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.

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.

Treatment of atopic dermatitis should first and foremost include repairing the skin barrier function to reduce allergen penetration. This can be accomplished by the regular use of barrier ointments. 

Food allergy is often an important factor in patients under the age of three, but diagnosing allergy in atopic dermatitis is full of pitfalls. These patients generally have very high total IgE antibody levels, rendering the use of allergy blood tests unreliable; in the presence of a large amount of IgE, non-specific IgE binding occurs and a large number of false positive reactions are seen. Many patients erroneously go on diets avoiding many foods based on these findings, whereas most patients are only allergic to less than three kinds of food. Skin prick tests are more reliable, but only if done during disease remission. Skin tests performed on inflamed skin will also result in a large number of false positive reactions. We therefore always treat the dermatitis first and do allergy tests once the disease is under control. 

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.

What is allergy?

An allergic reaction occurs when our immune system reacts to otherwise harmless substances from outside our body. Our immune system has an important role in protecting us from infections. It normally recognizes bacteria, viruses and fungi by reacting to their proteins (antigens), but only under circumstances that present danger to our body such as tissue damage. In the absence of such “danger signals”, foreign proteins are usually recognized as harmless and are tolerated. This process of immune tolerance occurs the first time our immune system comes in contact with these foreign proteins, such as when an infant ingests milk formula or breathes in pollens for the first time. However, if immune tolerance to a particular antigen fails to develop or is lost, the individual then becomes sensitized to this antigen and develops antibodies and specific T cells against it. An antigen that causes allergic sensitization is called an allergen. When the individual is exposed to this allergen again, an allergic reaction occurs.

Allergic symptoms can be caused by different immunological mechanisms. The majority of allergic diseases are caused by either the Type I (or immediate-type) hypersensitivity response, or the Type IV (or delayed-type) hypersensitivity response.

Immediate-type hypersensitivity reactions are caused by antibodies called IgE produced by the immune system against allergens such as pollens, house dust mites, mold spores, animal dander, insect venom, food or drugs. When the patient is exposed to these allergens, the IgE attached to allergy cells called mast cells binds to the allergens and trigger the mast cells to release chemical mediators such as histamine. This leads to swelling, itching, redness, congestion and airway constriction within a matter of minutes. Mast cells are mostly found in the skin, respiratory tract and gastrointestinal tract. IgE antibodies are involved in causing nasal and ocular allergy, asthma, insect sting allergy and some types of food allergy and drug allergy.

Delayed-type hypersensitivity reactions are caused by a type of immune cells called T cells. Each T cell specifically recognizes one allergen, and when it is exposed to this allergen, it becomes active and produces chemical mediators that cause inflammation. This type of reaction usually occurs 24 to 72 hours after allergen exposure, and tends to become chronic. Certain types of food and drug allergy, contact dermatitis and atopic dermatitis are caused by this type of reaction.

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.