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The
Skin
Structure
of Skin: Epidermis, Dermis, and Subcutis
The
Epidermis
The
Dermis
The
Subcutis and Subcutaneous Adipose Tissue
Skin
Firmness, Elasticity, and Moisture-holding.
Major
Skin Molecules - Collagen, Elastin, GAG’s and Proteoglycans
Nutrient
Supplements of GAG Sugars
Collagen
and Elastin in Cosmetics Have No Effect on Skin
Sebaceous
Glands and Eccrine (Sweat) Glands
Skin
pH and the Acid Mantle
Human
Pheromones (Attractants) and Apocrine Glands
Aging
and Sun Damaged Skin
Development
of Common Skin Lesions
Age
Spots
Actinic
Keratosis
Seborrheic
Keratoses
Cherry
Angiomas
"Broken
Capillaries" or Telangiectosia
Shingles/Herpes
Zoster
Varicose
Veins
Skin
Damaging Eczema and Dermatitis
Atopic
Dermatitis or Atopic Eczema
Contact
Dermatitis
Dandruff,
Seborrhea and Seborrheic Dermatitis
Seborrheic
Dermatitis
The skin is our principle organ of beauty, touch, pleasure, and sensuality. Your skin is the largest organ of the body, accounting for 12% to 16% body weight covers 12 to 20 square feet. With age the amount of subcutaneous (under-the-skin) fat is reduced resulting in a looser look to the skin.
The approximate chemical composition of the skin is:
Water 70.0%
Protein 25.5%
Lipids 2.0%
Trace Minerals 0.5%
Other 2.0%
The skin's barrier has a difficult dual function. First it must protect the body against invasion from microorganisms and against losing fluid and drying out. However, this barrier must still be open and permeable enough to allow an exchange of warmth, air and fluids. It also must act as the sensory organ for our delicate sense of touch. The skin regulates the body temperature by evaporating water. The skin replaces itself about every 27 days and continuously produces a horny protective cover of hardened proteins (keratinization) while shedding the outermost layer of dead cells (exfoliation).
Structure of Skin: Epidermis, Dermis, and Subcutis
Technically skin is of three layers : the epidermis ("overskin”) or top
layer, the dermis ("skin”) or middle layer and the subcutis (“underskin”)
or bottom layer. The outer surface of the skin, the epidermis, is comprised
of hard, flattened dead cells. Beneath this are living cells which are
somewhat larger, and at deeper layers of the skin, the skin cells are larger
and more round. At the bottom layer, there are new cells growing and pushing
upward to the surface. As cells are pushed to the surface, they become
flattened and lose most of their water content through pressure and dehydration.
The epidermis is the thinnest skin layer at a maximum 1 millimeter or as thin as a pencil line. It is thickest on the soles of the feet and the palms of the hands and its thinnest on our eyelids. The epidermis also produces the hair, toenails and fingernails. The epidermis consists of three interwoven types of cells: the keratinocytes which make the protein keratin, the melanocytes which produces the suntanning pigment melanin (which protects us from ultraviolet radiation and determines your skin color), and the Langerhans cells which are part of the immune system and intercept foreign substances that try to pass through the skin.
The epidermis itself forms four distinct layers with an average thickness of 0.25 mm. - the top outer layer called corneal layer and made from dead, hard, tough cells that form the hard skin surface. The three lower layers are called the stratum germinativium which, from bottom to top, are the basal layer, which produces millions of new cells at the bottom of the epidermis every day. Squamous cells lie just below the hard outer surface of the skin. The new cells start as soft, columnar cells then undergo a differentiation process and are transformed into the hard, flat cells of the outermost layers as they are pushed to the surface.
The most important types of protective substances in the outer layer of skin are the keratin proteins and the skin lipids. The outer layer becomes a formation of 15-20 layers of horny cells (like the horns of cattle) that are embedded in a matrix of skin lipids. Every several days these horny cells is sloughed off layer by layer and replaced by new cells from below.
The epidermis has numerous nerve endings that make the skin a sensory organ which detects warmth, cold, light, taste and touch. Your skin shows emotions such as when fear causes the skin to grow pale and embarrassment causes a red blush.
