Behavior of Normal Skin

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Chapter 1Behavior of Normal

Healthy Skin

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t is the desire o all to possess healthy normal skin. However, it is uncertainexactly what constitutes normal skin. Skin is an irregular surace composedo skin scales with intervening hairs, sweat ducts and oil glands that reflect

light to the eye, which is perceived as beauty. Healthy skin is important, ashumans assess each other based on skin appearance beore any other attribute.Skin appearance is the result o many interrelated biochemical and physicalactors. Unortunately, throughout time, these actors are subject to changesrom both internal aging and external actors. Sun, smoking, stress, diseaseand aging alter the structure o the skin, making it sag, and lose its lusterand suppleness. Proessional skin care maintains skin in its most attractiveand healthy state. Tis chapter will provide an understanding o normal

skin behavior in relation to its structure and unction to maintain a healthyappearance or a lietime.

Skin structure ________________

Ep id e rm is ________________________________________

Te skin is composed o two layers, the epidermis and the dermis, eachwith a distinct unction. Te epidermis is the outer skin layer that orms a

The two layersof the skin arethe epidermis,or outer skin,and dermis, or

inner skin.



Behavior of Healthy Normal Skin Physiology of The Skin, Third Edition

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barrier to the outer world. Tis barrier keeps out water, sunlight, insects, germs,heat and cold, dirt and gases. It keeps in fluids such as water and blood, and

holds sae minerals, vitamins, hormones, proteins and heat. An incrediblesel-renewing system, the epidermis provides replacement o the outer cellslost to the environment. It provides a waterproo outer layer, yet permitsinternal water to carry nutrients to the outermost living cells. It provides atough outer layer to resist riction, abrasion and pressure, yet is sensitive tothe lightest touch or sofest breeze. Less glamorous, but equally as important,the skin serves as a vast waste disposal system, ridding the body o many toxicsubstances. (See Figure 1-1.) 1–2

Fig ure 1-1. The st ruc tu re o f the sk in . The sk in is c o m p osed o f the ou te r la yer know n

a s the ep id e rmis; an d the inne r la ye r, know n a s the d e rmis. The sk in b a r rie r is

essen t i a l t o sk in he a lt h a nd m ust b e p rese rved to p reven t d isea se .

Derm is: Pa p i lla ry d e rm is __________________________Te outer epidermis is tightly connected to the underlying inner skin,

known as the dermis. Te dermis accounts or more than 90% o the skinmass and or the greatest part o its physical strength. Te major divisions othe dermis are the papillary dermis and the reticular dermis. Te papillary



Draelos and Pugliese Chapter 1

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dermis is the outer portion o the dermis in direct contact with the epidermis.It is thin, contains small and loose fibers. Te protein fibers that make up the

main constituent o the skin are collagen fibers. Tese collagen fibers are madestretchy and resilient by the addition o elastic material, known as elastin. Inaddition, there are number blood vessels in the papillary dermis to providenutrition and lymphatic vessels to carry away the wastes o the body. Finally,there are connective tissue cells and glycosaminoglycans in the papillarydermis. It is the source o nutritional support or the epidermis.

De rm is: Re t ic ula r d e rm is __________________________

Te reticular dermis lies under the papillary dermis and has ewer cells,relatively ew blood vessels, dense collagen bundles and coarse elastin fibers.Tis layer provides the physical strength to the skin that resists tearing. It isthe reticular dermis rom animals that provides the strong leather used inpurses, luggage and shoes. Within the reticular dermis are the sweat and oilglands, along with the hair ollicles, that are collectively known as the skinappendages.

