Anatomy and Physiology
of the Skin
Image from: http://www.chiff.com/health/skin.htm
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- 1© The East-West School for Herbal and Aromatic Studies and Jade Shutes
Table of Contents
Overview of the Integumentary System................................................. 4
Understanding the Skin.......................................................................... 4
The Epidermis........................................................................................ 6
The Acid Mantle..................................................................................... 6
What is pH?............................................................................................ 7
The Five Layers of the Epidermis.......................................................... 8
Stratum basale........................................................................... 8
Stratum spinosum...................................................................... 10
Stratum granulosm.................................................................... 11
Stratum lucidum........................................................................ 11
Stratum corneum....................................................................... 11
Lipids and the Skin barrier function..................................................... 11
Transepidermal water loss and NMF...................................................... 13
How to protect the skin from moisture loss............................................ 14
The basement membrane/dermoepidermal junction.............................. 14
The Dermis............................................................................................. 15
Structures in the Dermis......................................................................... 16
What happens as our skin ages?............................................................. 17
Accessory structures of the Skin............................................................ 18
Hair, Hair follicles and Sebaceous Glands................................ 18
Sebaceous lipids......................................................................... 18
Overview of lipid composition/sebum/epidermis...................... 19
The sudoriferous glands............................................................. 19
Sensory nerves, Nails................................................................. 20
Clues the nails provide............................................................... 21
The Hypodermis/subcutanea.................................................................. 22
Essential Oils as novel skin penetration enhancers................................ 23
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- 2© The East-West School for Herbal and Aromatic Studies and Jade Shutes
Learning Objectives
After you have completed this section, you will be able to:
1. List and discuss the 7 functions of the skin.
2. Define the term ‘Acid Mantle’ and explain its structure and function.
3. Describe the general structure and function of each of the five layers of the
epidermis.
4. Name and describe the 4 types of cells found in the epidermis.
5. Discuss the importance of the Langerhans’ cells.
6. Define and explain the importance of: the acid mantle.
7. Define the term pH and its relevance to the skin and skincare products.
8. Describe the importance of the stratum corneum in relation to transepidermal
water loss and the natural moisturizing factor.
9. Describe the role of ceramides, cholesterol, and fatty acids in the health of
the skin.
10. Identify the primary function of the dermis.
11. List and describe the two layers of the dermis and the structures it contains.
12. Describe what happens as the skin ages.
13. Explain the importance of sebum and describe the lipids it contains.
14. Provide an overview of health clues the nails can provide.
15. Define and provide functions of the hypodermis.
16. Describe the difference in the subcutaneous layer in men versus women.
17. Describe how essential oils are novel penetration enhancers.
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- 3© The East-West School for Herbal and Aromatic Studies and Jade Shutes
Overview of the Integumentary System
The integumentary system is the largest system of the body. It makes up approximately 16%
of body weight, is 1.5 - 2 square meters in area and consists of the largest organ of the body,
the skin, and the accessory structures: sebaceous and sudoriferous glands, hair and nails. The
integumentary system is a dynamic interface between the continually changing external
environment and the body’s internal environment and helps to maintain homeostasis. 1
The functions of the integumentary system include:
• protects underlying tissues and organs from chemicals, microbes, and shock/
impacts
• maintains body temperature by insulation (heating) and by sweat evaporation
(cooling)
• synthesizes and stores vitamin D (converted to calcitriol for calcium regulation)
• protects the body from ultra violet damage
• stores lipids in the dermis
• sensory reception: touch, pressure, pain and temperature
• detoxes/excretes organic wastes, salt and water
Understanding the Skin
The skin is our largest, vital organ, maintaining our health and well being in an amazing
variety of ways. It covers an average of eighteen square feet and weighs about seven to eight
pounds. In a square centimeter of skin there are one hundred sweat glands, twelve feet of
blood vessels, and hundreds of sensory receptors for touch, heat, and cold.
Unbroken, the skin’s primary function is to serve as a protective barrier, guarding against
both foreign invasions (bacteria/fungi) and preventing excessive water and extracellular fluid
loss. The skin also protects underlying structures and organs.
The skin regulates body temperatures by constricting blood vessels and driving blood inward
in cold temperatures to preserve body heat and producing sweat in warm temperatures to cool
the body by water evaporation.
The skin is our largest sensory organ, sending neurological messages about touch, pressure,
pain, and temperature stimuli to the brain. Indeed, sensation is a very important function of
the skin.
The skin detoxifies the body by excreting wastes (mostly through the sweat glands), breathes
(takes in oxygen and releases carbon dioxide), synthesizes and stores vitamin D, and protects
the body from ultra violet damage from the sun by producing melanin (a tan). The skin is
capable of absorbing fat soluble nutrients such as vitamins A, D, E, and K.
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- 4© The East-West School for Herbal and Aromatic Studies and Jade Shutes
The skin also serves as a part of the body’s immune system, primarily by means of the rich
network of lymph vessels, and also by means of chemical constituents (i.e. Langerhan’s cells)
of the skin tissue itself. As a metabolic organ, the skin is involved in the metabolism, storage,
and catabolism of fat, and in adjusting the body’s levels of water and salt through
perspiration.2
The skin functions in homeostasis via its protective function, through regulating body
temperature, sensory perception, water balance, synthesis of vitamins and hormones, and
absorption of nutrients and other materials necessary for its health.
The skin can be considered a dynamic organ, ever changing as old cells fall away and new
cells are born. From infancy to adulthood and into old age, the skin changes in its size, shape,
qualities, and functions according to the demands placed on it.3
A cross section of the skin reveals three defined layers: the epidermis (composed of 5 layers),
the dermis (composed of 2 layers), and the subcutaneous layer. Together, these three layers
form the miraculous “living fabric” known as skin. As we study the layers of the skin, it is
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- 5© The East-West School for Herbal and Aromatic Studies and Jade Shutes
important to remember that one layer cannot be affected without some effect on the other
layers.4 The three layers of the skin represent one whole system.
