies led to severe learning deficits
• These deficits were accompanied by an increase in beta-amyloid plaque in their hippocampus, and beta-amyloid plaque is a marker for Alzheimer’s disease

Behaviour and mood are heavily influenced by neurotransmitters and brain networks.

Cytokines, both pro-inflammatory and anti-inflammatory cytokines, are small proteins released by cells which have a specific effect on the interactions and communications with cells. Deckers, J., Anbergen, T., Hokke, A.M. et al., 2023. Engineering cytokine therapeutics. Nature Reviews Bioengineering.

Cytokines have been shown to interact with virtually every physiological process relevant to depression, including the processing and function of neurotransmitters.

• In research, administering cytokines profoundly affected the production, uptake and release of key neurotransmitters for mood and behaviour, serotonin, noradrenaline and dopamine Miller, A.H., Haroon, E., Raison, C.L. and Felger, J.C., 2013. Cytokine targets in the brain: impact on neurotransmitters and neurocircuits. Depression and Anxiety.

Increased cytokines levels were shown to lead to:

• Reduced serotonin levels (the neurotransmitter which regulates our moods, appetite and sleep)
  • Indeed cytokines are involved in the breakdown of serotonin
• Decreased dopamine uptake (the pleasure and reward neurotransmitter)
• Reduced GABA levels (the calming and focus neurotransmitter)
• Reduced levels of acetylcholine (the neurotransmitter involved in memory and stress) Liu, H., Zhang, X., Shi, P., Yuan, J., Jia, Q., Pi, C., Chen, T., Xiong, L., Chen, J., Tang, J., Yue, R., Liu, Z., Shen, H., Zuo, Y., Wei, Y. and Zhao, L., 2023. α7 nicotinic acetylcholine receptor: a key receptor in the cholinergic anti-inflammatory pathway exerting an antidepressant effect. Journal of Neuroinflammation.

There seems to be a symbiotic relationship between inflammation and stress hormones in that inflammatory cytokines can trigger the release of stress hormones; and conversely, elevated stress hormones can trigger inflammation.

Meanwhile, there is a correlation between high levels of stress hormones, inflammation and depression:

• The administration of inflammatory cytokines acutely impact the HPA axis, which is activated during the stress response Lei, A.A., Phang, V.W.X., Lee, Y.Z., Kow, A.S.F., Tham, C.L., Ho, Y.-C. and Lee, M.T., 2025. Chronic stress-associated depressive disorders: the impact of HPA axis dysregulation and neuroinflammation on the hippocampus – a mini review. International Journal of Molecular Sciences.
• Cytokines stimulate the release of hormones involved in the stress response such as corticotropin-releasing hormone (CRH),  adrenocorticotropic hormone (ACTH) and cortisol
• All these stress hormones are increased in patients with depression George, M.Y., Abdel Mageed, S.S., Mansour, D.E. and Fawzi, S.F., 2025. The cortisol axis and psychiatric disorders: an updated review. Pharmacological Reports.
• Conversely, impairment in the HPA axis activity due to chronic stress and the associated rise in cortisol can cause enhanced susceptibility to inflammation Kempter, E., Amoroso, M., Duffner, H.L., Werner, A.M., Langgartner, D., Kupfer, S. and Reber, S.O., 2021. Changes in functional glucocorticoid sensitivity of isolated splenocytes induced by chronic psychosocial stress – a time course study. Frontiers in Immunology.
• Chronic stress causes the activation of the HPA axis, and of inflammtory cytokines which can lead to suppressed immunity Tian, R., Hou, G., Li, D. and Yuan, T.-F. (2014). A possible change process of inflammatory cytokines in the prolonged chronic stress and its ultimate implications for health. [online] The Scientific World Journal. Available at: https://www.ncbi.nlm.nih.gov/pubmed/24995360 [accessed 11 Aug. 2026].

Autoimmune disease occurs when the body’s immune system attacks the body’s own cells and tissues. Therefore it involves an inflammatory response.

