The epidermis is, collectively, composed of 4-5 layers of cells that form the outermost layer of skin. The bottom stratum, also referred to as the basal/germinal layer or stratum basale, contains the undifferentiated stem cells that go on to form the layers located above it, including the stratum spinosum, stratum granulosum, stratum lucidum and stratum corneum. Although the stratum basale contains the most stem cells, other cells in the layer include non-proliferating keratinocytes, melanocytes and dendritic cells.
