Inflammation is the body’s response to tissue damage or infection — a coordinated cascade of vascular, immune, and chemical events that clears damaged cells, fights pathogens, and initiates repair. It is not a disease. It is a defense mechanism. But when inflammation persists beyond its protective function or occurs inappropriately, it becomes a driver of disease — including chronic pain.
The acute inflammatory response
When tissue is damaged, the injured cells and resident immune cells release chemical signals — inflammatory mediators — that orchestrate the response:
Prostaglandins — produced from arachidonic acid by cyclooxygenase (COX) enzymes. Prostaglandins dilate blood vessels (increasing blood flow to the injured area), increase vascular permeability (allowing immune cells and proteins to leave the bloodstream and enter the tissue), sensitize nociceptors (lowering their firing threshold, producing tenderness), and contribute to fever. NSAIDs (ibuprofen, naproxen) reduce inflammation and pain by inhibiting COX enzymes, blocking prostaglandin production.
Histamine — released from mast cells. Produces vasodilation and increased vascular permeability. Responsible for the redness, swelling, and itching of allergic reactions. Antihistamines block histamine receptors.
Bradykinin — a peptide produced at sites of injury. Directly activates nociceptors, producing pain. Also increases vascular permeability and triggers prostaglandin release.
Cytokines — signaling proteins produced by immune cells. Pro-inflammatory cytokines (TNF-alpha, IL-1beta, IL-6) amplify the inflammatory response, recruit more immune cells, and can produce systemic effects (fever, fatigue, appetite loss). Anti-inflammatory cytokines (IL-10, TGF-beta) help resolve inflammation when the threat has been addressed.
The cardinal signs of acute inflammation — redness (increased blood flow), heat (increased blood flow and metabolic activity), swelling (fluid accumulation from increased vascular permeability), pain (nociceptor sensitization by prostaglandins, bradykinin, and cytokines), and loss of function (protective guarding) — are all direct consequences of these mediator cascades.
Inflammation and pain
Inflammation produces pain through two mechanisms:
- Direct nociceptor activation — bradykinin and certain cytokines directly stimulate nociceptors, producing immediate pain.
- Peripheral sensitization — prostaglandins, cytokines, and nerve growth factor lower nociceptor thresholds, making them fire in response to stimuli that would not normally be painful. This is why inflamed tissue is tender — the nociceptors have been chemically tuned to a lower threshold, producing hyperalgesia.
When inflammation resolves, these mediators are cleared, nociceptor thresholds return to normal, and pain subsides. This is the normal sequence in acute pain.
Chronic inflammation and neuroinflammation
When inflammation fails to resolve — because the triggering stimulus persists (chronic infection, autoimmune attack, ongoing tissue stress) or because the resolution mechanisms fail — it becomes chronic inflammation. Chronic inflammation drives tissue damage rather than repairing it: the same mediators that clear debris and fight pathogens, sustained over months or years, destroy healthy tissue.
Neuroinflammation is inflammation within the nervous system itself. Microglia (the brain and spinal cord’s immune cells) become activated and release pro-inflammatory cytokines that maintain neuronal hyperexcitability. This is a central mechanism of central sensitization — the nervous system’s own immune response sustaining the sensitized state that produces chronic pain. The inflammation is not in the originally injured tissue. It is in the neural circuitry that processes pain signals.
Inflammation and pharmacology
Inflammation is a major target of pharmacological intervention:
- NSAIDs — block COX enzymes, reducing prostaglandin production (anti-inflammatory, analgesic, antipyretic)
- Corticosteroids (prednisone, dexamethasone) — suppress multiple steps in the inflammatory cascade, reducing cytokine production and immune cell activity. Powerful but with significant side effects from prolonged use.
- Biologic agents (TNF-alpha inhibitors, IL-6 inhibitors) — targeted suppression of specific cytokines; used in autoimmune diseases (rheumatoid arthritis, inflammatory bowel disease)
- Antihistamines — block histamine receptors; used for allergic inflammation
Inflammation and the broader vault
Inflammation is not only a biological process. It has a structural analogue in Roberto Esposito’s analysis of immunity: the body’s inflammatory response is a defense system that, when chronically activated, damages the system it protects. Autoimmune disease — where the immune system attacks the body’s own tissue — is the biological equivalent of Esposito’s autoimmune community: a defense mechanism that has turned on its own constituency. The parallel is not metaphorical; Esposito argues that biological and political immunity express the same structural logic.
Related terms
- Tissue — what inflammation defends and, when chronic, damages
- Cell — the units that produce and respond to inflammatory mediators
- Homeostasis — the stable state that inflammation disrupts and, ideally, restores