It is true that individual cells have a finite life span, and when they die off they are replaced with new cells. There are between 50 and 75 trillion cells in the body. Each type of cell has its own life span, and when a human dies it may take hours or day before all the cells in the body die. Red blood cells live for about four months, while white blood cells live on average more than a year. Skin cells live about two or three weeks. Colon cells have it rough: They die off after about four days. Sperm cells have a life span of only about three … Continue reading Benjamin Radford