Eczema is a term used to describe skin which is red, dry, scaly, cracked, blistered, or oozing, or any combination thereof. It is a description, not a diagnosis. Determining the cause of the eczema constitutes a diagnosis and permits rational treatment. There are several common types of disease which may loosely be described as eczema:
- Allergic contact eczema. The classic of this is reaction to poison ivy. If you take a walk in the woods, brush against a plant, and note the appearance of blisters on the skin two days later, the diagnosis of allergic contact reaction to poison ivy is obvious. However, reactions to poison ivy or poison oak may be atypical and may be very subtle.There are many chemicals in our environment which can cause allergic contact dermatitis. Examples would be nickel, fragrances, preservatives, rubber, or latex products. The hallmark of allergic contact dermatitis is that only some people exposed to the allergen will develop a dermatitis. It is not universal. If a rash which appears to be allergic contact eczema appears, a careful history and physical may be all that is required to uncover the culprit; however, in some cases more extensive usage testing or patch testing may be needed.
- Irritant contact dermatitis. Some compounds cause eczema on exposure because they are irritating and/or drying. Examples of these would be harsh soaps, cleansers, or solvents. Unlike allergic contact reactions, which affect only a small proportion of those exposed, a true irritant dermatitis will affect anybody who has adequate exposure to the chemical.
- Atopic dermatitis (A.D.). This is a very common and misunderstood disease. It has been called “the scratch that itches.” Basically, it is an immunologic disease of hyper reactivity of the skin to many exogenous antigens. One of the major antigens which induces A.D. is the bacteria staphylococcus. Therefore, infections of the skin may worsen A.D. It is also a biochemical disease in which the components of the cells are abnormal and fail to hold water. This lack of hydration (dryness) interrupts the normal barrier of the skin and ultimately leads to the appearance of eczema. A.D. is an inherited tendency and is associated with asthma and hay fever. Just as the appearance of the eczema and the exacerbating factors are variable from one person to another, so are the treatment options.
- Dishydrotic eczema. The classical form of this is the sudden appearance of water blisters along the fingers and/or the palms and the soles. These blisters are quite itchy at first and then flatten out and become scaly. This disease tends to be recurrent in individuals who are susceptible. Stress is often an exacerbating factor.
Eczema may also be caused by circulatory problems in the legs (stasis dermatitis), dry air, xerotic eczema, and scalp disease (seborrhea). There may be overlap and coexistence of several types of eczema in the same patient. Diagnosis should be as precise as possible and treatment then tailored to the underlying cause.