Our genes dictate that the body's cells stop dividing after they have divided between twenty and thirty times. New cells must be made to replace those that die, a process that slows with age. In addition, cells are subject to premature death and damage. When there are no longer enough new cells to replace the ones that have died or suffered damage, the result is aging. The free radical theory of aging has been the subject of a great deal of research in recent years, and has been gaining increasing acceptance.
Free radicals are atoms or groups of atoms that are extremely unstable and highly reactive.
If they are present in excessive amounts, they begin attacking the body on the cellular level. To make matters worse, the immune system may then attack the damaged cells as if they were foreign invaders. Because they are so chemically reactive, free radicals exist for only a millionth of a second each. This has made it difficult for researchers to study them directly. But there are millions of them, and even with their short life span they do considerable damage to our cells.