The dermis is a thick, supple and sturdy layer of connective tissue and makes up about 90 percent of the skin's thickness. The dermis a dense meshwork of collagen and elastin fibers, two connecting proteins. This meshwork supports tiny lymph and blood vessels that allow the skin to breathe and be nourished as well as the nerves, muscle cells, sweat and sebaceous glands, and hair follicles. This layer contains the special cells that repair the skin, such as the fibroblasts that synthesize the skin proteins like collagen and elastin.
The sebaceous glands make the special oils for the skin and hair. Normal functioning of the sweat and sebaceous glands is essential for healthy skin. Together these glands provide the "acid mantle", the natural covering which protects the skin. The sebaceous glands in this layer are found at the base of each hair follicle. They secrete an oily substance called sebum which waterproofs the hair and lubricates the skin. Overproducing sebaceous glands, which often occurs in adolescence, leads to the formation of blackheads and pimples.
The dermis also contains the sweat glands (which are vital to cool the body) plus apocrine
glands of the armpits, the ear canals, the nipples, and around the genitals
that secrete chemicals called pheromones. Pheromones act as smells that increase
interpersonal bonding and sexual attraction. At the lower (inner) portion
of the dermis the hair follicles are anchored. The dermis is the skin layer
that absorbs most of the substances that penetrate into the skin.
The subcutis is the deepest layer of the skin, composed primarily of fat. The subcutaneous layer manages the skin's functions of feeding, excreting and heat exchange. The key cells are fat cells or adipocytes that provide energy, serve as a heat insulator for the body, and act as a shock absorber to protect underlying tissue against mechanical trauma and helps give your skin its resilience. Among mammals, only humans and marine mammals such as whales and dolphins have this subcutaneous layer of fat. Sweat glands originate in this layer and excrete waste matter through perspiration. This sweat controls the body's temperature by evaporating and cooling the skin surface. "Goose-bumps" occur when the fine layer of muscles found in this layer contract.
Skin Firmness, Elasticity, and Moisture-holding.
Collagen and elastin are the skin proteins responsible for elasticity, tone and texture. Glycosoaminoglycans (GAG's or mucopolysaccharides) and proteoglycans hold water in the skin (these are very similar to mucus proteins) and are the true skin moisturizers. In contrast, cosmetic moisturizers cover the skin with a water impermeable barrier such as petrolatum or a heavy oil. This artificially slows the loss of moisture from the skin and gives the skin a temporary appearance of plumpness and fullness.
Major Skin Molecules - Collagen, Elastin, GAG’s and Proteoglycans
Collagen forms the structural network of our skin and is the most abundant protein in the body. It is primarily composed of glycine, proline and hydroxyproline. It is one of the strongest proteins in nature and gives skin its strength and durability. As we age, it is believed that collagen begins to deteriorate and causes the skin to become thinner and eventually sag. Elastin is similar to collagen but is a more stretchable protein that maintains the skin's elasticity. It provides the matrix that holds individual skin cells in place. Elastin also contains two unique amino acids, desmosine and isodesmonsine. The two proteins together permit the skin to stretch, then regain its original shape. With age, the skin's elastin breaks down and causes wrinkles. GAGs contain special sugars such as glucosamine hydrochloride, N-acetyl glucosamine, and glucosamine sulfate that have high water-holding properties. These are built into larger water-holding chains of sugars such as hyaluronic acid, keratin sulfate, heparin, heparin sulfate, dermatin sulfate, and chondroitin sulfate.
Proteoglycans are larger molecules with many attached GAG’s. Proteoglycans are linear GAGs made up of repeating disaccharide units composed of sugars (glucuronic or iduronic acid) and hexosamines (glucosamine or galactosamine) that are bound to a protein core. The abundance of hydroxyl, carboxyl and sulfate groups makes the GAGs intensely hydrophilic (water-loving) molecules able to form porous, hydrated gels. Hydrated GAG's cushion and provide mechanical support to tissues.
