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How does the skin work?

Your skin is your body’s largest organ. The skin of an average adult comprises one to two square metres and weighs between three and four kilograms.

Your skin’s main function is to act as a protective barrier between your body and the outside environment.

ECZEMA is a condition that specifically targets the skin. Your skin is a living and vital organ. It is not a simple external layer that you can keep in good condition by occasionally applying body wash or cream. It is very complex and is affected by various other systems operating in your body, including the immune, hormone and digestive system. Problems manifesting on the surface of the skin may therefore signal imbalances and malfunctioning of one or more of the body’s systems.

THE SKIN’S BARRIER FUNCTION

Our skin forms a waterproof cover for our bodies. Beneath it there are bones, muscles, ligaments, nerves and internal organs, all of which are highly susceptible to infection from foreign microbes. Your skin thus acts as a barrier between these internal building blocks of your body and the external environment.

The skin also has several other functions:

•It acts as a sensory organ. A network of nerve cells in the skin enables us to feel cold, heat, touch and pain. If these nerve cells are damaged, the result is neuropathy, which means that our sensory capability – to experience pain, for instance – is lost in the damaged section.

•The skin controls our body temperature.

•It plays an indispensable role in the absorption of vitamin D from sunlight. At the same time, it blocks the penetration of harmful ultraviolet rays of the sun.

What happens in an eczematous skin?

Author Sue Armstrong-Brown explains the appearance of an eczematous skin in a simple way:

‘The skin develops little fluid-filled vesicles, like bubbles, which weaken its structure. Blood vessels in the lower layers of the skin (the dermis) swell, and blood cells that fight infection migrate into the skin, causing redness and itch.

‘Normal cell growth in the epidermis (outer skin layer) speeds up, causing cells to pile up and thicken the skin. The cells are smaller and weaker than healthy skin cells and the lubricating liquid between the cells, which helps to make normal skin flexible and waterproof, is disrupted.

‘Older cells build up on the skin’s surface, because the biological “glue” that holds them together stops breaking down and allowing the cells to be gradually shed. This results in the thick layer of dead dry skin at the top of the epidermis.’

(The Eczema Solution, pp. 13–14)

The most important function of the skin, however, is to act as a barrier against onslaught from the environment. Day and night, your skin is at work to protect your body. How does it do that?

It retains moisture inside the body and prevents excessive moisture loss. Unrestrained loss of body fluids would mean that our bodies, from our water-rich internal organs to the tiniest cells, would shrivel up and we would die.

Our skin further protects us from assaults from the outside environment, such as knocks and blows, temperature changes, the rays of the sun, poisonous substances, and chemicals and pathogens that may penetrate the skin and cause disease and infection.

If the skin is damaged – through continuous scratching, for instance – all its functions are affected. It then loses its ability to retain moisture inside the body, dries out and becomes less supple and elastic. An overly dry skin is particularly vulnerable to eczema flare-ups.

Why do we focus so extensively on the skin’s barrier or protective function? Because eczema is caused by a defect in the barrier function. This defect can in turn be ascribed to problems with the immune system. Eczema itself can lead to overstimulation of the immune system, thus damaging the barrier function even further.

A pathogen is any micro-organism, such as a bacterium or a virus, that can cause a disease.

THE LAYERS OF THE SKIN

We are better able to appreciate the nature and causes of eczema if we understand the structure of the skin.

Human skin consists of three layers (see Figure 3.1):

•Hypodermis. The bottom layer is the hypodermis, or subcutaneous tissue.

•Dermis. The hypodermis is followed by a living middle layer known as the dermis.

•Epidermis. The thin, strong, protective outer layer is called the epidermis.

The hypodermis or subcutaneous tissue

The hypodermis is a fatty layer deep in the skin that insulates the body against heat and cold and acts as a protective padding or shock absorber. The thickest part of the shock absorber is found on the buttocks, the palms of the hands and under the soles of the feet. Nutrients and energy are stored in the hypodermis, enabling a person to survive without food for a long period.

As we grow older, the hypodermis starts to shrivel and this leads to the thinning of the skin in old age.

Although the hypodermis fulfils important functions, it does not play a crucial role in the development of eczema. It does, however, remain important for your skin’s general health.

The dermis

The dermis forms the largest part of the skin. It provides the skin with essential nutrients, as well as a strong structure.