The Epidermis
The epidermis is the outermost layer of the skin, known as the cuticle or protective layer and
is composed of tightly packed, scale-like avascular (not associated with or supplied by blood
vessels) stratified squamous epithelial cells which are continually being shed. Because the
cells are avascular, they depend on nutrients and oxygen diffused from capillaries in the
dermis.
The epidermis is is composed of four types of cells: keratinocytes (90%), melanocytes (5%),
merkel cells (6-10%), and Langerhans cells (2-5%).
The whole epidermis is about 0.04 - 1.5 mm (millimeters) thick depending on location. There
are two types of skin: thick and thin. Thick skin has 5 layers and is found on the palms of the
hands and the soles of the feet. Thin skin has 4 layers and covers the rest of the body.
An entirely new epidermis is formed by the migration of cells from the innermost layer of the
epidermis to the outermost layer. This takes approximately twenty-eight to thirty days, a rate
that slows down with age. Exfoliation can be beneficial in removing dead surface cells and
speeding up replacement of new cells.
The Acid Mantle
The epidermis is covered with a thin layer of natural lipids (oil known as sebum produced by
the sebaceous glands and a tiny amount of lipids from the stratum corneum) and perspiration
(sweat produced by sweat glands). This covering is called the acid mantle. The acid mantle
has an average pH of 4 to 6.5 which is designed to protect the skin against bacterial and
fungal infection as well as water loss. The acid mantle also supports the barrier function of
the stratum corneum.
If the acid mantle loses its acidity, the skin becomes more prone to damage and infection as
well as irritation and sensitivity. Soap products tend to be highly alkaline which is actually
neutralizing our skins acid pH thereby stripping away our natural defense systems. This
stripping on the skins natural protective coating can lead to a wide range of disorders and can
aggravate existing disorders (e.g. acne). This stripping also disturbs the stratum corneum’s
barrier function leading to disorders characterized by inflammation and dryness.
Kusmirek points out that the skin’s acid mantle is vital to the skin’s health as it is our first
line of defense against germs and contains elements that maintain crucial moisture.
According to Kusmirek, vegetable oils support this crucial system. 5
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- 6© The East-West School for Herbal and Aromatic Studies and Jade Shutes
To maintain the skins acid mantle:
• Avoid harsh soaps.
• Moisturize skin frequently with a slightly acidic moisturizer.
• Use pH balanced skin care products.
• Protect skin from sun as appropriate.
What is pH?
pH is the measure of acidity or alkalinity of body fluids and/or skin
products. pH is measured on a scale of 1 to 14, going from acid (1) to
alkaline (14).
1_______________________7_______________________14
Acidic
Neutral
Alkaline
Water has a neutral pH of 7. The pH of the skin is slightly acidic ranging
from 4 to 5.5. The skin, therefore, needs more neutral to acidic pH
products. Alkaline soaps/cleansers can disturb and even destroy the acid
mantle layer making the skin more susceptible to bacterial invasion and
irritation.
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- 7© The East-West School for Herbal and Aromatic Studies and Jade Shutes
The five layers of the epidermis, starting at the base of the epidermis
include:
• The stratum basale (syn.
germinativum)
The stratum basale is the deepest
layer of the epidermis and is
composed mainly of dividing and
non-dividing keratinocytes, also
called germinative or basal cells.
These cells are firmly attached to
the basal lamina, the upper layer
of the dermoepidermal junction
(to be discussed shortly), by
hemidesmosomes (half
desmosomes). Hemidesmosomes
(hemi·des·mo·somes) are
involved in promoting the
adhesion of epithelial cells to the
underlying basement membrane
thus ensuring a strong bond
between the epidermis and the
dermis. They also play a role in
tissue integrity. Over the past
10-15 years, advancements in the
study of hemidesmosomes have
shown that the absence or defects
of hemidesmosomal proteins
result in devastating blistering
diseases of the skin.
Dermal projections called dermal papillae extend upward from the dermis between
adjacent epidermal ridges of the stratum basale. The epidermal ridges are what gives each
of us our unique fingerprints. This combination of dermal papillae and epidermal ridges
increases the surface area for diffusion of nutrients between the dermis and epidermis.
The stratum basale is the main layer of the epidermis where keratinocytes undergo cell
reproduction (mitosis). This layer is only one cell thick and contains about 14% oil (mostly
phospholipids and cholesterol) and 70-90% water.
Other cells found in the stratum basale include: melanocytes and merkel cells.
• Melanocytes are spidery black cells that produce the brown-to-black pigment known as
melanin. Melanin in the epidermis gives the skin its color and also protects the
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- 8© The East-West School for Herbal and Aromatic Studies and Jade Shutes
underlying layers from the damaging effects of the sun. They make up approximately 5%
of the cells in the stratum basale.
The skin protects itself from the sun in two ways: by initiating the thickening of the
stratum corneum, and in the formation of melanin. Melanin, by providing a protective
pigment covering for the nuclei of the cells within the deeper epidermal layers, shields the
cells genetic material (DNA) from the damaging effects of ultraviolet radiation.
