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Skin Sense!A Dermatologist's Guide to Skin and Facial Care
By Stephen M. Schleicher
iUniverse, Inc.Copyright © 2009 Stephen M. Schleicher, MD
All right reserved.
Chapter OneNORMAL SKIN
Our skin, the cutaneous organ, is composed of three distinct layers: the epidermis, the dermis, and subcutaneous (or fat) tissue. The following brief descriptions of each layer will greatly aid you in understanding both healthy and diseased skin.
The epidermis constitutes the outermost layer and is the only part of the skin that is visible to us. From a cosmetic standpoint, the epidermis is naturally of paramount importance.
The epidermis is the thinnest of all layers and over much of our body it is only one-sixteenth of an inch thick, about as thick as this page. The epidermis is thickest on the palms and soles, where it may reach nearly one-eighth of an inch.
The epidermis is composed of both living and dead cells. New cells are produced in the lowest portion, the basal layer. These cells migrate upward to the surface to become the cornified layer. Here the cells form a resilient, waterproof material known as keratin. Dead surface cells are continuously shed as miniscule flakes (scales) and are immediately replaced by living cells from the layers below. Some twenty-eight days are required for a new cell produced in the basal layerto finally reach the outer cornified zone; in other words, complete replacement of the epidermis takes nearly one month.
The epidermis is devoid of blood vessels. This alone gives some indication of the thinness of this layer, for we all have experienced bleeding following a superficial nick or cut. Thus even the most trivial of wounds easily traverse the thin epidermis to enter the next layer, the dermis.
The dermis is some forty times thicker than the epidermis. Besides harboring blood vessels, it also contains nerves, sweat glands, and sebaceous oil glands. The dermis feeds the cells of the basal layer and consequently regulates the growth of the entire epidermis. Tautness of the skin is in large part due to components such as collagen and elastin fibers that reside in the dermis.
The dermis rests on a thick pad of fat called the subcutaneous layer. This layer, like the epidermis, varies in thickness depending on body location. It is practically nonexistent within the eyelid and, as you might guess, becomes thickest around the waist (too thick in some cases!). The subcutaneous tissue serves as a thermal insulator and shock absorber.
Unhealthy skin may result from a disease process that affects any or all of the three layers. For example, dry skin involves changes in the epidermis; acne is a disorder of sebaceous glands located in the dermis; and cellulite arises from alterations in the subcutaneous tissue. You'll find more on these conditions in upcoming chapters.
Male and Female Skin
So, is male skin from Mars and female skin from Venus? Hopefully, we are all Earthlings, but differences in the sexes certainly carry over to our skin as well. Male skin is indeed thicker than female skin. Increased collagen and elastin fibers in men contribute to firmness and are a main reason why men tend to age with fewer deep-set wrinkles and fine lines than women. Another reason for aging disparity is the fact that male skin has a greater number of coarse hair follicles. Over time, exposure to solar radiation breaks down dermal collagen and contributes mightily to wrinkle formation, but facial hair (the male beard) acts as a physical screen to ultraviolet light.
Male skin has more active oil and sweat-gland activity than female skin; thus men have less need to moisturize. Bacteria living on the skin surface degrade sweat, leading to the characteristic musty aroma of the male armpit and the enhanced need for deodorants (at least when out in public!).
The placement of fat is to some degree sex-related and varies in males and females. The distribution in women gives rise to the more rounded contours associated with the feminine figure and in large part contributes to culturally defined "sexiness."
Black and White Skin
Pigment cells within the skin are called melanocytes, and the actual pigment is known as melanin. Melanin production varies among the various cultural groups, including Africans, Asians, and Caucasians. Interestingly, black skin does not contain more melanocytes, but it does tend to contain more melanin. The melanin granules are larger and darker.
Variations in human skin color have evolved over the ages. Black skin is the most resistant to ultraviolet light and is ideally suited to withstand chronic sun exposure. Indeed, unprotected white or pale skin is a sitting duck for skin cancer.
A redeeming feature of sunlight is that it induces production of vitamin D, which is extremely important for our health and well-being. Thus melanin serves as a double-edged sword. By blocking solar radiation, melanin protects against skin cancer, but it also prohibits vitamin D production. One can postulate that as humans migrated from sunnier climates to colder ones, skin lightening was a positive adaptation to a changing environment. The need for melanin to prevent skin cancer lessened with decreased sun exposure, and decreased amounts of melanin actually enhanced vitamin D production by skin cells.
NUTRITION AND THE SKIN
Three main food types are essential in the everyday maintenance of our body. These are carbohydrates, proteins, and fats, all of which contribute to healthy skin.