Nutrient Supplements of GAG sugars
Because of the importance of the special sugars in GAG’s, nutrient supplements
are often used. A typical daily formula would contain:
| N-Acetyl-D-Glucosamine | 250 to 500 mg |
| D-Glucosamine Hydrochloride | 250 to 750 mg |
| D-Glucosamine Sulfate | 100 to 300 mg |
Collagen and Elastin in Cosmetics Have No Effect on Skin
Collagen and elastin are often incorporated into cosmetics. This material is derived from either bovine (cattle) or avian (bird) sources. Neither collagen or elastin present in the cosmetics are able to penetrate the skin. Sometimes fragments, or digests, of these molecules are used, but these fragments also cannot penetrate the skin. These products also may expose you to the the dangers of prions, the cause of "mad-cow" disease, a condition which is characterized by progressive brain degeneration.
Other proteins, as hydrolyzates (fragments of the original protein), are often incorporated into skin and hair products. In conditioning shampoos they can help "bulk-up" the hair. However, because the original protein has been broken down, the source of the protein is of little consequence. For example, a hydrolyzate of silk proteins has no advantage over a hydrolyzate of soybean or wheat proteins. Immunologists usually consider hydrolyzates of soy proteins the safest in terms of potential allergic effects.
Sebaceous Glands and Eccrine (Sweat) Glands
The sebaceous glands are clusters of cells that produce an oil called sebum. Two or more sebaceous glands secrete sebum via minuscule tubes in the hair follicle, from which the sebum is then secreted onto the hair and the surface of the skin. Sebum helps waterproof the skin and hair. Through the course of evolution humans have lost most of their hair, yet sebum is still produced in abundance. During the teen-age years, sebaceous glands increase sebum production, which may harden into a "comedo" and block the pore opening, causing the inflammation and infection that leads to acne.
The two to three million sweat glands on your skin produce a salty, watery solution (perspiration) that is transported to the surface through coils of cells that form long, vertical channels opening at the skin's surface. Sweat glands can produce as much as 11 liters (3 gallons) of sweat daily. The sweat glands do not use the same pores as sebaceous glands, but the secretions of both glands mix on the skin's surface to create the "Acid Mantle".
"Skin pH" is a chemist's term meaning "Potential of Hydrogen" and is used to measure the degree of acidity or alkalinity in the outer layers of the skin. It is measured on a scale ranging from 0 to 14 where the center of the scale, at 7, is neutrality (neither acid nor alkaline). A reading below 7 indicates that the substance being measured is acidic and above 7 is alkaline.
The acid mantle, the combination of sebum (oil) and perspiration, on the skin's surface protects the skin and renders the skin less vulnerable to damage. It also protects from attack by environmental factors such as the sun and wind and leaves it less prone to dehydration. Normal skin pH is somewhat acidic and in the range of 4.2. to 5.6. It varies from one part of the body to another and, in general, the pH of a man's skin is lower (more acidic) than a woman's. The acid mantle inhibits the growth of foreign bacteria and fungi causing the skin to remain healthier and have fewer blemishes. Acne, allergies and other skin problems become more severe when the skin become more alkaline.
The pH system works in 10-fold multiples and each pH unit represents a 10-fold difference in alkalinity. For example, a soap with a pH of 10.5 has 10-times the alkalinity of a soap of pH 9.5. "Mild" soaps are often alkaline (pH 9.5-11), and remove the natural acid protection as well as extracting protective lipids (fats) from the skin. Irritated and eczematous skins tend to have a more alkaline pH, and washing with soap can increase this alkaline state and make the skin even more vulnerable to irritation and infection.
Human Pheromones (Sexual Attractants) and Apocrine Glands
Humans have glands at the base of the hair follicles of the skin, especially in the armpits and and the genital regions that produce odors, called pheromones, that attract the opposite sex. The active compounds causing these effects are uncertain but they appear to consist of short-chain fatty acids such as proprionic acid and butyric acid (both of which in their pure state have strong and disagreeable smells). Steroid hormones, related to androstenone, also seem to function as sexual attractants.
