The hayflick limit was discovered by Leonard Hayflick in 1965. Hayflick observed that cells dividing in the human lungs divided only a certain number of times, then they died. The number of times they divided was always the same (about 50), a seeming limit to the number of times the cells could divide. As the cells approached this limit, they began exibiting more and more signs of old age.

This limit to the number of times a cell divides has been noted in all human cell types, as well as in other organisms. It varies from cell type to cell type, and more significantly from organism type to organism type. The human limit is around 52. The limit has been linked to the shortening of telomeres, a region of DNA at the end of chromosomes.

The limit is believed to be one of the causes of aging. It is believed that if the shortening of telomeres can be slowed or prevented, life expectancy can be extended. Much research is happening in this area.

The limit is also believed to help prevent cancer. If a cell becomes cancerous and the hayflick limit is taking place, the cell will only be able to divide a certain number of times. Once it reaches this limit, the formed tumour will no longer be able to reproduce and the cells will die off. Cancers become problems have often found ways around the hayflick limit.