As Hayflick limit is referred to in eukaryotes, the limited number of cell divisions, which a cell can undergo before the programmed cell death is initiated because the telomeres reach a critical length.
It was named after Leonard Hayflick, who discovered this limit in 1961. With his evidence that normal human cells ( unlike, for example embryonic cells ) divide about 52 times before finally using cell aging, he refuted the prevailing opinion by Alexis Carrel that cells are basically immortal. Hayflick observed telomere shortening through each mitosis, which further cell division is a natural end. The amount of natural pitches, and thus the Hayflick limit varies from species to species, and is an important factor that influences the life expectancy.
In each cell structure of the human body, there are so-called stem cells, many of which are not limited by the Hayflick limit. They form the enzyme telomerase or use other mechanisms to maintain telomere length. Telomerase is active in tumor cells and is one of the preconditions that they can divide uncontrollably.