Inflammation is the response of tissue to injury. It serves to fight the cause of injury as well as repair the consequences of injury. Classically it has five components: rubor, tumor, calor, dolor and functio laesa (redness, swelling, heat, pain and loss of function.)

Inflammation may be acute or chronic. Chronic inflammation may last for weeks or months and occurs in rheumatoid athritis, atherosclerosis, and persistant infections such as hepatitis and tuberculosis. During persistant inflammation the production of toxic substances by macrophages and other cell types may cause serious damage to tissues.