The skin has a very intricate microanatomical structure. In addition to thousands of skin cells, within one square inch of skin, varying from 0.04 inches (1 mm) to 0.16 inches (4 mm) in thick- ness, there are some 650 sweat glands, 65 hair follicles, 19 yards of capillaries, 78 yards of nerves, thousands of nerve endings, Merkel cells for sensory perception, and Langerhans cells for immunological protection. The skin also contains melanocyte cells responsible for producing the melanin that gives the skin its color and pigmentation spots, or freckles. For a solid visual understanding, draw a one-inch square and attempt to make 650 dots representing the sweat pores in the square. Then take a spool of thread, measure 19 yards, and place it within the square. If you are having a hard time with 650 dots and 19 yards of thread, imagine trying to add 1,300 nerve endings and 78 yards of nerves! All of this is found in one square inch of skin, about as thick as a few stacked sheets of paper.
The skin is home to a variety of glands. These glands are important not only because of their intrinsic functions but also because they represent a route of entry into the skin for certain chemical compounds. Their main function is to synthesize sub- stances that can cool the body, protect the skin, increase skin suppleness, or eliminate impurities such as mineral elements or cholesterol. Among these glands are the sebaceous glands and two sweat glands: the eccrine and apocrine glands.
Sebaceous glands, also known as oil glands, are attached to the same duct that contains the hair follicle. They are responsible for oil secretion in the skin, and are held within little sacs. The ducts of the oil glands open into the upper portion of the hair follicle. Usually, there is only one oil gland per follicle, but in some locations there may be more, resulting in greater oil (sebum) secretion in that area. Oil glands are found in almost all parts of the body. The face and back contain the highest number per square inch of skin, whereas the palms of the hands and soles of the feet contain none. The sebum secreted by the oil glands lubricates the skin and helps prevent the evaporation of moisture. It also possesses antifungal properties. Excessive oil secretion is associated with the development of acne, while insufficient oil secretion is associated with skin dryness.
It is important to note that dirt, impurities, and the asphyxiation, or clogs, seen in the pores occur in the hair follicle. They are the result of a mixture produced by oil and the keratinized and corneocyte cells present in the follicle. Cleansing the skin means eliminating impurities from these pores. Perspiration is not a cleanser. It may help clean the tiny opening of the sweat pores, but perspiration will not cleanse the hair follicle pore—the pore through which oil is secreted. This is a regular misconception by those who feel that saunas or perspiration cleanse the skin.
The surface of the skin is acidic. Its pH, also known as its protective mantle, is formed by a number of components. On the stratum corneum, these include naturally secreted sebum and perspiration (which contains lactic acid), as well as chemical reactions that occur in the epidermis, generating several relatively strong water-soluble acids. At the stratum corneum, the skin’s pH level ranges from 4.4 to 5.6, depending on the individual and the place on the body from which the reading is taken. It also appears to vary by individual and race. As one moves past the stratum corneum through the epidermis and into the dermis, the pH level increases and becomes neutral (pH 7.0) at the dermis. This process is not completely understood.
The skin’s acidity helps maintain the strength and cohesiveness of the skin, helps ward off infection by preventing the growth of bacteria, and allows for easier and more normal exfoliation of surface dead cells. One of the principal reasons why soaps— especially harsh soaps or cleansers with high pH values—are detrimental to the skin is because the skin needs an acidic environment to function properly. Thus, after the use of certain skin care cleansers, the use of a balancing lotion is needed. When cleansers have a neutral or alkaline pH, the skin’s acidic level needs to be restored. Left alone, the skin will regain its acidic value in about 20 minutes or more depending on the level of acidic imbalance created.
Sensations, such as cold, heat, pressure, vibration, and stretch- ing (both of skin and tendons), result from a stream of nerve impulses detected and transmitted to the brain by encapsulated nerve endings.
All of these components and actions are found within the basic building block of skin tissue, treated and discussed as three layers.