Differently from the
melanotic nevi and the
verrucous nevi on the skin, age spots change in color and in shape with time. Wang-Michelitsch and Michelitsch propose a hypothesis inspired by their misrepair-accumulation aging theory for the development of age spots. They propose that aged
basal cells contain
lipofuscin bodies that cannot be removed and might promote the aging of neighboring cells, generating a feedback loop that causes more and more neighbor cells to become aged and contain lipofuscins. has reported that "age spots" taken from human skin biopsies of patients facial senile lentigo of Fitzpatrick skin type III or IV aged 55–62 are enriched with
senescent fibroblasts compared to surrounding skin. The dark coloration appeared to be due to higher
melanin levels and activity of
tyrosinase in the senescent fibroblasts than in the controls, potentially related to lower
SDF1 expression. Patients were then administered six weekly treatments of microneedle fractional radiofrequency aimed at eliminating
dermal senescent fibroblasts; this led to a marked decrease in epidermal pigmentation compared to baseline, accompanied by a decrease in the synthesis of collagen and the normalization of suppressed SDF1 expression. == Prevention ==