Eczema is a term that is used for a group of skin conditions that have a similar pattern of changes within the skin. The word eczema is derived from the Greek and means "to boil or flow out". Eczema is a common skin condition which can affect anyone at any age. Another word for eczema is dermatitis which comes from derma, meaning skin, and itis, meaning inflammation. Skin inflammation is the main feature of eczema. The inflammation leads to formation of tiny blisters (vesicles) in the skin, which soon burst or are scratched open, which, leads to the weeping and the "flowing out" of fluid. This inflammation is caused by chemicals and cells in the body's immune system. The chemicals and the cells react within the skin in a complex way to cause inflammation and skin damage.

There are not always vesicles present, but even if none are visible, the skin, when examined under a microscope reveals fluid between the cells of the skin. This fluid pushes the cells apart and results in an appearance that is described as spongiosis, because the tissue of the skin under a microscope looks like a sponge. All varieties of eczema will show this spongiosis along with some inflammation around the superficial blood vessels. These blood vessels are dilated which results in the hot, red inflamed feeling and appearance. The inflammation in the skin irritates nerve endings which leads to the itchiness of eczema.

The appearance of eczema

The appearance of the skin is changed by eczema. If the condition is mild then the skin may simply look slightly scaly and pink. If the inflammation is greater then the skin becomes bumpy and red and then may blister or weep a clear serous fluid. In those with dark skin, the patches of eczema may appear dark rather than red. Sometimes there may be scabs, pus-filled spots or yellow crusts on the skin, especially if the skin has become infected. In eczema which is chronic (long-standing) the skin may become thickened, leathery and cracked, in particular around joints and on the hands and feet. Repeated scratching combined with inflammation can lead to pale or darkened patches on the skin. These slowly return to normal when the condition is controlled. These changes in skin colour take place in all skin types, but the darker the skin is to begin with the more obvious they appear.

The exact nature and combination of changes in the skin with eczema varies considerably between individuals. This means that no two people will find that their eczema looks the same. Even though eczema can look extremely unpleasant, it is important to note that it is not contagious. You cannot catch it from someone who is affected or pass it on.

Different types of eczema

There is no simple way of classifying eczema. There are numerous triggers and causes of eczema. Some are external, such as irritants, allergy and bacterial infection. Some come from within the body. The types that come from inside the body are called "intrinsic" and include "atopy"(having a genetic tendency to eczema, asthma and hay fever), reactions to stressful circumstances and raised venous pressure in lower leg veins. These triggers and causes are not mutually exclusive, so more than one may be a factor in one individual person. It is usually possible, though, to give a general label to the primary underling causative factor.

It is useful as well to classify conditions in terms of how long they have been present. In medicine the term "acute" refers to a condition that suggests a rapid onset and a short duration. Whereas "chronic" means continuing for a long time. The time course may also provide clues to the causative trigger or triggers.

Most classifications are not perfect but do help to indicate the different triggers or factors that are involved in causing the same skin changes. One way of classifying eczema is as follows:

Primarily caused by external factors- extrinsic

Allergic.

In this type the body's immune system is reacting or over-reacting to something that has come into contact with the skin or has been taken in via the mouth.

Irritant.

This form is caused by direct irritation of the skin by such factors as chemicals such as detergents in washing products.

Physical factors.

Examples include: friction and chronic rubbing, artificial ultraviolet light and sunlight.

Internal and other causes – intrinsic

Atopic.

This is often associated with asthma, hay fever and food allergies. Pompholyx. This takes the form of lots of tiny very itchy blisters (vesicles) on the hands and feet.

Seborrhoeic.

This type is caused by yeasts that are present on the skin.

Venous.

This type is also known as varicose, stasis or gravitational eczema. This refers to a form that occurs on the lower legs due to problems with venous drainage and increased pressure within the superficial veins of the lower legs, which may be varicose.

Discoid.

This is a descriptive term for a type of eczema that occurs in roundish patches with no obvious cause.

Asteatotic.

This type usually occurs in the elderly and may be caused by excessive washing and dry environments with a low humidity. The skin has an appearance like crazy paving.

Neuro-dermatitis.

This type is often known as lichen simplex, and is caused by chronic excessive scratching or rubbing.

How does eczema damage the skin?

The skin of the human body provides an essential barrier from the outside environment. It is vital in preventing the body from losing too much heat or water and in keeping out bacteria (germs). The skin is made up of an outside layer known as the epidermis and a thicker layer below, called the dermis. Both of these layers contain cells, water, oils and fats.

The softness and smoothness of the skin is dependent on the correct balance of oils, fats and water in the epidermis. Skin that is healthy contains a lot of water. In eczema the skin tends to produce less oils and fats. Without a good "mortar", the cells of the skin tend to dry out and shrink. This drying out leaves gaps in the skin barrier through which further water may be lost. The gaps can also permit bacteria and harmful chemicals from the outside world to penetrate into the skin more easily. These gaps are too small to be seen initially, but as the disease gets worse they become apparent as visible fissures and cracks.