Collagen and elastin, containing a large amount of water, are two important structural proteins found in the dermal layer. Cosmetic houses often emphasise the importance of collagen in counteracting the skin’s ageing process. We also know that the loss of too much fluid from the skin results in the dryness and itchiness typical of eczema. The network of collagen and elastin fibres in the skin therefore has an important function. Collagen strengthens the skin and elastin keeps it flexible so that you can bend, stretch and move around without damaging your skin.

Eczema is often found on the hands. A contributing factor is that only a small amount of sebum is secreted on the hands, causing very dry skin in that area.

The dermis also contains the sweat glands, which control your body temperature, as well as blood vessels, nerves and hair follicles.

Sebaceous glands, which play an important role in eczema, are also found in the dermis. These glands secrete a sebum, or biofilm, that gives a healthy glow to normal skin. The sebum is your own, natural antibacterial oil that keeps your skin soft and moist and protects it against harmful environmental factors. The overproduction of sebum may cause acne, while underproduction leads to dryness and may cause eczema.

Sebum production is directly controlled by a complex hormone system and the hormonal signals are dependent on an even more complex balance of elements that include genetics, environmental conditions, metabolic conditions, stress and diet.1 It follows that eczema in itself does not have a simple cause or solution.

The dermis provides a supporting structure to the epidermis. It sends messages, nutrients and fluids to the epidermis to help it protect the body against the environment and react against adverse activities within the body.

If eczematous skin is broken through scratching, the dermal layer becomes vulnerable and infection may develop.

The word ‘epidermis’ is derived from two Greek words: epi, meaning ‘on top of’ and derma, meaning ‘skin’.

The epidermis

The outer layer of skin is known as the epidermis. Skin cells are produced deeper inside the skin, close to the dermis. New cells are constantly being produced and, as they increase in numbers, older cells are systematically being removed to the skin surface or epidermis. There they grow to maturity, dry out and flatten and are eventually shed. This process takes about a month to complete in young people and twice as long in older people.2

Lipids, found in skin cells, are molecules that contain fat and wax, which keep the skin smooth and moist.

Keratin is a horny protein also found in human nails and hair.

The three layers of the skin can be compared to a plant. The hypodermis is the root, the dermis the stem, and the epidermis the leaves and flowers that display the beauty of the plant.

Healthy, beautiful leaves and flowers need a healthy root system that can absorb nutrients from the earth. The nutrients need a healthy network of pathways in the stem to carry them to the leaves and flowers. If the roots and the stem (the hypodermis and dermis) are in good condition, the flowers and leaves (the epidermis) will be lush and healthy.

‘The word “slowly” truly describes the healing process of eczema. My healing took a little over six months. There isn’t any magical, secret overnight fix.’

– Harrison Li

The epidermis – this waterproof surface layer of the skin – also has different layers. The outermost part is known as the corneum stratum, or horny layer. This strong, waxy layer develops when skin cells dry out and lipids are released. They form a kind of glue, or cement, that holds the dead cells together. In the dry, dead cells is a protein called keratin that gives the skin its extraordinary strength.

One can compare the corneum stratum to a wall of bricks and cement. Dry cells constitute the bricks and lipids or fats the cement. The dry, dead skin cells, called corneocytes, flatten out and form layers that resemble bricks in a wall. A matrix of lipids between the ‘bricks’ functions as the ‘cement’ that holds the bricks together (see Figure 3.2).

The proteins and lipids in skin cells are indispensable to the all-important barrier function of the skin, but the skin of eczema sufferers does not contain enough lipids to bind the ‘bricks’, or cells, together. Moisture is lost and the result is roughness, dullness and a dry corneum stratum that exhibits cracks and scales. A lot of moisture is consequently lost through the cracks, and the dry skin cells multiply and become a breeding spot for germs.

Simply put, the main focus of eczema treatment is therefore to repair the cement between the bricks to prevent extensive moisture loss, as well as to prevent irritating substances from entering the skin.

The epidermis also contains the important Langerhans cells, which form part of the skin’s immune system. These cells are your skin’s police officers, who track down foreign, harmful organisms and develop antibodies to fight the ‘criminals’. Your immune system is thus activated in order to protect your body against infection. Unfortunately, the eczema sufferer has an overactive immune system that releases too much histamine and thus worsens the eczema flare-up. We explain this in more detail in Chapter 4.

In eczema sufferers, the epidermis is the area where the disease plays itself out. As Dr Adnan Nasir puts it: ‘The epidermis is eczema’s battleground.’3 If there is an eczema flare-up, it is the epidermis that itches, shows signs of infection and appears rough and dry. The causes of this skin condition cannot, however, only be found on the surface of the skin.