Updates on the Eczema and dermatitis

Topical steroid is still the mainstay of treatment, but must be monitored carefully as overuse can further damage the skin barrier and might also lead to rebound inflammation. In patients whose skin is colonized with bacteria such as Staphylococcus, regular use of bleach baths can greatly reduce the frequency of exacerbations. Patients who require excessive amounts of topical steroid might benefit from a course of oral immunosuppressive drug therapy.

Contact dermatitis can affect people without the above mentioned skin barrier defects, but patients with atopic dermatitis often suffer from contact dermatitis as well. Contact dermatitis often occurs after prolonged or repeated skin contact with certain allergens. Plant resins known as urushiols, for example, can cause dermatitis in up to 70% of the population, given enough exposure. These resins are found on the leaves of plants such as poison oak, poison ivy or poison sumac. They are also used as varnish on furniture and lacquer ware. Some people are so sensitive that even contact with molecular amounts of the urushiol allergens can lead to severe outbreak. The most common contact allergen seen in clinical practice is nickel, which is found in a wide variety of household objects such as coins, fasteners, utensils and jewellery, and also in food. Dyes, preservatives, anti-microbials and fragrances found in skin care products are also common culprits. Rubber glove and detergent are common causes of hand dermatitis.

Avoidance is the most important treatment for contact dermatitis. The cause of the dermatitis must therefore be accurately diagnosed so that the patient knows what to avoid. This is usually accomplished by careful history taking, identifying the possible allergens the patient comes in contact with. The diagnosis should be confirmed with patch testing, as contact dermatitis is caused by a cell-mediated rather than IgE-mediated immune mechanism. Avoiding the relevant allergens is usually all that is needed to successfully manage contact dermatitis.

Reference information:  www.allergy.hk , www.hkallergy.org

The information aims to provide educational purpose only. Anyone reading it should consult physician before considering treatment and should not rely on the information above.

Blood tests for specific IgE antibodies

As mentioned in previous articles, allergic reactions can be mediated by different immune mechanisms. The most common type of allergic reaction is mediated by IgE antibodies, and therefore most blood tests for allergy seek to measure allergen-specific IgE. Most of these tests will also measure the total IgE level. There are several obstacles that developers of blood tests must overcome. First, IgE antibodies are mainly found on the surface of mast cells, and the amount of free IgE in the blood is miniscule, and might not truly reflect what is found on the mast cells. Therefore, extremely sensitive methods must be employed to measure these antibodies. These tests employ allergens that are bound to a solid phase to capture IgE antibodies in the blood sample. Anti-IgE antibodies are then used to detect these captured IgE antibodies, and the signal is amplified using enzymatic reactions or radioactivity. This amplification process increases the background noise of the assay, and greatly increases the chance of false positive results.

Second, these assays only measure the binding of IgE to the allergens on the solid phase. While IgE binding is the essential first step during an allergic reaction, it does not necessarily lead to the complete allergic reaction, just as a key that can be inserted into a lock does not guarantee that it can open that lock. Therefore, antibodies that are structurally similar to the antibodies that are being measured will also show up in the assay, but these cross-reacting antibodies might actually be specific for bacterial or other irrelevant antigens. This problem is extremely common in patients with very high total IgE levels, such as patients with eczema who has repeated skin infections. On average, there is a greater than 50% chance of a positive food IgE test result being false. Therefore, the guidelines published recently by the National Institutes of Health in the United States advised against using blood tests to diagnose food allergy. 

Reference information:  www.allergy.hk

The information aims to provide educational purpose only. Anyone reading it should consult physician before considering treatment and should not rely on the information above.

Eczema and dermatitis

Eczema and dermatitis are terms that mean skin inflammation. The two most common types of dermatitis are atopic dermatitis and contact dermatitis. Whereas the two types of dermatitis are indistinguishable pathologically, there are differences in terms of epidemiology, etiology and treatment.

Atopic dermatitis usually starts in infancy or early childhood. The basic problem with atopic dermatitis is an inborn defect in skin barrier function. The skin is an important barrier that protects us from our environment, and normally does not allow allergens to penetrate through. Genetic defects that lead to a reduction in the barrier function allow substances to penetrate the skin more easily. The defects also increase water loss from the skin, and dry skin is a characteristic of this condition. 

Allergens that penetrate through the skin barrier interact with Langerhan cells within the skin, which direct the immune system to develop allergic sensitivity to these substances. Infants with eczema are therefore much more likely to develop food allergy, respiratory allergy and asthma.


Eczema therefore predisposes an individual to developing allergies and not the other way around as previously thought. Once the patient develops allergic sensitivity to an allergen, exposure to that allergen through direct contact or ingestion then leads to allergic inflammation in the skin. Inflamed skin is dry, intensely itchy, rough and can become infected easily. Common allergens that can cause atopic dermatitis include food, house dust mites, chemical substances found in skin care products, rubber chemicals, metals, and even sweat and bacteria that live on the skin.

Reference information:  http://www.allergy.hk

The information aims to provide educational purpose only. Anyone reading it should consult physician before considering treatment and should not rely on the information above.