Melanocytes make the melanin, but they don’t retain it for long. Instead, they pass
it to the neighboring keratinocytes which then carry it up through the layers and
out of the system. Melanocytes have long and extensive processes that reach out
and contact many keratinocytes, to facilitate pigment transfer. In places where
melanocytes are concentrated and/or very active, localized deep pigmentation
occurs. (Caceci, nd)
The skin also contains varying amounts of the orange-yellow pigment, carotene, which can
be converted to vitamin A to support the health of the skin tissue as well as for the synthesis
of photoreceptor pigments in the eye. Individuals of Asian decent will have an abundance
of carotene, providing them with their unique yellow-tan skin.
• Merkel cells make up about 6-10% of the cells in the epidermis and play a role in
sensory perception. These cells work in conjunction with sensory nerve endings. Within
the epidermal and dermal junction, merkel cells form sensitive touch receptors called
Merkel discs. They can be isolated or grouped together in clusters called Merkel
corpuscles. They serve as mechanoreceptors and are involved in light touch sensation.
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- 9© The East-West School for Herbal and Aromatic Studies and Jade Shutes
• The stratum spinosum (spiny layer)
The stratum spinosum is also known as the spiny cell layer due to the tiny fibrils that
connect the cells together. These cells are called desmosomes, which are specialized cells
responsible for cell-to-cell adhesion and are found in all layers of the skin but are most
numerous in the stratum spinosum. The desmosome is an adhesive intercellular junction
that is crucial to tissues, such as the skin, that experience mechanical stress.
The stratum spinosum is eight to ten layers thick. As cells arrive in the stratum spinosum,
they have lost some of its oil and water content. Limited mitosis can occur at this stage.
Langerhans cells are found in the stratum spinosum. Langerhans cells are phagocytic cells
(cells that ingest and destroy foreign matter, such as microorganisms or debris)
manufactured in the bone marrow. Langerhans cells make up 2-5% of the cells of the
epidermis. They play a role in immunity by detecting foreign substances, also called
antigens. Antigens include bacteria, fungi, virus, or other harmful substances. Langerhans
cells are found mainly in the stratum spinosum and stratum germinativum layers of the
epidermis, though they can also be found in other organs throughout the body. Langerhans
cells seem to be present in lymphatic nodes as well.
These cells participate in the cutaneous immune response and migrate from skin to lymph
nodes.6 Research at Harvard Medical School has shown that one of the most important
events in skin aging is a decrease in the proliferation of Langerhans cells.
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- 10 © The East-West School for Herbal and Aromatic Studies and Jade Shutes
These immune system cells send dendrites to the very surface layer of the stratum corneum
where they are exposed to everything happening at the surface and come into contact with
everything applied to the skin. Langerhans’ cells are involved with the skin’s reaction, such
as in dermatitis or sensitization. Materials aimed at activating the skin’s natural defense
system can have truly far-reaching effects. And these are capabilities that have long been
claimed for aromatherapy.
• The stratum granulosm (granular layer)
Here in the stratum granulosm cells stop dividing and begin producing large amounts of the
protein keratin (KER-a-tin). Keratin is extremely durable and water-resistant. It is also the
protein that forms the basic structure of hair and nails. The stratum granulosm is one to four
cellular layers thick consisting of flattened rows of cells.
• The stratum lucidum
The stratum lucidum, also called the ‘clear layer’, is found only in the thick skin of the
palms of the hands and soles of the feet. It is thin and poorly defined, varying in thickness
from one cell to noticeable thickness on the palms of the hands and the soles of the feet. It
is composed of flattened and hardened skin cells (non-living) made of keratin, similar to the
stratum corneum.
• The stratum corneum (hornlike layer)
This is the layer of the epidermis that is exposed to the environment and is the thickest of
the epidermal layers having 15-30 layers of keratinized cells which are continuously being
shed. The cells that make up this layer have lost most of their oil and water content
(compared to the stratum germinativum layer). Although the water content is different from
the stratum germinativum layer, the stratum corneum maintains up to 15-30% water which
is vital to enabling the stratum corneum to work.
Keratinocytes into Corneocytes
Recall that keratinocytes are formed in the stratum basale and migrate upwards through the
layers of the skin. As they proceed through each layer they become flattened and filled with
keratin. Once they reach the stratum corneum they have changed into dead keratinized cells
with no nucleus. These cells in the stratum corneum are called corneocytes. The process of
keratinocytes transforming into corneocytes is know as epidermal differentiation.
Lipids and the Skins Barrier Function
The stratum corneum is said to have a ‘brick and mortar’ design. The bricks are the cells
(corneocytes) that make up this layer while the mortar is the complex of intercellular lipids
that hold or bind moisture in between the ‘bricks’. Lipids are produced during the process
of epidermal differentiation and originate from lamellar bodies (small secretory cells that
are found in keratinocytes) that are expelled from keratinocytes in the stratum granulosum.
As the differentiation process nears its end, the lamellar granules discharge their contents
into the intercellular space. The lamellar granules deliver both lipids and a number of
hydrolytic enzymes. These enzymes act on phospholipids 7 in the vicinity of the stratum
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granulosum-stratum corneum interface resulting in the production of the principal lipids of
the stratum corneum. 8
The principal lipids found in the stratum corneum include ceramides (approx. 40-50%),
cholesterol (20-25%), fatty acids (10-25%). It is this mortar of lipids that serves to prevent
water loss through the stratum corneum.
