The stress hormone cortisol causes pre-mature aging of the immune system. Cortisol shortens a protective cap called telomere that allows the cells to keep dividing. The shorter the telomere, the shorter the cell’s lifespan will be. Telomeres shorten every time a cell divides the telomere shortens, acting like a clock for each cell.
The reason cancer cells are so strong is because their telomeres don’t shorten enough during cell division. A healthy cell lives a proper and preset time. An unhealthy cell either lives too short, not allowing the body to replace it time, or too long, allowing uncontrolled growth.