Apoptosis, or programmed cell death, is a process by which cells deliberately destroy themselves. The process follows a natural sequence of events controlled by the genes within a nucleus: First, the chromosomal DNA breaks into fragments, followed by the breakdown of the nucleus. The cell then shrinks and breaks up into pieces (called vesicles) that are absorbed (phagocytosis) by macrophages and neighboring cells.

While programmed cell death may seem counterproductive at first glance, it plays an important part in maintaining the life and health of all living organisms. During human embryonic development, apoptosis removes the unnecessary webbing between the fingers and toes of the fetus; it is also vital to the development and organization of both the immune and nervous systems.