Years ago, it was believed that the cells in our bodies were immortal, and they could replicate forever. Today we know about cell senescence, though very few people understand what it is, let alone the way it affects their bodies. To laymanise things: cells do not replicate forever, and, with few exceptions, there is a limit to how many times a cell can divide. This concept is now known as the Hayflick Limit and was discovered by our very own Doctor Leonard Hayflick. Jack Russo asks Leonard Hayflick to explain how he found this Nobel worthy discovery and the alarming reason why you don’t want to have immortal cells in your body.