Keratinocytes are the primary cell type of the epidermis and are developed in the basal layer. The epidermis is made of 95% keratinocyte cells. The stratum basale is the layer of the epidermis which covers the keratinocyte stem cells and differentiating keratinocytes. Cell proliferation and division occur in this layer. The main purpose of keratinocytes are to make a barrier to protect against microbial, parasitic, viral, and fungal invasion.