What is Atopic Eczema / Dermatitis?

It is worth pointing out that the words eczema and dermatitis are for all intents and purposes the same thing.

A strict modern definition of atopic eczema would look like this: A chronic, itchy, superficial inflammation of the skin, frequently associated with a personal or family history of allergic disorders (eg., hayfever, asthma).

Some big words there, but it does not really tell you what is going on! The root of the condition is in the blood, and more specifically, in the immune system. To simplify, imagine you are allergic to a given substance and that the allergen gets into your body or your blood. The first thing that happens is that a specialised cell from the immune system called an antigen presenting cell grabs hold of it. The antigen presenting cells are all over the body and lie in wait for all the bugs and allergens etc. that may invade the body. These cells then take the allergen to other cells of the immune system called the B-cells. The B-cells are the cells that make antibodies. In this instance they make an antibody called IgE. This IgE antibody is then picked up by and bound to another type of cell in the immune system called a mast cell. This is when the problems really start!

The mast cells are normally found in the tissues of the body such as the skin etc., and they contain chemicals including histamine, that when released, set off an immune or inflammatory reaction. Under normal circumstances, such as when a bacteria invades the skin, the chemicals mast cells produce help to neutralise the invaders and attract other immune cells to the area to destroy it. This small immune 'war zone' is best observed when we get a cut or scratch on our skin which is then followed by the typical inflammatory redness and swelling. This process is a normal part of fighting off invaders and also serves as a stimulus to tissue repair after infection or inflammation. It is a controlled process, triggered by an invasion and then reducing slowly when the invaders have been neutralised. The problem for people with allergies is that the 'invaders' are usually normal everyday substances to the rest of us. In allergy sufferers when the IgE binds to their mast cells it sensitises them and the next time the allergen is encountered the immune 'war zones' are triggered off inappropriately and in an uncontrolled fashion all over the place. It is this inappropriate sensitivity or hypersensitivity reaction of the mast cells that then leads to eczema. This is where the family tendency towards allergy comes in. Allergy sufferers appear to have inherited an instability in this otherwise normal immune pathway. It's as though it's balanced on a hair trigger, set off at the slightest provocation.

Atopic eczema is often seen along with asthma, hayfever, urticaria or even anaphylaxis, either in the same patient or in close blood relatives. This is because, quite simply, the same reaction we described above, occurs in these other conditions too, it's just manifesting in a different part of the body.

Atopic eczema can occur at any age, although is very common in infants and children. It is sometimes obviously related to an allergen, milk or wheat for example, but more often than not it is impossible to identify a specific allergen. It can affect any part of the body but classically affects the folds of the elbows and backs of the knees. It can range from one innocuous patch to a wide-spread debilitating condition. There is no predictable course to the condition and it can cause extensive redness, itching and scaling of the skin. In the long-term, itching and constant irritation can lead to hardening and thickening of the affected skin. It may also be 'wet' and ooze clear fluid or it may even become infected.