Inflammation

Inflammation is the body's coordinated response to tissue damage or pathogens, executed through a fixed sequence of vascular and cellular changes rather than through anything specific to the cause. The same four cardinal signs — redness, heat, swelling, pain — show up whether the trigger is a splinter, a sprained ankle, or a bacterial infection, because inflammation is the response mechanism, not the injury itself. A sterile injury inflames every bit as much as an infected one; conflating "inflamed" with "infected" is a common and consequential error.

Mechanistically, injured or infected tissue releases signaling molecules — histamine, prostaglandins, and a family of cytokines — that dilate local blood vessels (the redness and heat) and make vessel walls more permeable, letting plasma and immune cells leak into the tissue (the swelling). Those same mediators sensitize local nerve endings, lowering their firing threshold, which is why an inflamed area hurts more than the raw tissue damage alone would predict.

Acute inflammation is this response running its normal course — hours to days, resolving once the threat clears and repair takes over. Chronic inflammation is the same machinery persisting for weeks, months, or indefinitely, often at lower intensity, and is now understood as a contributor to a long list of unrelated-seeming conditions (atherosclerosis, several autoimmune diseases, some cancers) precisely because a process built for short bursts of vascular leak and immune recruitment causes cumulative damage when it never switches off. Anti-inflammatory drugs (NSAIDs, corticosteroids) work by interrupting this signaling cascade at different points, which is also why they blunt pain and fever together — both ride the same mediators.