It is referred to as the Hayflick Limit which is a premise that explains the concept behind how the cells in the body ages. It explains that such mechanism limits the human cells to divide (this is called mitosis) only forty to sixty times before deteriorating. After its mitosis limit, it reaches its senescence which means it will not divide ever again. Instead, cells will only commit suicide by means of apoptosis. Interestingly all organisms are affected by this molecular clock that only keeps on ticking from the moment of birth to eventual death.