Ceramides are a type of sphingolipid, and they are responsible for generating the stacked
lipid structures that trap water molecules in their hydrophilic region. These stacked lipids
surround the corneocytes and provide an impermeable barrier by preventing the movement
of water and NMF out of the surface layers of the skin.9 Cholesterol is the most abundant
individual lipid in the stratum corneum. The role of cholesterol in the epidermal barrier is
probably to provide a degree of fluidity to what could otherwise be a rigid, possibly brittle
membrane system.10
Fatty acids in the skin provide lubrication, softening and protection for the protein
structures and prevention of moisture loss from the skin. Both essential and non-essential
fatty acids play separate and critical roles in proper skin function. Some of the fatty acids
found in the skin include: palmitic acid, palmitoleic acid, myristic acid, stearic acid,
linoleic acid and others. Linoleic acid (LA), the most abundant polyunsaturated fatty acid
(PUFA) present in the epidermis.11
Linoleic acid is an essential fatty acid in the skin that is required for the formation and
maintenance of the cutaneous barrier to water loss. 12 It is crucial to the proper growth and
development of the epidermis. It also is required for synthesis of the important long-chain
ceramides necessary to protect against dry skin.13 Vegetable oils rich in linoleic acid
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- 12 © The East-West School for Herbal and Aromatic Studies and Jade Shutes
include: safflower, sunflower/not high oleic acid version, flax seed, hemp seed, wheatgerm,
walnut, and sesame oil. Macadamia nut and sea buckthorn oils are all rich in palmitic acid.
Deficiency of essential fatty acids in the skin alters the barrier function of the skin, disrupts
epidermic homeostasis, and can lead to marked skin abnormalities, including excessive
epidermal water loss, dryness, scaliness, redness, dermatitis, and other signs of
inflammation.14 EFA deficiency may arise from various factors such as insufficient supply
in the diet, and metabolic anomalies, such as advanced age and certain diseases including
diabetes. The topical application of vegetable oils rich in essential fatty acids can be of
great benefit in restoring the skin barrier as well as in treating inflammatory disorders
including eczema, dermatitis, and psoriasis, for wound healing and preventing wrinkles.
Corneocytes in the stratum corneum, therefore, are cells encased in a protein and lipid
matrix and it is this extracellular lipid matrix that provides the barrier functions of the skin.
This is considered to be one of the major functions of the skin. By providing a physical
barrier, the stratum corneum prevents the absorption of noxious substances and the entry of
pathogens (microbes), as well as prevents excessive water loss. This protective barrier
function is principally the role of the epidermis and specifically of the stratum corneum.
Transepidermal water loss and the natural moisturizing factor
The stratum corneum plays a key role in maintaining the water level of the skin below and in
regulating the natural moisture flow out from the deeper layers to be lost eventually by
evaporation from the skin surface. This flow is known as the transepidermal water loss
(TEWL). The stratum corneum plays a vital role in controlling and reducing TEWL. With
the brick-and-mortar design, the cells in the stratum corneum (the corneocytes) form a waterretaining barrier embedded in a lipid matrix.
The lipids and the natural moisturizing factor (NMF) of the stratum corneum are crucial in
maintaining the water level of the skin as well as reducing transepidermal water loss. The
NMF is a collection of water soluble compounds (such as free amino acids, urea, lactic acid,
sugars, peptides, etc) that are only found in this layer. These compounds are responsible for
keeping the skin moist and pliable by attracting and holding water. NMF components are
hydrophilic and act as humectants attracting and absorbing water. They can hold large
amounts of water in the skin cells and are also capable of absorbing water from the
atmosphere and/or products applied to the skin. The lipids serve to prevent water loss from
occurring in the NMF.
If the water content of the stratum corneum (commonly caused by a breakdown or
assault to the skin barrier) falls below 10% the natural functions of it are impaired
and the skin becomes dry (dehydrated), scaly, and less pliable, all the signs of xerosis
(an abnormal dryness of the skin or mucus membranes). The most common areas
individuals experience xerosis are on the arms and legs.
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Cold or heat exposure (such as sunburn, wind burn, frostbite), ambient low humidity, heating
during the winter months, age, genetics, seasonal influences and diet affect the stratum
corneum lipids with any deficiency in these lipids potentially resulting in dehydrated skin or
xerosis. The use of solvents, detergents, excessive use of water and soap, and other irritating
chemicals can break down the protective lipid layer and increase transepidermal water loss
by altering the skins natural water-holding capacity.
Signs of a compromised skin barrier include: dry, itchy, flaky, rough, and dull skin. The skin
may also have fissures and cracks. The maintenance of a healthy skin barrier is essential,
especially for those individuals who suffer with common skin disorders that can be
exacerbated by dry skin, e.g. psoriasis, atopic dermatitis and photodamage. All of these
disorders can be linked to fundamental barrier dysfunction, which makes the skin vulnerable
to environmental insults that cause dryness and irritation. Maintaining healthy skin on a daily
basis is crucial for adults and children even in the absence of such disorders.15
How to protect the skin from loss of moisture
and support lipid matrix
The term emollient is derived from the Latin meaning to soften and
implies a substance that acts to smooth the skin surface. Emollients
soften the skin, prevent TEWL, and support the lipid matrix.
Emollients include vegetable oils, creams, lotions, ointments, butters,
and balms.
Substances such as beeswax, squalene, lanolin, shea butter, avocado
oil, and other vegetable oils provide valuable nutrients to the skin and
are also slightly occlusive. Occlusive substances have a ‘hydrating
effect on the skin because they form a barrier on the skin’s surface,
which helps to reduce the evaporation of water from the
skin” (Howard, 2005).
Humectants are substances which attract water. Honey and glycerin
are the two most common humectants used in creams, lotions and in
water based preparations.
The Basement membrane/Dermoepidermal junction
At the bottom of the epidermis is a very thin membrane, called the basement membrane or
the dermoepidermal junction, which attaches the epidermis firmly, though not rigidly, to the
dermis.
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The dermoepidermal junction is an undulating basement membrane that adheres the
epidermis to the dermis. It is composed of 2 layers, the lamina lucida and lamina densa.
