Definitions

The word ‘eczema’ comes from Greek words that mean ‘to boil over’. ‘Dermatitis’ comes from the Greek word for skin and both terms refer to exactly the same skin condition. For simplicity eczema is the term generally used here, although the two words are interchangeable.

Eczema is an itchy inflammation of the skin associated to a varying degree with other features such as:

• redness of affected areas of skin
• generally dry skin, which is often thickened in the areas that have been scratched
• lumps or blisters in affected areas
• signs of superficial infection such as weeping or crusty deposits.

Eczema is divided into a small number of subgroups based largely on the factors that may be most important in causing eczema in any one individual, but it is important to recognise that the symptoms and appearance of the skin in all these types can be exactly the same. Also, the classification system is far from perfect as it is often difficult or impossible to accurately say what causes eczema to occur in any one person.

The lines of treatment of the different types of eczema are also similar. The main differences are to do with the particular factors causing an individual’s eczema. Thus if it is thought to be mainly due to exposure to an irritant substance at work then removal or protection from this irritant will be an important part of managing that person’s eczema compared to someone else with no such history of exposure.

Main Groups

• Atopic: the ‘allergic’ type often seen in people who also have hay fever or asthma.
• Allergic contact: due to skin contact to a substance to which the individual is sensitive. The same substance does not cause eczema in a person who is not sensitive to it.
• Irritant contact: due to skin contact with irritating chemicals, powders, cleaning agents, etc. Contact with such a substance is likely to cause eczema in any person, although a degree of individual variation still exists.
• Discoid: appears as discrete islands of eczema on a background of normal skin.
• Seborrhoeic: in infants appears in the nappy area and the scalp. In adults, also appears on the scalp and in the skin creases between the nose and sides of the mouth. Can be caused by yeast infection.
• Others: a miscellaneous group including eczema of the legs caused by varicose veins and pompholyx – an intensely itchy form located on the hands and composed of small or (sometimes) large blisters.

Eczema in practice

Eczema is a common condition. Atopic eczema affects about 10-20 per cent of schoolchildren and 3-5 per cent of adults in the UK, and it is getting more common. An increase of between two- and five-fold has been seen over the past 30 years, for reasons that are far from clear. It seems likely though that increasing exposure to allergens (protein substances to which people can become allergic) such as house dust mite and other environmental factors have been the main causes of this increase.

Although some older industrial practices have reduced the level of exposure of workers to irritant chemicals there are still plenty of examples of poor practice, or of inadequate care being taken at the individual level in handling materials known to potentially cause irritant contact eczema. Even within the home environment ever more cleaning agents, solvents, detergents, oils and other materials potentially harmful to skin are easily available.

Eczema treatment is generally effective in most people but severe eczema can be difficult to clear. Good adherence to the basic elements of treatment will usually work well but only rarely can eczema be said to be curable. It is unusual to be able to identify and eliminate a single agent causing the skin reaction and most of the time we have to settle for improving the condition rather than getting rid of it altogether.

Itch

This is the main symptom, and without it a rash is not due to eczema (unless the itch has been improved by treatment). Itch is also a common feature of many other skin conditions as well as being a symptom of a range of diverse medical conditions not primarily to do with the skin, so although it is an ‘essential’ symptom when diagnosing eczema it is not specific for it. We still do not fully understand what causes itch, but nerve fibres specialised in transmitting the itch sensation appear to exist within the skin. Like other nerves, these are ultimately connected to the spinal cord and so to the brain. It used to be thought that the sensation of pain travelled along the same nerve fibres as for itch but this seems now to be unlikely. Interestingly, the two sensations can act against each other. Thus relief from severe itching may sometimes be had from inflicting pain instead, as might be seen in someone who prefers the discomfort of a very hot bath to that of constant itching. The act of scratching may itself cause nerve signals to travel down the pain fibres, blocking the sensation of itch from being experienced.

Redness

Increased redness of the skin usually means increased blood flow. An extensive network of tiny blood vessels (capillaries) is present in the deeper layers of the skin that project loops of smaller vessels into the more superficial layers. The very top layer of skin is composed of dead skin cells and has no blood supply, so a superficial cut to this level will not bleed. When skin is inflamed the local network of blood vessels widens, increasing the flow of blood and making it red. The process of inflammation in eczema is complex and can be triggered by a range of factors but an important additional one to take into account when eczemaflares up is the presence of bacterial infection. When bacterial infection gets into the deeper layers of the skin there is usually a marked increase in redness and heat from the tissues. Recognising that this may be due to infection is important in bringing the eczema under control.

Thickening

The skin of areas of eczemathat have been inflamed for a while are usually much thicker than unaffected skin. Mainly this occurs as a protective response of the skin to the repeated trauma of scratching. Eczema often affects the skin in areas around joints such as the elbow, behind the knees and in front of the ankles (the ‘flexures’) where the skin also needs to be particularly flexible. Commonly one will see splits in the skin here (fissures), as the thickened skin is unable to bend as it would normally.

Blisters

The microscopic study of skin structure in eczema shows there is less adhesion between the skin cells, particularly in the upper layers of the skin. This contributes to scaling and makes it easier for skin bacteria to get into the deeper layers, between the gaps. It also makes it possible for tissue fluids to ooze between the cells and, if sufficient, to gather into collections or blisters. Small blisters may be seen in active eczema but occasionally large ones may occur, either due to the particular nature of the eczema or because of skin infection coming along as well when the blisters may be filled not only with clear fluid but also pus.

Crusts

The fluid that oozes from inflamed skin is rich in protein. When this dries out in contact with air the protein is left behind as a crusty deposit. Often this occurs in conjunction with infection, when the infected crusts typically have a golden colour. A similar crusting is seen in the infectious skin condition called impetigo, which is commonly seen in children of primary school age as it is easily passed on by touching. In impetigo treating the infection eliminates the problem, but it is of course only part of what’s required in eczema. Often doctors refer to infected eczema as being ‘impetiginised’.