  Age spots are the brown spots that develop in the skin but change in color
and shape with time. To understand the mechanism of development of age spots,
characteristics of age spots are analyzed by Misrepair mechanism, a mechanism
introduced in Misrepair-accumulation aging theory. An age spot is
pathologically a group of aggregated basal cells, which contain lipofuscin
bodies. Accumulation of lipofuscin bodies is a sign of aging of a cell.
Characteristics of age spots include: inhomogeneity in distribution, growing
flatly before becoming protruding, irregularity on shape, inhomogeneity on the
color and on the protruding degree of a spot, and softness of a protruding
spot. After analyzing these characteristics, we make a hypothesis on the
process of development of an age spot. A. Aging of a tissue is the basis for
development of age spots. B. A flat spot results from accumulation of
lipofuscin containing cells. When an aged cell remains, this cell can
accelerate the aging of its neighbor cells by increasing damage sensitivity and
reducing repair efficiency of the local tissue. By a viscous circle, more and
more neighbor cells become aged and they form a flat spot, which has an
irregular shape. C. A protruding spot develops when some of the cells in a flat
spot die and release lipofuscin bodies. For the survival of an organism, the un
degradable lipofuscin bodies have to be isolated by a capsule made by fibrotic
membrane, for maintaining the structural integrity of local epidermis.
Successive deaths of lipofuscin containing cells make the capsule include more
and more dead substances by layers of fibrotic membrane. In this way, the spot
"grows" in three-dimension, resulting in protruding of the spot. In conclusion,
development of an age spot is a result of accumulation of aged cells in aged
skin.
