SKINCARE
Alpha hydroxy acids
Ampoules & serums
Anatomy of the skin
Botox
Chemical peels
Cleansing basics
Cosmetic Surgery
Masks
Moisturisers
Non-surgical facelift
Skin analysis
Skin disorders
Treatment creams
Wrinkle fillers

BODYCARE
Aromatherapy
Massage
Reflexology

OPTIMAL HEALTH
Amino acids
Anti-oxidants
Homeocysteine
High protein diets
Know your fats
Nutrition
Tissue salts
Vitamins & minerals
RDA vs ODI

GENERAL
About me
Articles of interest
Effects of the sun
Fact or fallacy
FAQ's
Newsletter
Products & Prices
To take or not to take
In my humble opinion

THE SKIN

The skin has three layers—the epidermis, dermis, and fat layer (also called the Hypodermis or subcutaneous layer). Each layer performs specific tasks.

EPIDERMIS

The epidermis is the relatively thin, tough, outer layer of the skin. Most of the cells in the epidermis are keratinocytes. They originate from cells in the deepest layer of the epidermis called the basal layer. New keratinocytes slowly migrate up toward the surface of the epidermis. Once the keratinocytes reach the skin surface, they are gradually shed and are replaced by younger cells pushed up from below.

The epidermis is divided into four layers, starting from bottom to top:

The Basal Cell Layer
The basal layer is the innermost layer of the epidermis, and contains small round cells called basal cells. The basal cells continually divide, and new cells constantly push older ones up toward the surface of the skin, where they are eventually shed. The basal cell layer is also known as the stratum germinativum due to the fact that it is constantly germinating (producing) new cells.
The basal cell layer contains cells called melanocytes. Melanocytes produce the skin coloring or pigment known as melanin, which gives skin its tan or brown color and helps protect the deeper layers of the skin from the harmful effects of the sun. Sun exposure causes melanocytes to increase production of melanin in order to protect the skin from damaging ultraviolet rays, producing a suntan. Patches of melanin in the skin cause birthmarks, freckles and age spots. Melanoma develops when melanocytes undergo malignant transformation.

Merkel cells, which are tactile cells of neuroectodermal origin, are also located in the basal layer of the epidermis.

The Squamous Cell Layer - Stratum spinosum
The squamous cell layer is located above the basal layer, and is also known as the stratum spinosum or “spiny layer” due to the fact that the cells are held together with spiny projections. Within this layer are the basal cells that have been pushed upward, however these maturing cells are now called squamous cells, or keratinocytes. Keratinocytes produce keratin, a tough, protective protein that makes up the majority of the structure of the skin, hair, and nails.

The squamous cell layer is the thickest layer of the epidermis, and is involved in the transfer of certain substances in and out of the body. The squamous cell layer also contains cells called Langerhans' cells, which are part of the skin's immune system. Although these cells help detect foreign substances and defend the body against infection, they also play a role in the development of skin allergies.

The Stratum Granulosum & the Stratum Lucidum
The keratinocytes from the squamous layer are then pushed up through two thin epidermal layers called the stratum granulosum and the stratum lucidum. As these cells move further towards the surface of the skin, they get bigger and flatter and adhere together, and then eventually become dehydrated and die. This process results in the cells fusing together into layers of tough, durable material, which continue to migrate up to the surface of the skin.

The Stratum Corneum
The stratum corneum is the outermost layer of the epidermis, and is made up of 10 to 30 thin layers of continually shedding, dead keratinocytes. The stratum corneum is also known as the “horny layer,” because its cells are toughened like an animal’s horn. As the outermost cells age and wear down, they are replaced by new layers of strong, long-wearing cells. The stratum corneum is sloughed off continually as new cells take its place, but this shedding process slows down with age. Complete cell turnover occurs every 28 to 30 days in young adults, while the same process takes 45 to 50 days in elderly adults.
The Stratum Corneum is relatively waterproof and, when undamaged, prevents most bacteria, viruses, and other foreign substances from entering the body.

The epidermis (along with other layers of the skin) also protects the internal organs, muscles, nerves, and blood vessels against trauma. In certain areas of the body that require greater protection (such as the palms of the hands and the soles of the feet), the outer keratin layer of the epidermis (stratum corneum) is much thicker.

THE DERMIS

The dermis is located beneath the epidermis and is the thickest of the three layers of the skin (1.5 to 4 mm thick), making up approximately 90 percent of the thickness of the skin. The main functions of the dermis are to regulate temperature and to supply the epidermis with nutrient-saturated blood. Much of the body’s water supply is stored within the dermis.The dermis layer is made up of two sublayers:

The Papillary Layer
The upper, papillary layer, contains a thin arrangement of collagen fibers. The papillary layer supplies nutrients to select layers of the epidermis and regulates temperature. Both of these functions are accomplished with a thin, extensive vascular system that operates similarly to other vascular systems in the body. Constriction and expansion control the amount of blood that flows through the skin and dictate whether body heat is dispelled when the skin is hot or conserved when it is cold.

