Thick and Thin Skin: Getting a Grip on Their Differences
The skin is the largest organ in the body, weighing about 4 kg. Though it appears uniform in structure and function. Its thickness in fact varies, from less than 1 mm covering the eyelids to more than 5 mm on the upper back. Many of the functional differences between skin regions reflect the thickness of the epidermis and not the skin's overall thickness. Based on epidermal thickness, skin can be categoraized as thick (about 1 mm deep) or thin (about 0.1 mm deep).
Areas of the body exposed to significant wear and tear (the palms, fingertios, and bottoms of the feet and toes) are covered with thick skin. It is composed of a thick stratum corneum and an extra layer not found in thin skin, the stratum lucidum, both of which make thick skin resistant to abration. Thick skin is also characterized by epidermal ridges (e.g, fingerprints) and numerous sweat glands, but lacks hair and sebaceous (oil) glands. These adaptations make the thick skin covering the hand and feet effective for grasping or gripping. Thick skin's dermis also contains many sencory receptors, giving the hands and feet a superior sense of touch.
Thin skin covers area of the body not exposed to much wear adn tear. It has a very thin stratum lucidium. Though thin skin lacks epidermal ridges and has fewer sensory receptors than thick skin, it has several specializations that thick skin does not. Thin skin is covered with hair, which may help prevent hear loss from the body. In fact, hair is most densely distributed in skin that covers regions of great heat loss--the head, axille (armpits), and groin. Thin skin also contains numerous sebaceous glands, making it supple and free of cracks that may let infectious organisms enter.