Inflammation is the first reaction of the immune system to an infection or irritation. First the organ involved gets red, then it will get hot, then it will swell, and then it will hurt. Finally it will stop working. The first four of these reactions have been known for a long time, since Antiquity. Finding them is attributed to Celsus. The last one was added by Rudolf Virchow in 1858.
Inflammation can also be present/responsible for skin disorders such as psoriasis/dandruff, joint pains, arthritis etc.