Despite occasional pitches to the contrary, a "superskin" diet has yet to be developed. Perhaps one day what we eat will indeed serve as a fountain of youth that thwarts the aging process. For now one would do best to follow the sound nutritional principles that medical doctors advocate for the majority of the population: a diet low in calories, high in fiber, and low in saturated fats.
The role of diet in causing or perpetuating our most common skin conditions is somewhat controversial. A diet rich in fat does not make the skin oilier, and drinking large amounts of fluid will not put moisture back into the skin. Does chocolate worsen breakouts? Possibly. Recent data suggests that eating refined carbohydrates and sugar leads to a surge in an insulin-like growth factor that triggers an excess of male hormones. Male hormones signal skin cells to excrete large amounts of sebum (oil). Increased sebum production is a contributing factor to pimple formation. An even stronger association has been made with milk; cow hormones present in milk have been linked to the development of acne.
On occasion one may become allergic to a particular food or food additive, resulting in hives. Common offenders include strawberries and shellfish. And one uncommon skin disease, called dermatitis herpetiformis, is actually linked to sensitivity to gluten, which is found in many foods, including bread and beer.
Marked fluctuations in weight may also affect the skin. Gaining pounds augments the amount of body fat, which in turn predisposes a person to stretch marks and cellulite. Rapid weight loss (from crash dieting, for example) may result in decreased skin turgor and may actually aggravate the cosmetic disfigurement that accompanies cellulite.
Vitamins and minerals are substances found in our food (and medicine cabinets) that are required in minute quantities for proper maintenance of the body. Botanicals are compounds that contain extracts or active ingredients derived from plants. Nutraceuticals are products that have been isolated or purified from food and are used for medicinal purposes. In regard to skin care, vitamins, minerals, botanicals, and nutraceuticals are utilized either internally (taken by mouth) or topically (placed on the skin). There is still much to be learned about the action and effects of these substances, and this most certainly contributes to the multitude of inflated claims associated with their use.
From the standpoint of our skin, one should note that substances such as minerals and vitamins, so essential to the human body in trace amounts, may or may not have beneficial effects when chemically modified or used in higher concentrations. One should note as well that the labeling of an herbal or botanical product as "natural" or "organic" means nothing in regard to efficacy. And the fact that something comes from a plant does not make it safe or effective-take tobacco and poison ivy, for example.
Vitamin A is a fat-soluble vitamin that plays a very important role in maintaining healthy skin. The substance is found in certain food items such as eggs, whole milk, and liver, and it is added to fat-free milk and many cereals. Retinol is an active form of the vitamin, and beta-carotene (found in green leafy vegetables) is a vitamin A precursor.
In the United States, vitamin A deficiency is a rare occurrence. An excess of this vitamin is usually the result of dietary supplement overindulgence. Because vitamin A is fat-soluble, it can be stored in the body and can accumulate in harmful levels. Too much vitamin A can damage the liver and may contribute to osteoporosis. Signs of acute toxicity included nausea, vomiting, headache, and visual disturbances. Pregnant women should avoid vitamin A supplementation since the substance is a known teratogen (inducer of birth defects).
Topical and oral vitamin A-based compounds are used to treat acne and psoriasis. Two FDA-approved derivatives, Renova and Avage, may diminish fine lines and wrinkles. The vitamin A compounds retinol and retinyl palmitate are found in over-the-counter products, and these too may improve the appearance of aging skin. Clinical trials comparing the efficacy of the prescription and nonprescription topical formulations of this vitamin are still lacking.
Biotin is a water-soluble B vitamin necessary for metabolism and growth. The compound is found in many foods including liver, soy products, carrots, and cereals. Deficiency is rare and curiously may be induced by a diet rich in raw eggs, as a substance in egg whites prevents intestinal absorption of the vitamin. The first signs of biotin deficiency involve the hair and nails, which lose luster and become brittle. Thus, intuitively, some believe that excess biotin (in pill form) will in fact strengthen these integuments. Biotin given to horses appears to enhance hoof quality, and anecdotal evidence in humans suggests that it may be of benefit to our hair and nails.
Vitamin C (ascorbic acid) is a water-soluble vitamin that plays a key role in the formation of collagen, a substance necessary for healthy bones, cartilage, muscle, and blood vessels. This vitamin is acquired mostly by eating fruits and vegetables, and healthy individuals who eat balanced diets rarely need supplementation. Vitamin C deficiency (extraordinarily rare in the United States) leads to a condition called scurvy, which is characterized by joint pains, muscle weakness, gum bleeding, and skin lesions. Except for gastric irritation, oral intake of large amounts of the vitamin does not appear to have serious consequences, nor does it appear to have much benefit despite at one time being touted as a cure for the common cold and a preventative of cancer.