The lamina lucida is thinner and lies directly beneath the basal layer of epidermal
keratinocytes. The thicker lamina densa is in direct contact with the underlying dermis.16
Dermal papillae from the papillary dermis contain a plexus of capillaries and lymphatics
oriented perpendicular to the skin surface. These fingerlike projections are surrounded by
similar projections of the epidermis. This highly irregular junction greatly increases the
surface area over which exchange of oxygen, nutrients, and waste products occurs between
the dermis and the avascular epidermis. As the skin ages, the dermoepidermal junction
flattens and is responsible for some of the visible signs of aging.
The Dermis
The primary function of the dermis is to sustain and support the epidermis by providing
physical and nutritional support. The dermis accounts for more than 90% of the skin mass
and for the greatest part of its physical strength. 17 The two layers of the dermis are the
papillary layer, the outermost layer in direct contact with the epidermis, and the reticular
layer.
The papillary layer (stratum papillarosum) is thinner, consisting of loose connective tissue
containing capillaries, elastic fibers, reticular fibers, and some collagen. It accounts for about
1/5th of the dermis. It contains lymphatics and sensory neurons. This is the layer of the
dermis that is in contact with the epidermis. The papillae (projections) of this layer form the
base for the friction ridges on the fingers and toes.
The reticular layer (stratum reticularosum), on the other hand, is thicker and has dense
collagen bundles and coarse elastin fibers and it carries most of the physical stress of the
skin. The reticular layer also contains fibroblasts, mast cells, nerve fibers, lymph vessels, and
epidermal appendages (hair follicles, sebaceous glands and sweat glands). This layer is able
to stretch (e.g. during pregnancy or obesity), however, when stretched too far it causes
‘tearing’ of the dermis. The repair of this tearing is what leaves stretch marks on the skin.
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Structures in the Dermis
• The fibroblast
The fibroblast is the major cell type of the dermal layer of the skin. These cells produce and
secrete procollagen and elastic fibers. Procollagen is terminally cleaved (having to do with
the appearance of cells when viewed under a microscope. The nucleus of cleaved cells
appears divided or segmented.) by proteolytic enzymes (any of a group of enzymes that break
the long chainlike molecules of proteins into shorter fragments) into collagen that aggregates
and becomes cross linked. The fibrous protein collagen, the major constituent of skin and
bone, is derived from procollagen, a soluble precursor.
• Connective tissue
Connective tissue is the material inside the body that supports many of its parts. It is the
“cellular glue” that gives your tissues their shape and helps keep them strong. It also helps
some of your tissues do their work. Connective tissue gives the skin strength, resiliency, and
flexibility.
This network of connective tissue in the dermis is not only responsible for the resiliency and
adherence of the skin, it also contains the main mechanism for the healing of injuries of all
kinds. Connective tissue webbing of the dermis is also responsible for the changes in
appearance of aging skin as well. 18
There are three types of fibers that make up the connective tissue (fibrous material) in the
dermis: elastin, collagen, and reticulin. Elastin is a protein component of the fibers that give
the skin its elasticity—the ability to stretch and return to it original shape. Collagen is a
complex, long chained protein that is tough and does not stretch easily. It gives the skin
strength and makes up about 75% of the fibrous material. Reticulin is the least understood of
these fibers and is present in the smallest amount. It is similar to collagen, made of small
protein fibers, and appears mainly in the papillary layer. It is believed that the fine meshwork
of reticulin fibers supports cells or groups of cells which have specialized functions.
The connective tissue fibers are supported in a gel-like substance composed mostly of
mucopolysaccharides, particularly hyaluronic acid. Hyaluronic acid attracts and retains
water to maintain moisture and flexibility in the skin. Hyaluronic acid can hold a thousand
times its weight in water, which helps keep the skin tissues well hydrated (Howard, 2005).
This hydration keeps the collagen and elastin fibers pliable. Hyaluronic acid diminishes with
age.
• Blood and lymph vessels
The dermis is well supplied with blood vessels, both arterioles and capillaries that originate
from arteries and veins in the subcutaneous layer. Blood vessels within the dermis supply
nutrients to the stratum basale as well as to the cellular structures of the dermis such as
glands and hair follicles. The dermal blood vessels play an important role in regulating body
temperature and blood pressure.
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Lymph vessels
Lymph vessels take up fluid from the capillaries that has been diffused but not reabsorbed by
them. In the skin, lymphatics carry material that has penetrated the dermis, including solvents
of skin cosmetics, injected vaccines or drugs, stains from tattoos, and products of
inflammatory reactions. Once the initial lymphatics drain the fluid into the contractile chain
of lymphangions (functional unit of the lymph vessel), peristaltic motion coupled with
regular valve closure to prevent reflow provides an active mechanism to propel fluid toward
the central ducts.19 Gentle facial massage can support healthy lymph flow in the skin.
What happens as our skin ages?
Most of the issues we experience as we age occur in the dermis and are a result of
nutritional, environmental and cosmetic issues as well as the aging process itself.
During the aging process:
• Collagen fibers decrease in number & stiffen
• Elastic fibers become less elastic
• Fibroblasts decrease in number
• Langerhans cells and macrophages decrease in number and become less-efficient
phagocytes
• Oil glands shrink and the skin becomes dry
• Walls of blood vessels in dermis thicken so decreased nutrient availability leads
to thinner skin as subcutaneous fat is lost
These details greatly support the need to maintain and support the health of the skin
through the application of organic whole skincare products, whole foods/good
nutrition, clean air, and a healthy emotional environment.
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Accessory structures of the Skin
The accessory structures of the skin include hair,
hair follicles, sebaceous glands, sweat glands and
nails. The are located in the dermis and project out
on the skin surface.
