The skin is the largest organ of the human body and it protects a human being�s inner organs from the environment 1. The skin consists of three layers: from outer to inner they are the epidermis, dermis, and subcutaneous fat layer. Figure 4.1 shows the structure of the skin, in which the epidermal layer is colored red, the dermis is colored pink, and the subcutaneous fat layer is colored yellow 2. © 2014 by Taylor & Francis Group, LLC.