Human pheromones may serve more to increase feelings of comfort, pleasantness and relaxation with another person than to cause feelings of sexual attraction. One double-blinded, well-controlled study by Winnifred Cutler, a researcher in human pheromones, found that human pheromones increased the attractiveness of men to women as measured by the frequency of petting/affection/kissing, informal dating (that is, a date not arranged the day before) and sleeping with a romantic partner. However, formal dating and sexual self-stimulation was not changed. While pheromone actions exist in humans, their effect is moderate, increasing interpersonal cooperation and friendliness, and is heavily modified by other psycho-social factors (W. B. Culter, E. Friedmann, and N. L. McCoy, Pheromonal influences on sociosexual behavior in men, Archives of Sexual Behavior, Vol. 27, pages 1-13, 1998).
Does bathing remove your natural sexual attractants? Human pheromones are fatty molecules with low water solubility. Bathing and swimming in detergent-free water, saunas, and steam baths should have only a moderate effect on pheromone removal. However, heavy use of soaps and detergents could strip away your natural sexual attractants and lower your skin pheromone levels.
What happens to your skin as you get older? As the body ages, the appearance and characteristics of the skin change. Visible aging of the skin starts at about age 25 as the natural regenerative process begin to slow. The skin replaces old cells more slowly and there is a slower turnover of the surface skin and slower wound healing. After age 45, a thinning of the skin begins, due in part, to hormonal changes. This thinning make the skin more fragile and vulnerable to damage by abrasion and more sensitive to irritating environmental factors and allergens. The coils of collagen and elastin suffer cuts and crosslinking damage and as a result, the skin losses much of it's strength and elasticity. The moisture holding proteoglycans and GAGs decrease in abundance, making the skin become dryer and looser. The skin loses fat, so it looks less plump and smooth. The number of blood vessels in your skin decreases, and the skin loses its youthful color and glow.
While all these changes are taking place, gravity is also at work, pulling at the skin, causing it to sag. Wrinkles around the eyes are a characteristic signs of skin damage. The skin tends to heal more slowly and minor blemishes develop. In addition, this aging process can be exacerbated by factors such as extremes of cold or heat, excessive sun (UV radiation), psychological stress, and improper nutrition. The effects of photodamage can be seen by comparing skin in areas exposed to sun to areas usually covered. Exposed skin has mottled hyperpigmentation while the nonexposed skin is usually clearer and paler.
During aging the oil-producing (sebaceous) glands become less active, and your skin becomes drier. The skin becomes more sensitive to the use of harsh soaps and disinfectants which more easily damage skin. We have a natural oil covering our skin named sebum, which is produced by glands in the skin. When the oil is removed by frequent use of drying agents, such as soap, the skin becomes dry which can lead to cracking and flaking. Once cracking occurs the skin is susceptible to inflammation and itching. Everyday factors that may cause drying of the skin include harsh soaps, long hot baths or showers. In our modern culture, most people overdo skin cleansing.
Development of Common Skin Lesions
In addition to the general loosening or "sagging" of skin as we age, skin growths and lesions become more common. They may range from harmless "seborrheic warts", "liver spots" or "age spots" to skin cancers that require immediate treatment.
Age spots are also called liver spots, lentigo simplex and senile lentigines. They are flat, gray, brown or black spots that occur on more than 90% fair-skinned people after age 50. Age spots range from freckle-size to a few inches in diameter. They are most common on skin areas most exposed to the sun. True age spots don't become cancerous and require no treatment, but sometimes they look like cancerous growths. They can be lightened with skin-bleaching products or removed. Hydroxy acids and strong copper peptides often slowly remove these lesions. See www.scar-reduction.com.
Actinic eratosis are gray-to-pink-to-red, scaly spots called actinic keratoses. These usually occur on your face, scalp and the backs of hands. They start as flat lesions that feel like sandpaper, but later may develop a hard, wart-like surface. Between 1% to 3% can progress to skin cancers within 10 to 20 years if ignored, and may need to be removed surgically. In the early stages they can be removed by applying a chemotherapy cream or freezing with liquid nitrogen. Hydroxy acids and strong copper peptides often slowly remove these lesions. See www.scar-reduction.com. These should not be confused with skin melanomas which do not appear to be associated with sunlight exposure. See www.skinbiology.com/morehealthysuntanning.html for more information on sunlight and cancer and the possible anti-cancer effects of sunlight exposure.