• Hair
With the exception of the palms of the hands, the
soles of the feet, the lips and portions of external
genitalia, the human body is covered with hair. The
primary function of hair is to protect and insulate.
Hair in the nose and the eyelashes serve to prevent
particles and insects from entering. Hair is also a
distinguishing characteristic to each individual and can serve as a sexual attractant. It can also
be a source of psychological stress.
• Hair follicles
Extending from deep in the dermis to the surface of the skin, the hair follicle is a tubular
structure that is lined with epithelial tissue and houses the growing hair. The only muscle in
the skin is the erector pili muscle which is attached to each hair follicle. It causes the hair to
stand on end, reacting to cold or emotion. *The hair follicle is considered to be a site of
entrance into the dermal layer of the skin, & hence the bloodstream, for essential oils.
• Glands
The Sebaceous glands
The sebaceous glands are attached to the hair follicles and produce an oil called sebum
which is secreted onto the surface of the skin. Sebum lubricates the hair follicle and hair
shaft, and acts as an emollient/lubricant for the skin, protecting it from moisture loss. It also
acts as an anti-bacterial agent. Some researchers believe that sebum’s primary function may
be as a pheromone, a hormone whose scent attracts the opposite sex. Sebaceous glands are
most concentrated on the face, scalp, neck, and upper back and chest. The acid mantle, which
protects the surface of the skin, is made up of perspiration and sebum.
Sebaceous Lipids
Although the majority of lipids produced by all other organs of the human body are alike, the
sebaceous gland produces some unique species that cannot be found in any other organ of the
body.20 The main components found in sebaceous lipids include: sapienic acid21, squalene,
wax esters and triacylglycerols (also called triglycerides) and smaller amounts of cholesterol,
cholesterol esters and diglycerides. 22 These components play an important role in supporting
the skins barrier functions as well as insulate and protect underlying organs.
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The predominant fatty acid of sebum is sapienic acid. Sapienic acid is formed in the sebaceous
glands and has powerful antibacterial properties. It is unique to the skin and is not found
anywhere else in the body.
Triacylglycerols are abundant not only in the skin and body but also in vegetable oils such as
olive, sunflower and palm. Wax esters can be found in jojoba oil. Squalene is a triterpene
hydrocarbon and is a natural and vital part of the synthesis of cholesterol, steroid hormones,
and vitamin D in the human body and skin. Olive oil, sunflower oil and wheatgerm oil are
rich in squalene.
Overview of Lipid composition of Sebum and the Epidermis
Lipid composition of various parts of adult human skin
Component
Sebum
Epidermis
Squalene
10 - 14%
<0.5%
Sterol esters
< 1%
10%
Sterols (unesterfied)
0
20%
Free fatty acids
5 - 40%
10%
Wax esters
23 - 29%
0
Triacylglycerols (triglycerides)
41 - 60%
10%
Di- and monoacyl glycerols
1-2%
10%
Glyco- and phospholipids
0
30%
Unidentified
5%
10%
This chart was adapted from Nicolaides, N. 1974
The Sudoriferous glands
The sudoriferous glands, also known as the sweat glands, help to maintain body temperature
by secreting perspiration. The hypothalamus is the key regulator of body temperature and
responds to the temperature of circulating blood. The evaporation of perspiration from the
skin’s surface cools the body. Sympathetic nerves in response to raised body temperature
stimulate sweat glands. There are two types of sudoriferous glands: the apocrine (the larger)
and eccrine (the smaller), each having slightly different functions.
• Eccrine glands are found all over the skin but are particularly abundant on the palms of the
hands and the soles of the feet. The primary functions of eccrine glands include: cools skin,
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excretes water and electrolytes, and flushes microorganisms and harmful chemicals from
the skin.
The sweat glands are controlled by sympathetic cholinergic nerves which are controlled by
a center in the hypothalamus. As such, eccrine glands respond to both temperature and
emotional conditions. Eccrine sweat contains approximately 99% water and 1% solids. The
solids are half inorganic salt (mostly sodium chloride) and organic compounds (amino
acids, urea and peptides).
• Apocrine glands become active at puberty and are present in the axillae (armpits), genital
region and around nipples. Unlike eccrine glands which secrete sweat made up mostly of
water, salt, and very minute amounts of fatty materials, apocrine sweat glands produce
sweat that mostly contains fatty materials.
Apocrine gland activity is the main cause of sweat odor, due to the bacteria that break down
the organic compounds in the sweat from these glands. Emotional stress increases the
production of sweat from the apocrine glands, or more precisely: the sweat already present
in the tubule is squeezed out. Apocrine sweat glands essentially serve as scent glands.23
• Sensory nerves
The skin is one of the main sensory organs of the body and contains large numbers of nerve
endings. Krause’s end bulbs are round nerve endings that register cold. Ruffini’s’ corpuscles
are tubular-shaped nerve endings that register heat. Meissner’s corpuscles are oval-shaped
and register the sensation of light touch. The Pacinian corpuscles are the largest nerve
endings and register deep pressure and vibration. Pain is registered through the skin through
many free nerve endings.
Certain areas of the body, such as the palms, soles, lips, and external genitalia, have a greater
concentration of sensory receptors and are therefore more sensitive to touch. 24
• Nails
Nails on the fingers and toes serve to protect, and in the case of fingernails, aid in grasping
and picking up small objects. The nail itself is made of keratin, the same material hair is
composed of. Nails have no nerve endings. Fingernails help humans to scratch things, peel
fruit, open things, pick away the outer layers of other edibles, undo knots, and perform a
variety of other tasks. 25
Nails also give clues about many internal conditions and skin problems and therefore can be
used as diagnostic tools. The following chart outlines clues the nails can provide.
