Our normal cells can only divide about 50 times (Hayflick limit). Every time a cell divides, the 'Telomere' slightly shortens. Once that cap is completely gone, the cell ages and dies (Apoptosis). However, in HeLa cells, an enzyme called 'Telomerase' is over-active. This enzyme continuously patches up the DNA cap, preventing it from shortening. That is why the cancer cells never age, and never die!"