Fig. 1

Cross-section of the human skin. The human skin is composed of the epidermis, dermis and subcutaneous tissue. The epidermis is a multilayered keratinizing squamous epithelium with keratinocytes representing the most common cell type in this skin layer. The stratum basale and stratum spinosum also harbor Merkel cells, melanocytes, T cells, and Langerhans cells. These four cell populations account for about 10% of epidermal cells. The dermis is home to immune cells, such as granulocytes and lymphocytes, and connective tissue-forming cells (fibroblasts). While collagen fibers and elastic fibers form the cellular fundament, blood and lymph vessels are also interwoven throughout this layer. As a form of elongated invagination, the hair follicle reaches out into the dermis. Sebaceous glands are located in close proximity to the hair follicle and its stem cells