It occurs over seconds, minutes, hours, and days, of the tissue injury and end when the injurious stimulus has been removed. The initial response is essentially the same regardless the nature of the stimuli.
During acute local inflammation, the response remains specific to a particular region of the body (for example, tennis elbow or a mosquito bite). It is the initial response of the body to harmful stimuli resulting the basic symptoms (redness/rubor), heat / calor, swelling /tumor, and pain /dolor and deranged function /functio laesa) of inflammation in the affected area.
Redness is caused by the dilation of small blood vessels in the area of injury. Heat results from increased blood flow through the area (experienced only in peripheral parts of the body such as the skin).
Fever is brought about by chemical mediators of inflammation and contributes to the rise in temperature at the injury. Swelling, called edema is caused primarily by the accumulation of fluid outside the blood vessels.
Certain chemical mediators of inflammation, such as bradykinin, serotonin, and the prostaglandins, distortion of tissues due to edema and compression of nerves by swollen tissue, generate pain.
Loss of function may result from pain that inhibits mobility or from severe swelling that prevents movement in the area.
All these five symptoms of inflammation can be seen if the inflammation occurs on the body’s surface. If the inflammation occurs in internal organs all these five signals may not appear.
Since in most cases it remains localized to a specific area of the body it is relatively easy to treat with medicines and proper care.
Although acute inflammation is usually beneficial, it often causes unpleasant sensations, (usually temporary) such as the pain of a sore throat or the itching of an insect bite.
Occasionally, an acute inflammatory reaction is severe and becomes systemic eg. major trauma, a severe and overwhelming infection that spreads outside of a local area, a very strong allergic reaction etc.
In each of these cases, there is a major acute response that is mediated by the immune system.