Types of autoimmune disease include:

• Rheumtaoid arthritis
• Systemic lupus erythematosus (SLE)
• Multiple sclerosis (MS)
• Psoriasis
• Crohn’s disease
• Hashimoto’s thyroiditis

The cause of autoimmune disease in many cases is unknown. There are many factors implicated:

• Autoimmune conditions are more common in females suggesting a hormonal component
• They can run in families, suggesting a genetic component
• There is a theory that they are caused by gut issues such as leaky gut or gluten intolerance

Christovich, A. and Luo, X.M., 2022. Gut microbiota, leaky gut, and autoimmune diseases. Frontiers in Immunology.

There is a correlation between autoimmune disease and mental health issues:

• Autoimmune disease and severe infections are risk factors for schizophrenia and other mental illnessAhmed, G.K., Ramadan, H.K.A., Elbeh, K. et al., 2024. The role of infections and inflammation in schizophrenia: review of the evidence. Middle East Current Psychiatry.
• A range of psychiatric disorders including psychosis has been observed to occur more frequently alongside autoimmune diseases
• In some studies, a prior autoimmune disease increased the risk of depression by 45% Benros, M. E., Waltoft, B. L., Nordentoft, M., Krogh, J. and Mortensen, P. B. (2012). Autoimmunity and infections as risk factors for depression and other severe mental illnesses. [online] Neurology, Psychiatry and Brain Research, 18 (2), pp. 40–1. Available at: http://www.sciencedirect.com/science/article/pii/S0941950012000152 [accessed 11 Aug. 2026].

Brain-reactive antibodies (antibodies which only affect brain tissue) and inflammation are the key factors implicated in the link between autoimmunity and mental health problems.

Brain-reactive antibodies are present in about 2-3% of the population and normally cause no harm.

Brain-reactive antibodies have been implicated in:

• Autism
• Obsessive-compulsive disorder
• Schizophrenia

These conditions are believed to originate during pregnancy in the developing foetus:

• Elevated levels of antibodies have been found at the end of pregnancy in mothers of children who later develop schizophrenia
• Elevated brain-reactive antibodies have been found in pregnant mothers and their children who later develop autism Bagnall-Moreau, C., Spielman, B. and Brimberg, L., 2023. Maternal brain reactive antibodies profile in autism spectrum disorder: an update. Translational Psychiatry.

In response to infection and/or inflammation, the release of inflammatory cytokines stops the development of new nerve cells in the brain known as “neurogenesis” or “neuroplasticity”.

Evidence indeed shows that infection and inflammation, which activate the release of cytokines, affect behaviour and cognitive functions such as memory.Nissen, T.A.D., Baig, A., Farmand, S., Rock, D.T., Shibu, S., Lee, H., O’Neill, L.A., Houghton, V., John, S., Klavinskis, L.S. and Thuret, S., 2026. TNF-α induces type I IFN signalling to suppress neurogenesis and recruit T cells. Nature Communications.

Just as inflammation and inflammatory cytokines can reduce neurogenesis, inflammation is also implicated in neurodegenerative diseases such as Alzheimer’s disease.

The chemical markers associated with inflammation are consistently raised in Alzheimer’s and can be used to predict cognitive decline and the development of dementia.Heneka, M.T., Bentsen, M.A. et al., 2025. Neuroinflammatory fluid biomarkers in patients with Alzheimer’s disease: a systematic literature review. Molecular Psychiatry.

During any physical illness, the immune system communicates with the brain through the secretion of cytokines.Filiano, A.J. et al. — actually the strongest match: Pinho-Ribeiro, F.A. and Deczkowska, A., 2025. Immune control of brain physiology. Nature Reviews Immunology.

Due to the interaction between the immune system and the brain, non-neurological infections such as pneumonia and urinary tract infection (UTI) can be accompanied by acute syndromes of brain dysfunction Kim, S. et al., 2026. Urinary tract infection-related delirium in Alzheimer’s disease and related dementias: clinical challenges and translational opportunities. Alzheimer’s & Dementia. characterised by delirium and confusion.Moorey, H.C., McCluskey-White, L.M., Andleeb, S., Botfield, H.F. and Jackson, T.A., 2025. A systematic review and meta-analysis of the role of peripheral inflammation in delirium. Brain and Behavior.

