Greg Macpherson, biotechnologist, pharmacist and author of “Harnessing the Nine Hallmarks of Aging,” returns to Late Night Health. He talks about senescent cells, also known as "zombie cells," which accumulate with age and are associated with many disease states people experience later in life, can add a roadblock to your health now. Senescent cells are defined as cells that, over time, stop dividing but do not die off (which is how they got the nickname “zombie cells”).