Stem cells are unspecialized cells that have two defining properties: the ability to differentiate into other cells and the ability to self-regenerate.
Stem cells have the wonderful power to develop into many different cell types in the body. When a stem cell divides, it can remain a stem cell or become another type of cell with a more specialized function like a skin cell. There are two types of stem cells, embryonic and adult.
Embryonic stem cells are exogenous in that they are harvested from outside sources, namely, fertilized human eggs. Once harvested, these stem cells are grown in cell cultures and manipulated to generate specific cell types so they can be used to treat injury or disease.
In contrast to embryonic stem cells, adult or somatic stem cells are endogenous. They are present in our bodies, from babies to adults, and serve to maintain and renovate the tissues in which they are found. Adult stem cells are found in many organs and tissues, including the skin. In actual fact, human skin is the largest depository of adult stem cells in the body. Skin stem cells dwell in the basic layer of the epidermis where they remain dormant until they are activated by tissue injury or disease.