These yellow to brown to black raised waxy-looking spots or wart-like growths look like they were stuck on the skin surface. Normally, seborrheic keratoses don't become cancerous, however they can resemble skin cancer and should be checked by a physician. Sometimes they may bleed if irritated by rubbing. They are more common in fair-skinned people past age 40. They are not cancerous and commonly occur with aging. They can be easily removed by freezing with liquid nitrogen (cryosurgery), scraping (curettage) or burning with an electric current (electrosurgery). Hydroxy acids and strong copper peptides often slowly remove these lesions. See www.scar-reduction.com.
These are harmless, small, bright red domes created by dilated blood vessels. They occur in more than 85 percent of people by middle-age, usually on the trunk. Electrosurgery or laser therapy removes these spots.
"Broken Capillaries" or Telangiectosia
These dilated facial blood vessels are usually related to sun damage. They respond to the same treatments as angiomes.
Skin Tags
Skin tags are small, soft, skin-colored growths that often protrude above the skin and are usually found on your armpit, neck, or groin. They are usually harmless, but can be removed by cutting, cryosurgery or electrosurgery. Hydroxy acids and strong copper peptides often slowly remove these lesions. See www.scar-reduction.com.
Shingles is an inflammation of a nerve caused by the same virus as chicken pox. Early symptoms are localized pain, headache or fatigue. Shingles can affect people of all ages, but is more common and painful in older adults.
These are enlarged leg veins that appear blue and bulging. They are common in older individuals. The veins become twisted and swollen when blood returning to the heart against gravity flows back into the veins through a faulty valve. This condition is rarely dangerous.
Laser therapy may remove smaller varicosities. More severe cases can be treated with surgery or injections.
Skin Damaging Eczema and Dermatitis
The terms dermatitis and eczema are often used synonymously and authorities generally disagree on a differences in the two terms.
The word eczema is used to describe all kinds of superficial skin inflammation characterized by redness, blistering, oozing, edema, scaling, crusting, brownish-lesions, thickened skin, and itching skin conditions. Examples of eczema include dermatitis, allergic contact eczema, seborrheic eczema, and nummular eczema. These condition may cause skin disfigurement, rashes, and uneven pigmentation.
Atopic Dermatitis or Atopic Eczema
The word "atopic" describes a group of allergic or associated diseases that often affect several members of a family. These families may have allergies such as hay fever and asthma but also have skin eruptions called atopic dermatitis. While most people with atopic dermatitis have family members with similar problems, 20% may be the only one in their family bothered by this problem. Atopic dermatitis is very common in all parts of the world. The skin on the feet and hands can become very itchy and can be produce visual skin blemishes and marks.
Contact dermatitis is caused by allergens or irritants --caustics, strong soaps, detergents, organic solvents, vacuum cleaner dust, and topical drugs. Your dermatologist will use patch-tests to provide evidence of sensitivity to various allergens and irritants.
"Housewives' eczema," is frequently seen in housewives and other "wet workers". It is worsened by washing dishes, clothes, and babies, and repeated exposure to detergents, water or prolonged sweating under rubber gloves.
Dandruff, Seborrhea and Seborrheic Dermatitis
Various dermatitises can produce skin damage and undesirable skin lesions. Dandruff is characterized by excessive scaling on the scalp without redness. There is no skin inflammation. Seborrhea describes excessive oiliness of the skin, especially of the scalp and face. There is no redness or scaling. Patients with seborrhea may later develop seborrheic dermatitis.
The signs of seborrheic dermatitis is an inflammation in areas having the greatest number of sebaceous or oil glands. The scalp, sides of the nose, eyebrows, eyelids, and the skin behind the ears and middle of the chest are the most common sites. The affected skin is reddish and can have greasy-looking, often yellow “scales" on the skin. Itching may occur but is usually mild. Special shampoos are used to successfully treat seborrheic dermatitis, but it tends to recur.
Seborrheic dermatitis is more common in people with oily skin or hair. There is some evidence that a skin infection with a yeast-like organism play a role in this disorder and antibiotics to control such yeast are being tested for treatment.
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