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Clues the nails provide
Abnormality
Appearance
Internal Condition
Beau’s lines
Horizontal grooves
correspond to periods of severe
illness
Pale nails
Color is pale to very pale white
Sometimes be a sign of serious
illness, such as:
•
•
•
•
Anemia
Congestive heart failure
Liver disease
Malnutrition
Splinter hemorrhages
Small dark brown or rust flecks
Anemia
Red lunula
Red discoloration in front of the
cuticle
Congestive heart failure
Clubbing
Curving of the nail with thickening of
the fingertip
Liver disease
Spoon nails
Inward curving of the nails to
resemble a spoon
Malnutrition
Double white lines
Transverse white lines that move out
as the nail grows, they occur in pairs
Liver disease, malnutrition
Yellow nails
the nail is yellow and there may be
thickening in the nail bed or the nail
may be raised
Fungal infection
Rippled nails
Rippling or pitted
Early sign of psoriasis or
inflammatory arthritis
Cracked or split nails
cracked and split
Dry, brittle nails that frequently
crack or split have been linked to
thyroid disease. Cracking or
splitting combined with a yellowish
hue is more likely due to a fungal
infection.
This chart is derived from: Leffell, 2000 and http://www.medicinenet.com/
nail_health_pictures_slideshow/article.htm
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Taking care of the nails
Along with a healthy diet and nutritional supplements/vitamins, vegetable/seed oils
such as sesame oil can be very beneficial for the nails. I have noticed that the more I
have integrated sesame oil into my daily life as a skincare oil the healthier and
stronger my nails have become.
The Hypodermis or Subcutanea
Below the dermis is the third layer of the skin, called the hypodermis or subcutaneous layer.
Connective tissue fibers connect the hypodermis to the reticular layer of dermis. It varies in
thickness and is made up of clumps of fat-filled cells, called adipose cells, that give the body
smoothness and contour, and elastic areolar (areolar tissue is loose connective tissue that
consists of a meshwork of collagen, elastic tissue, and reticular fibers - with many connective
tissue cells in between the meshwork of fibers).
Tidbit fact: The hypodermis is the site of subcutaneous injections using hypodermic
needles.
The hypodermis layer serves as: a stabilizer for the skin, a shock absorber and cushion for the
vital organs, a storage area for energy, and an effective insulator. It also houses a network of
arteries that form capillaries that branch into the dermis layer. The subcutanea fat lies on the
muscles and bones, to which the whole skin structure is loosely attached by connective tissue.
The Subcutanea and Cellulite of the thighs
The subcutanea of the thighs have three layers of fat, with two planes of connective
tissue (ground substance) between them. The basic construction of these layers differs
between male and female. In women, the fatty tissue is composed of large ‘standing
fat-cell chambers’, which are separated by radial and arching dividing walls of
connective tissue anchored to the overlying connective tissue of the skin (corium). In
men, however, the uppermost part of the subcutaneous tissue is thinner and has a
network of criss-crossing connective tissue walls. Also, the corium, or tissue between
the subcutaneous and dermal layers, is actually thicker in men than women.
It is due to this different structure in fatty tissue which makes women more prone to
cellulite in the thigh area. In women, the corium becomes progressively thinner and
looser which allows fat cells to migrate into the dermal layer of the skin. At the same
time, the connective tissue is also breaking down or thinning which is the main
instigator in the development of cellulite and is responsible for the ‘mattress
phenomenon’.
(Extracted from: Pizzorno, J.E. & Murray, T. (1999). Textbook of Natural Medicine. London, England:
Churchill Livingstone., pg. 1161-1162)
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- 22 © The East-West School for Herbal and Aromatic Studies and Jade Shutes
Essential oils as novel skin penetration enhancers
There is increasing interest in essential oils as novel dermal penetration enhancers by the
pharmaceutical industry. Transdermal drug delivery is defined as the controlled release of
drugs through intact and/or altered skin to obtain therapeutic levels of a drug systematically
and to affect specified targets for the purpose of, for example, blood pressure control, pain
management, and others. The advantages of transdermal drug delivery include: bypassing
gastrointestinal incompatibility and hepatic ‘first pass’ effect; reduction of side effects due to
the optimization of the blood concentration-time profile; predictable and extended duration of
activity; patient-activated/patient modulated delivery; elimination of multiple dosing
schedules, thus enhancing patient compliance; and reversibility of drug delivery by removal
of drug source.26
Currently the worldwide market revenues for transdermal products are US$3 billion with an
annual projected growth of 12%. Transdermal delivery systems are currently available for
motion sickness, cardiovascular disease, smoking cessation, hormone replacement therapy,
and pain relief (for chronic pain). Transdermal products for cardiovascular disease,
Parkinson’s disease, Alzheimer’s disease, depression, anxiety, attention deficit hyperactivity
disorder (ADHD), skin cancer, female sexual dysfunction, post-menopausal bone loss, and
urinary incontinence are all at various stages of formulation and clinical development.27
Drug molecules in contact with the skin surface can penetrate by three potential pathways:
through the sweat ducts, via the hair follicles and sebaceous glands (collectively called the
shunt or appendageal route), or directly across the stratum corneum.28 The majority of skin
penetration enhancement techniques are currently being focused on increasing the transport
of drugs across the stratum corneum rather than through the appendages. The lipid-proteinpartitioning theory, as developed by Barry and coworkers (1989-1991) describe the
mechanisms by which enhancers effect skin permeability. These mechanisms include:
disruption of the intercellular bilayer lipid structure, interaction with the intracellular proteins
of the stratum corneum, and improvement of partitioning of a drug, coenhancer, or cosolvent
into the stratum corneum.