The epidermis is made up of a “brick wall” of keratinocytes (skin cells) that are held together by a cement (the mortar) which mainly consists of fats or lipids. The many different layers begin with living cells that gradually move up to the surface, die and are then shed. This whole process takes about 28 days. The lipid cement enables to brick wall to be an extremely effective barrier against the outside world.

The dermis is the middle layer and consists of strong structural fibres named elastin and collage. These provide the elasticity and strength of the skin. The dermis also contains the blood vessels that provide the oxygen and nutrients to the epidermis and dermis.

The deepest layer of the skin is the subcutis. This is mainly made up of an insulating layer of fat cells.

In eczema is the epidermis and dermis that are affected. The most marked changes are seen in the epidermis. The inflammation leads to leaky blood vessels which cause fluid to build up between the keratinocytes (the bricks) causing them to separate a little. The brick wall assumes a spongy appearance. As the eczema becomes long standing (chronic) the repeated rubbing makes the epidermis regenerate more rapidly and the epidermis becomes thickened.

Finally the condition causes the upper layer of the dermis to become flooded with white blood cells. These are part of the body’s immune system or defence against infection. The white blood cells leak out of the blood vessels and may even spread up into the epidermal layer. Medical research suggests that it is these white cells that drive the entire process of inflammation.

Is eczema the same as dermatitis?

In short: yes and no!

“Dermatitis” is a general term that means inflammation of the skin. All eczema is dermatitis, but there are other conditions that can be called dermatitis and that fall within the disease grouping of dermatitis.

Most of the various types of eczema can, and often are, interchangeably called dermatitis. The word dermatitis is more often used in the USA. In the past, more than now, eczema that was caused by an irritant or allergic factor in the workplace was named contact dermatitis, and there were possible compensation issues.

With some forms of eczema the word dermatitis is more commonly used. For example: neuro-dermatitis, photo-dermatitis and napkin (diaper) dermatitis. For other conditions the word eczema is commonly preferred. For example: Asteatotic eczema. For some of the remainder, like discoid and seborrhoeic, the two terms are used interchangeably.

It can therefore be confusing, and if in doubt, it is best to ask your doctor or nurse whether they mean something different from your particular understanding of the words.

Why can the skin weep with eczema?

Skin that is affected by eczema can be extremely dry or it may sometimes weep. If you imagine the epidermal layer to be like a sponge, then it is possible to see the fluid leaking out and making the outer layer stretch up into little blisters. If these break then fluid can leak out, leaving a wet weeping area. When this occurs the skin has lost some of its protective barrier function.

Why is skin affected by eczema so susceptible to irritants?

When fluid collects in the epidermis, the keratinocytes separate and the cement becomes disrupted. This leaves cracks in the barrier and irritants that would normally remain on the surface are able to pass through to the more sensitive dermis. There are some irritants, like soaps and detergents, which are able to dissolve the lipid-based cement, leading to even further breakdown and damage to the protective barrier function of the skin.

Why does eczema itch?

The current understanding of the sensation of itch is still rather poor, so this question is difficult to answer. It is known that there are tiny nerve cells within the skin that transmit “itch” messages to the spinal cord and then to the brain. These same nerve fibres can also transmit pain signals. There are areas in the brain that receive these signals and which then interpret them as being either a pain sensation or an itchy sensation. There are two different types of nerve fibres that are involved. One of these transmits messages more rapidly. This helps to explain why itching can be made up of an initial pricking sensation followed by a diffuse itching or burning sensation.

Why eczema causes itching is not really fully understood. It has been speculated that the dry, inflamed skin of eczema causes these nerve fibres too fire off, producing an itch. There is also some evidence that these nerve fibres and the neurotransmitters (chemicals that transmit messages from nerve to nerve) are altered and abnormal in some way in eczema. Thus, it is possible that the abnormal itching sensation is the initial problem, with the other changes being secondary (possibly as a result of the damage caused by scratching). Specialists have commented that a lot more research needs to be done before there is a clearer picture.

The diagnosis of eczema.

There is no specific test for eczema and the diagnosis is made by doctors on what is known as “clinical grounds”. This involves taking a careful medical history of the problem and any family history of eczema, asthma or hay fever. Examination of the skin, added to the clues from the history allows the diagnosis to be made.

Some individuals with atopic eczema may have blood tests that are abnormal. For example they may have high levels of an antibody called an immunoglobulin E (IgE). Antibodies are chemicals produced within the body that act as a defence against infections but are also involved in allergic reactions. The causes or triggers of allergy (known as allergens) can lead to raised levels of linked IgE, which can be measured in an ELISA blood test. However, these tests do not make a definite diagnosis of atopic eczema, because it is possible to have abnormal results and never develop eczema. In contrast it is possible to have definite eczema and have normal IgE levels.