Stratum corneum __________

Perhaps the most importantlayer o the skin, rom a cosmeticstandpoint, is thestratum corneum

(SC), also known as the “hornylayer.” Tis outermost layer o the

epidermis is impacted by cleansing,moisturization and skin care treat-ments to the greatest degree. It is thelayer assessed by the eye to arrive at theimpression o lovely skin. Consider thatthe whole epidermis is only 0.04–1.5 mm (millimeters) thick; the SC is only15–150 microns thick. o put that into perspective, the paper on which this iswritten is 70 microns thick. A micron is 1/1,000 o a millimeter; a millimeteris 0.039 inches. Te SC is 0.0030 inches thick. Tat is thinner than a humanhair. Most o human lie hangs upon this thin structure, or without a SC,the epidermis would perish. While the SC is very thin, it also is a very toughlittle tissue. Here is why. Look at the diagram o the stratum corneum under

high magnification in Figure 1-2.

The stratum corneumis the nonlivingspecialized outer layerof the epidermis thatprovides a protectivecoating over the bodyand is manipulated by

skin care products.



Behavior of Healthy Normal Skin Physiology of The Skin, Third Edition

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Fig ure 1-2. A d ia g ra m o f t he st ra t um c o rneum und e r h ig h m a g n ific a t io n .

A d a p

t e d f r o m a

P fi z e r

I n c .

i l l u s

t r a

t i o n

b y

J .

E .

M c

K i e .

Cross Section of Human Skin (Magnified 25,000 times)

Stratum corneum

Viable epidermis

Dermis

Subcutaneoustissue

25,000x

000

0.5

1090

125x

Keratin is the protein that makes up the bulk o the SC. Keratin is a helical,

or coil-shaped fibrous protein made up o a series o building blocks, knownas polypeptides. Tese polypeptides are, in turn, made up o the most basicsubstances, known as amino acids. Amino acids are arranged in a variety oorders to orm chains o polypeptides, which are then twisted around eachother to orm proteins. Tese polypeptides vary in different parts o the bodyso that the skin protein is not homogeneous, but rather heterogeneous. Teprotein is resistant to water and many chemicals. It is this complex structurethat provides part o the protection rom the outside. Manuacturing proteins

is one o the major unctions o the skin.Tese keratin proteins are ormed and arranged into cells known ascorneocytes that are held together with ats, known as lipids. Te SC canbe thought o as a brick wall, with the protein-rich corneocytes orming thebricks and the lipids unctioning as the glue. It is this brick wall that providesthe barrier necessary or the beauty and health o the body.

Te lipids that keep the proteins glued in place in the SC are water-insoluble,oily substances. Tey can be classified by their electrical charge and by theirstructure. Te two major groups o lipids are polar lipids and nonpolar

lipids. Polar lipids have an electrical charge. Examples o this type o lipid arephospholipids,glycolipids andcholesterol. Non-polar lipids have no electricalcharge. Triglycerides, squalene and waxes are examples o this group.

Te six major structural groups o lipids are: triglycerides, the mostabundant lipids in the body, which unction as energy storage compounds



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and make up between 12–25% o the lipids in the SC; atty acids, which givethe oily eel and make up between 12–20% o the lipids in the SC; waxes,

which make up 6% o the lipids in the SC; and cholesterol, sphingolipids andceramides, which make up between 14–25% o lipids in the SC.

Making of the barrier _____________________________

Here are the mecha-nisms, outlined briefly, thatmake up the final SC cell(See Figure 1-3.) Te cells

are called keratinocytes until they are finally corni-fied at which time they arecalled corneocytes. Followthe process in Figure 1-4 showing the various layers

o the skin.he basal layer, or

bottom layer, is the active,growing, dividing layero the epidermis. Eachcell divides under controlo a very sophisticatedbiochemical system. As

Stratum corneum

Stratum lucidum

Stratum granulosum

Stratum spinosum

Stratum ba sale

Fig ure 1-3. The st ra tum c o rneum . The st ra tum

c o rneum i s m a d e t h roug h a c om p le x p ro c ess t ha t

c ha ng es the c e lls in to a p ro te in she l l.

Fig ure 1-4. M a g n ified st ra t um c o rneum .

A d a p

t e d f r o m a

P fi

z e r

I n c .

i l l u s

t r a

t i o n

b y

J .

E .

M c

K i e .

Stratum Corneum Cells (Magnified 102,000 times)

Surface of Skin Surface of Skin

102,000x

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Behavior of Normal Skin