The human skin is the largest organ covering the entire body and is made up of three layers, the epidermis, dermis, and subcutaneous layer . The epidermis is distinguished by five layers—the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and the stratum basale (stratum germinativum), from its exterior to the interior. The basal cells in the stratum basale divide continuously, and move toward the stratum corneum . Besides the keratinocytes, the epidermis contains other cells, such as Merkel cells, Langerhans cells, and melanocytes. The dermis is made up of connective tissue and it contains some extracellular matrix components, such as glycosaminoglycan and hyaluronic acid. The dermis possesses sweat glands, sebaceous glands , hair roots, nerves, lymph, and blood vessels. It contains three major cells—the fibroblasts, mast cells, and macrophages. There is a subcutaneous layer under the dermis containing several adipose cells that store fat and maintain body temperature . The skin has certain physiological functions, including protection from pathogens and the external environment, perception of pain or sentience, synthesis of vitamin D, temperature adjustment, absorption, and water resistance .