There is strong evidence associating infectious agents with mental health issues.

Infectious agents include:

• Bacteria
• Viruses
• Parasites
• Fungi
• Prions

These infectious agents can cause mental health issues, including cognitive, psychotic and mood disorders.

Viruses and bacteria

Viruses and bacteria can act as endocrine disruptors, disturbing hormonal balance. They can also create an inflammatory-immune response.

• Epstein barr Chen, W. et al., 2025. Epstein-Barr virus infection increases the risk of depression: a cross-sectional study and Mendelian randomization analysis. Journal of Affective Disorders.
• Cytomegalovirus

Prenatal infections in the mother are increasingly recognized as playing a role in the development of various brain disorders in the offspring such as:

• Depression
  • A prior history of hospitalization with infection increased the risk of depression by 62% Benros, M. E., Eaton, W. W., & Mortensen, P. B. (2014). The epidemiologic evidence linking autoimmune diseases and psychosis. Biological Psychiatry, 75 (4), pp. 300–6. Available at: https://www.ncbi.nlm.nih.gov/pubmed/24199668 [accessed 11 Aug. 2026].
• Schizophrenia
• Autism
• Bipolar disorder
• Mental retardation
• Cerebral palsy

HIV has been associated with a large number of psychiatric illnesses from depression to substance abuse.

Impaired cognition has been associated with several infections including:

• Herpes
  • Herpes simplex virus type 1 (HSV-1) causes cold sores, eye infection and encephalitis
  • Exposure to HSV-1 has been associated with cognitive impairment (memory tests) as well as emotion processing in otherwise healthy individuals
• Hepatitis
• HIV

Patients affected with sepsis (sepsis occurs when infectious agents (or toxins) enter the bloodstream and tissue and can cause serious organ damage and ultimately death if not treated) and encephalitis have been shown to have cognition issues long after the infection has cleared.

Schizophrenia is highly disabling, and so far the following infectious agents have been implicated as potential causes:

• Herpes type 2
• Borna virus
• Chlamydia infections
• Toxoplasmosis
  • Toxoplasmosis is a parasitic disease caused by ingesting food or drink contaminated with parasites shed from cats
  • Toxoplasmosis infection has been associated with a wide range of psychiatric disorders including schizophrenia, personality disorders and obsessive compulsive disorders

Fungal infections and mental health

Candida albicans is a fungal infection.

• Candida albicans is a new candidate for studies in connection with mental health
• Candida albicans has been associated with reduced cognitive function and potentially schizophrenia

Parasites and mental health

• All parasites emit toxins known as the indole catabolites. These burden the liver and kidneys and can make you become fatigued, irritable and can cause weight gain.
• Parasites are known to be connected to immune dysfunction, chronic fatigue, sleep disturbances, teeth grinding, IBS, anemia, joint aches and pains, skin conditions and constipation
• Parasites affect everyone differently. One person can be affected by parasites and not have mood problems and another person may get depressed or have digestive problems
• The parasite toxoplasma (which causes toxoplasmosis) is known to be correlated with generalised anxiety disorder twice as frequently as other parasites
• A study in 2006 showed that women with high levels of toxoplasma were more likely to give birth to children who later became schizophrenic and had birth defects Scott, T. and Gittleman, L. (May 2015). The Parasite/Anxiety Connection. [online] The Anxiety Summit, Season 3. Available at: http://season3.theanxietysummit.com/ [accessed 11 Aug. 2026]. 

• Sugars and refined carbohydrates Giannakopoulou, S., Antonopoulou, S., Chrysohoou, C. et al., 2024. The impact of dietary carbohydrates on inflammation-related cardiovascular disease risk: the ATTICA study (2002–2022). Nutrients.
• Processed and fried foods which are high in salt, sugar and bad fats (trans fats and hydrogenated fats)
• Nutritional deficiencies Roth-Walter, F. et al., 2024. Nutrition in chronic inflammatory conditions: bypassing the mucosal block for micronutrients. Allergy.
• Alcohol Lee, J., Lee, J.-Y. and Kang, H., 2025. Excessive alcohol consumption: a driver of metabolic dysfunction and inflammation. Frontiers in Toxicology.

