Cell damage (also known as cell injury) is a variety of changes of stress that a cell suffers due to external as well as internal environmental changes. Amongst other causes, this can be due to physical, chemical, infectious, biological, nutritional or immunological factors. Cell damage can be reversible or irreversible. Depending on the extent of injury, the cellular response may be adaptive and where possible, homeostasis is restored.[1] Cell death occurs when the severity of the injury exceeds the cell's ability to repair itself.[2] Cell death is relative to both the length of exposure to a harmful stimulus and the severity of the damage caused.[1] Cell death may occur by necrosis or apoptosis.