Apoptosis is the natural process of programmed cell death (PCD) that occurs in multi-celled organisms. Billions of cells in a healthy adult die each day, either through simple changes or death. These cells are disposed from the body by being engulfed by other cells in order to control damage.

Apoptosis can be beneficial, such as in the creation of individual fingers and toes in a human embryo, or harmful, as with neurodegenerative conditions or tumor formations where apoptosis is excessive.