Over the millennia, indigenous cultures the world over have utilised plants in multitudinous ways: food, shelter, clothing, medicine, and ceremonial purposes are but some of the many ways that plants have come to be used. Their life-giving properties have been honoured and revered and, even today, the majority of the world�s population uses traditional botanical medicine as their primary form of healthcare. When one considers the diversity of applications that plants provide for, it is easy to understand their increasing importance and usefulness in any healthy lifestyle.

Over the last few decades, the medicinal and cosmetic virtues of plants have become more widely appreciated and utilised in the �developed� world as well. Their many active principles are buffered within a vast complex of constituents that synergistically compose the entire plant. This important feature diminishes the likelihood of adverse reactions to a single component and, because of their inherent harmony with our own biological processes, plant extracts are easily recognised by the body�s established metabolic pathways, ensuring maximal bioavailability without additional stress on the body.

ESSENTIAL OILS

Amongst the thousands of individual constituents contained within each plant are its essential oils, volatile byproducts of cellular metabolism. Essential oils are composed of a complex mixture of principles and are produced and stored within the plant in specialized cells: glands, glandular hair, glandular scales, oil cells, hair cells, oil and resin ducts, and oil containers. They play an important role within the plant (e.g., attraction for pollination purposes; protection from predators or infections) and also provide for many therapeutic applications, both medicinally and cosmetically. Their unique chemical structures lend themselves to transdermal applications exceptionally well, crossing the protective lipid of the epidermis to affect local sites as well as being absorbed into the circulation for systemic distribution.

THE SKIN

A healthy, intact skin barrier provides us protection from the environment (chemical and physical elements) and is our first line of defense against invading micro-organisms. It is our largest organ (surface area approx. 1.5 m2) and is made up of a surface epithelial layer (the epidermis and dermis) and an underlying connective tissue network called the hypodermis (or subcutaneous connective tissue layer) that stores adipose tissue and provides support and flexibility.

The skin�s main functions include:

• Thermoregulation

• Protection

• Metabolic functions

• Sensation: touch, pressure, heat, cold
   

A. EPITHELIUM

The epithelial layer is made up of two regions:

 Epidermis
 Dermis


1. EPIDERMIS

The epidermis is the most superficial layer of the skin and provides the first barrier of protection from invasion of foreign substances into the body. It does not contain any blood vessels, though it does contain nerves and outlets for glandular secretions (sebum, sweat.) The deeper layers of living cells in the epidermis receive their nutrition from blood vessels located in the underlying dermis.

The epidermis is composed of five layers:

 stratum corneum
 stratum lucidum
 stratum granulosum
 stratum spinosum
 stratum germinativum


1. Stratum corneum:

• most superficial skin layer

• provides barrier against the external environment

• lipid layer of stratum corneum is responsible for barrier impermeability towards most substances; also utilised for enhancing transdermal permeability of skin

• comprised of tightly packed, scale-like cells (keratinocytes) that have developed a thickened keratin (protein) layer

• keratinocytes migrate towards the surface and are constantly being sloughed off in a process called desquamation

2. Stratum lucidum:

• between stratum corneum and stratum granulosum

• contains degenerating cells which have lost their nucleus

• cells here are losing water and producing increased amounts of keratin as they move towards the stratum corneum

3. Stratum granulosum:

• formed by many layers of living cells

• contains pigments that determine skin colour

• fits tightly on dermis

• new cells always forming and moving outwards towards the stratum lucidum

• takes at least one month for the cells to reach the surface and be exfoliated

4. Stratum spinosum

• consists of cells joined by prickle-like threads

5. Stratum germinativum

• Single layer of cells responsible for the production and growth of the epidermis

• Melanin produced here (protects the cells below this layer from UV rays)

2. DERMIS

The dermis lays beneath the epidermis and is composed of two layers:

 Papillary Layer
 Deep Layer
 

1. Papillary Layer:

• Contains concentric zones of protrusions called papillae, visible as �fingerprints�

• 2 types of Papillae:
  
  � Vascular � contain a central lymphatic vessel surrounded by capillary vessels
  � Nervous � contain tactile, sensory nervous tissue as well as vessels

2. Deep Layer:

• Comprises 2/3 of the dermis

• Contains few cells but many elastin fibres that give skin elasticity and resilience
   

B. SUBCUTANEOUS LAYER

The subcutaneous layer is made up of three regions:

 Panniculus adiposus
 Connective membrane
 Subdermal connective tissue

1. Panniculus adiposus

• Comprised of adipose (fat) tissue which is distributed over almost entire body surface

• Thickness of 1 to 4 cm. (increased on obese person)

• Provides protection, thermoregulation and energy reserves

2. Connective membrane

• Thickened membrane that supports the adipose layer and forms a barrier between it and the underlying tissues.

3. Subdermal connective tissue

• Present in all areas that the connective membrane is not adhering to subcutaneous structures.
   

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