Telomeres are repeated sequences of DNA that are located at the end of eukaryotic chromosomes. Telomerase is an enzyme that maintains the length of telomeres. Many factors affect the length of telomeres, such as genetics, oxidative stress, and telomerase activity. When telomeres reach a critical length, chromosomal abnormalities may result and lead to apoptosis. Previous research has led to the telomere hypothesis of cellular aging, which states the loss of telomere limits the replicative capacity of cells and that with increasing age the number of cells going into replicative senescence increases. Dermal and epidermal tissues were found to be similar in their overall telomere length although there is a greater yearly loss in the dermis. Longer telomeres were found in the skin samples that were exposed to the sun, suggesting that UV light may promote telomerase activity. Consequently, telomerase expression does not change significantly with age, but greatly increases with sun exposure and is further expressed in photo-aged skin.