Creation Rebirth

Over time, Tsunade concentrates her chakra to a spot on her forehead that takes the form of a diamond. When she releases the seal, the chakra disperses and stimulates the proteins of her body to increase the speed of cell division and reconstruction of cells for as long as she has enough chakra. This allows her to recreate all organs and tissues, thus it is known as the absolute pinnacle of medical ninjutsu. The technique itself does not regenerate the old cells, rather it hastens the creation of new ones through division.

However, a body's cells can only split a certain number of times in a lifetime, and by speeding up this process, Tsunade is shortening her natural lifespan but will make look like she is 80 and feel like it but after she rest she will become 50 again and the mark will reaper how ever Tsunade great healing ability's she might find a way to increase the cell reparation. To what degree is unknown, but what is clear is that it is not great enough to cause her to die in battle, as she herself says that she gains a form of "immortality" throughout the duration of the technique.

Trivia

 * According to the second databook, Creation Rebirth was developed by Tsunade for the sake of continuing to protect the lives of her comrades. That is the resolution hidden in this technique.