• Often caused by food allergens such as gluten Ahmed, A., Dixit, K., Singh, A. et al., 2024. Sieving out non-celiac gluten sensitivity amongst patients with irritable bowel syndrome. Digestive and Liver Disease.
• Food allergies can be a major cause of brain inflammation Di Sabatino, A. et al. — actually the best matching, directly relevant, comprehensive source: Celiac disease and neurological manifestations: from gluten to neuroinflammation. International Journal of Molecular Sciences.

Fewer than seven hours a night.Kadier, K., Dilixiati, D., Ainiwaer, A., Liu, X., Lu, J., Liu, P., Ainiwan, M., Yesitayi, G., Ma, X. and Ma, Y., 2023. Analysis of the relationship between sleep-related disorder and systemic immune-inflammation index in the US population. BMC Psychiatry.

Lack of oxygen which could be due to:

• Poor breathing habits
• Insufficient exercise
• Urban living and pollution
• Superficial breathing due to chronic stress
• Poor circulation
• Iron deficiency

Sedentary behaviour may contribute to negative mood by enhancing the inflammatory signaling pathway and increasing mood disturbance.Werneck, A.O., Owen, N., Araujo, R.H.O., Silva, D.R. and Hallgren, M., 2023. Mentally-passive sedentary behavior and incident depression: mediation by inflammatory markers. Journal of Affective Disorders.

Excessive exercise or exercise which is too intense may lead to an excess release of stress hormones, physical damage, free radical damage and inflammation. This in turn may contribute to the development of mental health disorders.

• Gut dysbiosis and Leaky gut (which allows inflammatory substances such as Lipopolysaccharides (LPS) to pass through the gut barrier into the bloodstream, contributing to inflammation)
• Poor digestion Di Vincenzo, F., Del Gaudio, A., Petito, V., Lopetuso, L.R. and Scaldaferri, F., 2024. Gut microbiota, intestinal permeability, and systemic inflammation: a narrative review. Internal and Emergency Medicine.
• Use of medicines such as antibiotics, NSAIDs (non-steroidal anti inflammatory drugs), proton pump inhibitors Kiecka, A. and Szczepanik, M., 2023. Proton pump inhibitor-induced gut dysbiosis and immunomodulation: current knowledge and potential restoration by probiotics. Pharmacological Reports.

Toxins such as mercury and pesticides, are neurotoxins which can cause inflammation in the brain. Cresto, N., Forner-Piquer, I., Baig, A., Chatterjee, M., Perroy, J., Goracci, J. et al., 2023. Pesticides at brain borders: impact on the blood–brain barrier, neuroinflammation, and neurological risk trajectories. Chemosphere.

Toxicity and then inflammation can also be triggered by certain pharmaceutical and recreational drugs such as alcohol, antibiotics, contraceptive pills, etc.

Low grade, hidden or chronic infections Cifuentes, M., Verdejo, H.E., Castro, P.F., Corvalan, A.H., Ferreccio, C., Quest, A.F.G., Kogan, M.J. and Lavandero, S., 2025. Low-grade chronic inflammation: a shared mechanism for chronic diseases. Physiology.

Stress, whether acute or chronic, can cause an inflammatory reaction in the body and the brain. White, A.G., Elias, E., Orozco, A., Robinson, S.A. and Manners, M.T., 2024. Chronic stress-induced neuroinflammation: relevance of rodent models to human disease. International Journal of Molecular Sciences.

Trauma, whether physical or psychological, can lead to inflammation.

Chronic childhood trauma such as abuse will tend to cause mental health issues, not just for psychological reasons, but also for biochemical ones — the stress to the system involved in chronic trauma can lead to inflammation, which in turn can lead to mental health issues.