According to several research studies, essential oils, in particular terpenes, increase
diffusivity of drugs within the stratum corneum by disrupting the intercellular lipid barrier
and by opening new polar pathways within and across the stratum corneum. Essential oil
constituents that have been found to increase dermal penetration of drugs include:
Hydrocarbons: d-limonene, alpha-pinene, beta-carene; Alcohols: alphaterpineol, terpinen-4ol and carvol; Ketones: carvone, pulegone, piperitone, and menthone; Oxides: 1,8 cineole;
and essential oils of ylang ylang, anise, and eucalyptus. Alcohols, ketones and cyclic ethers
were most effective accelerants of 5-fluorouracil (a drug used in the treatment of cancer)
permeation. 29
I have included this information not so much because it is directly relevant to the application
of aromatherapy by the average aromatherapists, but rather to gain insights into the depth of
potential applications for essential oils. In relation to essential oils and the skin, research
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- 23 © The East-West School for Herbal and Aromatic Studies and Jade Shutes
studies have shown that the application of German chamomile essential oil in a gel base
increases transdermal permeation and absorption of water, thereby increasing hydration in the
skin.30
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Resources for learning more
Intro to Fatty Acids and Triglycerides
http://rdfeinman.wordpress.com/2011/10/20/intro-to-fatty-acids-and-triglycerides/
Other References
Howard, D. Dry Skin - It’s a sure thing. Les Nouvelles Esthetiques, May 2005.
Leffell, D. (2000). Nails. Retrieved on May 15, 2012 from: dermatology.yale.edu/.../Chapter
%2015%20Nails_tcm101-36904.pd...
Pugliese, Peter T. Physiology of the Skin. Carol Stream, IL: Allured Publishing Corp., 1996.
REFERENCES
1
Van De Graaff, K M and Fox S I. (1995). Human Anatomy and Physiology. Wm. C. Brown Publishers.
2
Juhan, D. (1987). Job’s Body. New York: Station Hill Press.
3
IBID.
4
Pugliese, Peter T. Physiology of the Skin. Carol Stream, IL: Allured Publishing Corp., 1996.
5
Kusmirek, J. (2002). Liquid Sunshine. Glastonbury, England: Foramicus.
6
Funnel, R. (nd). What is a dendritic cell?. Retrieved October 2, 2005 from: http://cmmg.biosci.wayne.edu/asg/
dendritic.html
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Voegeli D. (2007). The role of emollients in the care of patients with dry skin. Nursing Standard, 22,7, 62-68.
8
Wertz, P. (2000). Lipids and barrier function of the skin. Acta Derm Venereol; Supp 208: 7-11.
9
Bensouilah, J. and Buck, P. (2006). Aromadermatology. Abingdon, U.K.: Radcliffe Publishing Company.
10
Wertz, P. (2000). Lipids and barrier function of the skin. Acta Derm Venereol; Supp 208: 7-11.
11
Essential Fatty Acids and Skin Health. Retrieved on June 5, 2012 from: http://lpi.oregonstate.edu/infocenter/
skin/EFA/index.html
12
Wertz, P and Downing D T. (1990) Metabolism of linoleic acid in porcine epidermis. Journal of Lipid
Research Volume 31, 1990, 1839-1844.
13
De Haven C. (2007) Dry Skin. Science of Skincare, LLC.
14
Truchetet E, Brandle I, and Grosshhans E. (1988). Skin changes, pathophysiology and therapy in deficiency
of essential fatty acids. Z Hautkr 63: 290-301.
15
Tharp M, Leffell D, Orlow S, and Waldorf H A. (2006) The Importance of maintaining hydration for skin
barrier health. Skin and Allergy News. Supplement.
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Revis DR, Seagle MB. Skin anatomy [online]. E-medicine; 2006 [cited 7 March 2006]. Available from URL:
http://www.emedicine.com/plastic/topic389.htm
17
Pugliese, Peter T. Physiology of the Skin. Carol Stream, IL: Allured Publishing Corp., 1996.
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- 25 © The East-West School for Herbal and Aromatic Studies and Jade Shutes
18
Juhan, D. (1987). Job’s Body. New York: Station Hill Press.
19
Ikomi F and Schmid-Schonbein G W. (1995). Lymph transport in the skin. Elsevier Science.
20
Pappas, A. (2009). Epidermal surface lipids. Dermato-Endocrinology, Vol 1:2
21
IBID.
22
Pappas, A. (2009). Epidermal surface lipids. Dermato-Endocrinology, Vol 1:2
23
(http://en.wikibooks.org/wiki/Human_Physiology/Integumentary_System#Eccrine_.28a.k.a._merocrine.29
24
Van De Graaff, K M and Fox S I. (1995). Human Anatomy and Physiology. Wm. C. Brown Publishers.
25
http://www.wisegeek.com/why-do-we-have-fingernails-and-toenails.htm
26
Thong, H.Y., Zhai, H., and Maibach, H.I. Percutaneous Penetration Enhancers: An Overview. Skin Pharmacol
Physiol 2007;20:272-282.
27
Benson, H.A.E. Transdermal Drug Delivery: Penetration Enhancement Techniques. Current Drug Delivery,
2005,2,23-33.
28
Benson, H.A.E. Transdermal Drug Delivery: Penetration Enhancement Techniques. Current Drug Delivery,
2005,2,23-33.
29
Thong, H.Y., Zhai, H., and Maibach, H.I. Percutaneous Penetration Enhancers: An Overview. Skin Pharmacol
Physiol 2007;20:272-282.
30
Harris, B. (2006). Dermatology and wound care: excerpts from the Essential Oil Research Database.
International Journal of Clinical Aromatherapy, Vol 3:1, 2.
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