A glance at the cross-section will show you how complex the skin is. A typical patch of skin the size and thickness of a quarter contains about 30 million cells, 600 sweat glands, 100 oil glands, 20 blood vessels, 65 hair follicles, and thousands of nerve endings.
Living skin is made up of two distinct layers lying on a bed of fat globules separating it from the muscles and bones below. A microscopically thin layer of dead cells called the stratum corneum (horny layer) lies between the skin and the outside world.
The innermost and thickest layer of skin is called the dermis. This is where you will find collagen and elastin fibers, which give skin its strength and flexibility; tiny blood vessels called capillaries; a dense network of nerves; parts of the lymph system, which help fight disease and infection; and the hair, sweat, and oil glands.
The next layer, the epidermis, is one-quarter the thickness of the dermis. It contains rapidly reproducing skin cells. As new cells are made, the older ones migrate toward the skin surface, collecting increasing amounts of a protein called keratin as they go. Once they reach the stratum corneum, the cells are made mostly of keratin and are considered dead. Over the course of about a month, they flake off, making room for the next generation of cells.
There are no blood vessels in the epidermis, but it does contain nerves and melanin cells. Melanin is a dark brown pigment that is responsible for the color in freckles, moles, birthmarks, suntan, and skin color in general. The darker a person’s skin, the more melanin cells it contains. People with albinism, a hereditary disease, have no melanin at all. Their skin is very pale and their hair white.
The Hair Facts
Hair is really just a special kind of skin. The visible part is made mostly of keratin, and the color comes from melanin – lots of it produces black or dark brown, less of it is blond, and none at all is white. Except for your eyelids, lips, palms, soles, nipples, and parts of the external genitalia, your entire body is covered with hair. Some of it is clearly visible, some of it so fine that you may doubt it’s really there. A very specialized kind of hair grows at the tips of your fingers: your nails!
Strictly speaking, the part of hair that meets the outside world is dead, but the living roots lie deep in the skin. Hair grows out of follicles located in the dermis and emerges at the skin surface through tiny holes called pores.
Each follicle is surrounded by nerves and blood vessels. Close neighbors are always a sweat gland, which keeps the hair moist, and a sebaceous (oil) gland, which secretes a waxy substance to seal the moisture in. This arrangement, which keeps hair lustrous and shiny, can cause skin problems, especially during adolescence.
Attached to the side of the follicle is an erector muscle, which makes the hair stand up or lie down in response to such stimuli as fear and cold. In humans it’s called “goose bumps,” but the same thing happens when a porcupine or cat gets angry.
What’s It For?
Simply put, skin protects your insides from the outside. It regulates the body’s temperature and moisture levels; it acts as a shield against objects large and small; and it provides a vital barrier against harmful radiation from the sun. It is also the first line of defense against infection. And in case you never noticed, like the bright-colored feathers of birds, the appearance of human skin and hair plays an important role in attracting the opposite sex.
Did you know that lie detectors rely on sweat to get at the truth? A phenomenon known as the galvanic skin response occurs when a weak electrical current is passed through the skin. It is caused by changes in the sweat glands when a person is under stress. You probably know about that if you’ve ever taken a really hard exam or been nervous before a job interview or performance on stage. And you’ve probably wondered why on earth you need sweat glands in the first place.
Sweating is one of the body’s best ways of controlling internal heat. When you feel hot, your sweat glands secrete a watery fluid; the skin cools as the fluid evaporates. High temperatures in the environment, fever, and nervousness all can cause this response.
It may surprise you to learn that sweat is actually odorless. The familiar “sweaty” smell actually is caused by bacteria that mix with the sweat on the way to the surface. Although you have sweat glands all over your body, special ones (called apocrine glands) located in the underarm and groin areas are the ones that are prone to bacterial growth and resulting odor. The apocrine glands become active in adolescence, one of the many body changes that you are becoming aware of.
The best defense against body odor (B.O.) is bathing regularly. Using a soap and deodorant with antibacterial ingredients may help keep you smelling fresh.
The Oily Age
All in all, Mother Nature did a great job of designing skin. But there is one glitch. Sometime between the ages of 9 and 14, the human body starts churning out the hormones that tum a child into an adult. In boys the main hormone is called testosterone; in girls it’s estrogen. Growth spurts, muscle development, new curves and contours are features of this hormone activity. And so is stepped-up production in the sweat and oil glands of the skin. The result: Just when things are getting good, skin problems come along to spoil the fun.
Sometimes the problem is minor – a few clogged pores, the occasional zit, and hair that seems to need washing more often. At other times, full-blown acne clouds what ought to be the best years of your life.