The Reticular Layer
The lower, reticular layer, is thicker and made of thick collagen fibers that are arranged in parallel to the surface of the skin. The reticular layer is denser than the papillary dermis, and it strengthens the skin, providing structure and elasticity. It also supports other components of the skin, such as hair follicles, sweat glands, and sebaceous glands.

The dermis contains most of the skins’ specialised cells and structures, including:
Blood Vessels - The blood vessels supply nutrients and oxygen to the skin and take away cell waste and cell products. The blood vessels also transport the vitamin D produced in the skin back to the rest of the body.

Lymph Vessels - The lymph vessels bathe the tissues of the skin with lymph, a milky substance that contains the infection-fighting cells of the immune system. These cells work to destroy any infection or invading organisms as the lymph circulates to the lymph nodes.

Hair follicles - Hair is made of keratin, the same substance that forms nails and the top layer of the epidermis (stratum corneum). Different cells located in the root of the hair make keratin and melanin, which gives hair its color. Humans have two types of hair: vellus (light and fine) and terminal (dark and thick). A sebaceous gland secretes an oily substance called sebum that drains into the canal of a hair follicle to reach the surface of the skin. Together, a hair follicle and its associated sebaceous gland are called a pilosebaceous unit. Hair follicles are distributed everywhere on the body except the palms and soles. In humans, hair is largely decorative, but it also serves a protective function. Eyebrows and eyelashes protect the eyes from dust and sun, while nasal hairs block out foreign bodies from your nose. Scalp hair provides some temperature insulation.

Sweat Glands – The average person has about 3 million sweat glands. Sweat glands are classified according to two types:
Apocrine glands are specialized sweat glands that can be found only in the armpits and pubic region. These glands secrete a milky sweat that encourages the growth of the bacteria responsible for body odour.

Eccrine glands are the true sweat glands. Found over the entire body, these glands regulate body temperature by bringing water via the pores to the surface of the skin, where it evaporates and reduces skin temperature. These glands can produce up to two liters of sweat an hour, however, they secrete mostly water, which doesn’t encourage the growth of odour-producing bacteria.

Sebaceous glands - These glands produce an oily substance called sebum. They are most prominent in the skin of the scalp, face, and upper trunk and are absent from the palms and soles. As part of the pilosebaceous unit, sebaceous glands secrete sebum that drains into the follicular canal and eventually onto the surface of the skin. Sebaceous glands increase in size and produce more sebum in response to increased hormone levels, specifically androgen, during adolescence. They play an important role in the development of acne.

Nerve Endings – The dermis layer also contains pain and touch receptors that transmit sensations of pain, itch, pressure and information regarding temperature to the brain for interpretation. If necessary, shivering (involuntary contraction and relaxation of muscles) is triggered, generating body heat.

Collagen and Elastin - The dermis is held together by a protein called collagen, made by fibroblasts. Fibroblasts are skin cells that give the skin its strength and resilience. Collagen is a tough, insoluble protein found throughout the body in the connective tissues that hold muscles and organs in place. In the skin, collagen supports the epidermis, lending it its durability. Elastin, a similar protein, is the substance that allows the skin to spring back into place when stretched and keeps the skin flexible.

THE FAT LAYER OR SUBCUTANEOUS LAYER

The Subcutis or Hypodermis
The subcutis is the innermost layer of the skin, and consists of a network of fat and collagen cells. The subcutis is also known as the hypodermis or subcutaneous layer, and functions as both an insulator, conserving the body's heat, and as a shock-absorber, protecting the inner organs. It also stores fat as an energy reserve for the body. The blood vessels, nerves, lymph vessels, and hair follicles also cross through this layer. The thickness of the subcutis layer varies throughout the body and from person to person.

The subcutaneous layer lies between the dermis and the underlying fascia covering muscle. This layer is made of groups of adipocytes (fat cells) that are separated by fibrous septa.
It serves three functions: to insulate the body from cold, to absorb trauma and cushion deeper tissues, and to act as storage for the body’s reserve fuel.

SUMMARY
Epidermis: the uppermost layer of skin. This layer contains pigment-producing cells (melanocytes) that give skin its colour. New epidermal cells are produced in the basal cell layer of the epidermis and these cells gradually rise to the outer layer of the epidermis, the stratum corneum, from where the old dead cells are shed.

Dermis: below the epidermis, the dermis contains blood and lymph vessels, nerves, sweat glands and oil glands. The dermis is made up of approximately 95% collagen (for strength) and 3% elastin (for suppleness), which together act as a supportive mattress to the epidermis.

Finally a layer of fatty tissue lies below the skin and gives it structure. This is called the Subcutis or Hypodermis

RELATED ARTICLES
Skin care
Effects of the sun
The peel appeal

Back to top