Your skin is your body’s largest organ and acts as a barrier to the outside world. It covers your entire body and has a surface area of around 21.5 square feet (2 square meters). Its thickness ranges from 0.02 inch (0.5 millimeter) on your eyelids to 0.16 inch (4 millimeters) or more in “tougher” areas, such as on the palms of your hands and the soles of your feet. In total, it accounts for around 16 percent of your body weight. Your skin protects your internal organs from infection and helps control body temperature.
Your skin consists of three main layers. The outer layer, called the epidermis, contains skin cells, pigment, and proteins. The middle layer, called the dermis, contains blood vessels, nerves, hair follicles, and oil glands, and it provides nutrients to the epidermis. The layer under the dermis, called the subcutaneous layer, contains sweat glands, some hair follicles, blood vessels, and fat. Each layer also contains connective tissue with collagen fibers to give support and elastin fibers to provide flexibility and strength. Cells in the deepest layer of your epidermis are constantly dividing to make new cells, providing your skin with a durable overcoat, which protects deeper cells from damage, infection, and dryness. Cells on the surface of your epidermis flake off and are continuously replaced with new ones, so that about every 30 days your body produces a whole new set of skin. A human body sheds about 600,000 particles of skin every hour—that’s about 1.5 pounds (0.68 kilogram) a year. By age 70, an average human will have lost 105 pounds (47.6 kilograms) of skin.