What Is Skin?
Apart from protecting our body, skin is a vital element in our physical make-up and well-being. It helps to regularize our body temperature and enables us to sweat. Thanks to the thousands of different nerve endings in our skin we can sense touch, pain, cold, heat and many other kinds of sensations. In a minor way we can also get rid of certain waste substances through our skin.
In man the skin varies considerably in thickness according to the area of the body covered. For example, the skin of our eyelids is approximately one-twenty-fifth of an inch or 1 mm, whereas on our palms and on the soles of our feet it reaches a thickness of about an eighth of an inch or 3 mm.
Human skin has five layers—the basal cell layer, the stratum spinosum (which is several cells thick), the stratum granulosum, the stratum lucidum and, finally, the surface layer which is called the stratum corneum. This can consist of as many as 20 layers of cells but the cells nearest the surface tend to flake off.
Skin is practically waterproof and this quality allows the fluid “body” to live and function in dry air. There are many varieties of skin diseases and the skin also reflects in the form of rashes diseases that attack the body—chicken pox, measles and scarlet fever are examples.
One of the most obvious attributes of skin is its capacity to support hair growth but in man hair on the skin has little practical function or purpose. Hair is continually shed and replaced. The average life-span of the soft, downy hairs is only a few months while the long tougher hairs on the scalp can have a life of several years. Most of the human body’s skin is actually covered by hair although for the most part the hair is so fine that we cannot see it without a magnifying glass. However, human beings do not grow hair on the soles of their feet or on the palms of their hands.
In one sense we can be said to register emotions through our skins, since any emotional stimulation can produce perspiration of the skin on the hands, feet and under the armpits. One of the main functions of skin is to act as an early warning system to the rest of the body about outside conditions. Skin remains taut and supple during most of our lives, but in old age, when the muscles begin to slacken, it loses this elasticity.
In humans, skin pigmentation varies among populations, and skin type can range from dry to oily. Such skin variety provides a rich and diverse habitat for bacteria that number roughly 1000 species from 19 phyla, present on the human skin. Skin has mesodermal cells, pigmentation, such as melanin provided by melanocytes, which absorb some of the potentially dangerous ultraviolet radiation (UV) in sunlight.
It also contains DNA repair enzymes that help reverse UV damage, such that people lacking the genes for these enzymes suffer high rates of skin cancer. One form predominantly produced by UV light, malignant melanoma, is particularly invasive, causing it to spread quickly, and can often be deadly. Human skin pigmentation varies among populations in a striking manner. This has led to the classification of people(s) on the basis of skin color.
The skin is the largest organ in the human body. For the average adult human, the skin has a surface area of between 1.5-2.0 square meters (16.1-21.5 sq ft.). The thickness of the skin varies considerably over all parts of the body, and between men and women and the young and the old.
An example is the skin on the forearm which is on average 1.3 mm in the male and 1.26 mm in the female. The average square inch (6.5 cm²) of skin holds 650 sweat glands, 20 blood vessels, 60,000 melanocytes, and more than 1,000 nerve endings. The average human skin cell is about 30 micrometers in diameter, but there are variants. A skin cell usually ranges from 25-40 micrometers (squared), depending on a variety of factors.