Of late, vitamin C has been incorporated into a variety of over-the-counter preparations touting anti-aging and anti-inflammatory properties. Vitamin C is a powerful antioxidant that may, when used topically, stimulate collagen production and offer some level of protection against the damaging effects of sunlight. The problem is that vitamin C in topical formulations is highly unstable and rapidly breaks down when exposed to the environment (which is why most products are packaged in dark containers). More documentation of the stability, skin-penetrating abilities, and efficacy of currently marketed products is needed before they can be recommended from a therapeutic standpoint; but many vitamin C products are well tolerated and are formulated within elegant, moisturizing bases.
Vitamin D is a very hot topic, as recent data suggests that a significant percentage of Americans are deficient in this vitamin, and low levels have been linked to heart disease, cancer, and osteoporosis. Federal guidelines currently recommend that most persons get 200 to 600 IU daily, although these unit numbers will in all likelihood be increased, perhaps exceeding 1,000 IU for individuals age fifty and above. Vitamin D is found in fortified milk, fatty fish such as salmon, and in dietary supplements. It is also produced in the skin upon exposure to sun and ultraviolet light; hence it is called the "sunshine vitamin." Lighter skin produces more vitamin D than darker skin. Current thinking holds that as little as five minutes outdoors three times weekly allows many individuals to produce the necessary amount of this vitamin. However, dietary supplementation is highly recommended for those who cannot tolerate the sun, lack access to sunlight, are elderly, or have darker complexions.
Vitamin E is a fat-soluble vitamin found naturally in vegetable oils, nuts, and green leafy vegetables. Deficiency of this vitamin is quite rare, and the merits of supplementation are contested. Studies to date are inconclusive as to whether oral intake of high doses can ward off heart disease, cataracts, and even cancer. Indeed, vitamin E is a marvelous example of the hype associated with antioxidants and the aging process. Thirty years ago this vitamin was trumpeted as a retardant of cellular demise, helping to gobble up damaging free radicals, the harmful byproducts of metabolism and sun exposure. Megadoses were in vogue. But guess what? In 1994 the American Heart Association warned that high doses of vitamin E could actually increase the risk of death, and a study published in 2009 found no evidence that it prevented cancer.
Vitamin E has been used for decades as an ingredient in certain over-the-counter treatments for dry skin, and more recently, for its postulated anti-aging properties. Topical vitamin E (in the form of either alpha tocopherol or tocopherol acetate) has antioxidant properties, which in animal models protect epidermal cells from environmental damage such as that caused by sunlight. To date, human studies are inconclusive, perhaps in part because this vitamin, like vitamin C, has difficulty penetrating the skin.
Vitamin K is a fat-soluble vitamin which helps activate the clotting mechanism of our blood. This vitamin is found in cabbage, green leafy vegetables such as spinach, and soybeans. Deficiency of this vitamin may be induced by diseases that interfere with intestinal absorption, but is quite rare.
Several topical formulations contain vitamin K and claim to reduce the severity of bruising, diminish the appearance of tiny leg veins, and even improve dark circles under the eyes. Very little scientific data substantiates any of these claims, although one small study using topical vitamin K reported diminished bruising following laser treatment for facial blood vessels.
Zinc is an essential mineral that has diverse physiological functions and plays a critical role with enzymes and proteins needed to maintain healthy skin. It is found in abundance in beef, pork, lamb, and peanuts. Dietary deficiency of zinc is very unusual in the United States. Certain rare genetic disorders are characterized by the inability to absorb zinc, resulting in inflamed skin and rashes. Topical zinc has anti-inflammatory and antibacterial properties and is incorporated into shampoos (for example, DHS Zinc and Head & Shoulders) to control dandruff. Oral zinc supplementation has been reported to improve acne, although evidence of a beneficial effect is far from convincing.
Nicotinamide (or niacinamide) is a derivative of niacin, a component of the B vitamin complex. These compounds enable our cells to produce energy and also help repair damage to DNA induced by sun exposure. A deficiency of this vitamin is quite rare but leads to the condition known as pellagra, which is characterized by dementia and a skin rash. B vitamins are found in a variety of plant and animal food sources.
Excerpted from Skin Sense! by Stephen M. Schleicher Copyright © 2009 by Stephen M. Schleicher, MD. Excerpted by permission.
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