Telomeres are found in all living organisms and are created via an enzyme called telomerase. While telomerase is amply expressed in stem cells and germ cells, it is typically not expressed in somatic cells, or only at very low levels in some.

As telomeres shorten with each successive cycle of cell replication, cellular senescence is signalled once a critical telomere length is reached. Normal, healthy cells typically undergo a finite number of replicative cycles before the cell enters senescence and subsequently becomes destined for apoptosis (cell death). However, certain disease states have been found to correlate with shortening of telomeres and accelerated cellular aging, and further research is increasingly shedding light on the more active role telomeres play in various diseases. Telomere length can therefore be considered a dynamic biomarker of cellular aging.