Skin & Hair - Your skin is your largest organ. If the skin of a typical 150-pound (68-kilogram) adult male were stretched out flat, it would cover about 2 square yards (1.7 square meters) and weigh about 9 pounds (4 kilograms). Skin protects the network of muscles, bones, nerves, blood vessels, and everything else inside our bodies. Eyelids have the thinnest skin, the soles of our feet the thickest. Hair is actually a modified type of skin. Hair grows everywhere on the human body except the palms of the hands, soles of the feet, and lips. Hair grows more quickly in summer than winter, and more slowly at night than during the day. Skin is essential to a person's survival. It forms a barrier that prevents harmful substances and microorganisms from entering the body. It protects body tissues against injury. Our skin also controls the loss of life-sustaining fluids like blood and water, helps us regulate body temperature through perspiration, and protects us from the sun's damaging ultraviolet rays.