Fibrosis is the transformation of certain tissues into a tissue composed of fibers, closely related to connective tissue. It often occurs as a result of tissue damage or an inflammation of tissue which does not regenerate properly: the initially healthy tissues are replaced by fibrous tissue. When tissue is injured, the normal development is towards healing, meaning the replacement of dead cells by identical cells whose functions are preserved. In case of an imbalance in the system used in this reparation phenomenon, there is an excessive production of collagen which leads to fibrosis. This follows almost the same pattern as chronic inflammation. Fibrosis can affect many organs such as the pancreas, kidney, liver, or lung.