When I diagnose someone with inflammation I look for four cardinal signs. In Latin, these signs were defined by the Roman medical writer Aulus Cornelius Celsus and include redness (rubor), heat (calor), swelling (tumor), and pain (dolor). Redness is the result of small blood vessel dilation. Heat occurs when there is increased blood flow to an area. Swelling (edema) results when fluid accumulates outside of blood vessels which causes pain. All four of these indicators must be present in order for a diagnosis to be made.