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Cell senescence in vitro refers to the multitude of physio-logical, structural, biochemical and molecular changes that occur progressively during serial subcultivation of normal diploid cells, culminating in the permanent ces-sation of cell division. The whole duration of serial pas-saging is considered as the process of cellular ageing, and the end-stage irreversible growth arrest is termed as replicative senescence. The limited proliferative capacity ofnormal, diploidanddifferentiatedcells is alsoknownas the Hayflick limit, and the overall phenomenon is called the Hayflick phenomenon. A progressive loss of global deoxyribonucleic acid (DNA) methylation and of telo-meres is considered to be the critical determinants of the Hayflick limit. However, in vivo, it is not the absolute number of senescent cells which is responsible for age