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 Asthma?

Asthma is a common condition that affects more than 10% of the population. Asthma is defined as reversible airway obstruction. It is caused by narrowing of the lower airways due to inflammation, and is therefore a disease of airway inflammation. Asthma patients might be normal most of the time, but when the disease exacerbates, the patient would cough, wheeze, and feel tight in the chest and short of breath.

Asthmatic tendency is genetically determined, but the disease is triggered by external factors. Asthma most commonly starts during childhood, and the two most common causes are allergy and infection. Before the age of three, asthma is more commonly caused by virus infection, and the most common culprits are Respiratory Syncythial Virus (RSV), Rhinovirus and Adenovirus. Acute infections with these viruses can lead to croup, and patients develop high fever, cough, wheezing and dyspnea. In susceptible individuals, croup during the first two years of life can subsequently lead to recurrent wheezing illnesses.

However, this problem often improves with age and goes into remission by about 8 years of age. Allergic asthma, on the other hand, often persists into adulthood. Even in those patients who seem to outgrow their asthma during their teens, recent studies have shown that many of them will develop asthma symptoms again in their 30s and 40s. The majority of patients with allergic asthma also suffer from allergic rhinitis, since both conditions are caused by allergen exposure. The most common allergens include house dust mites, cockroach, animal dander, mold spores and pollens.

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.

花粉過敏 - 敏感的原因

時常聽到身邊的朋友患上鼻敏感、哮喘或濕疹。這些常見的問題全因接觸環境致敏原而引起，所以，如何避免接觸致敏原是一個重要的範疇。致敏原有多種，常見的包括塵蟎、動物毛屑，真菌、霉菌孢子及花粉等等。

花粉

花粉敏感是室外的問題，一般引起敏感的花粉以樹、草、雜草花粉為主。香港的氣溫較為溫暖，沒有由冬入春夏的花粉季節，因此花粉的數量不多；不過，在某些地方可能會有較多的花粉數量，如山谷環境。當空氣不流通時，花粉便會在空氣中逗留一段較長時間，並隨風而擴散。

預防花粉敏感

對花粉敏感者，在進行戶外活動時，特別是打高爾夫球或在草地踢足球，都有機會引起過敏反應。如患者接觸花粉後，便容易引起蕁麻疹（風疹）、鼻塞、打噴嚏，甚至哮喘的情況；至於室內花粉，多由室外傳入，所以減少接觸花粉的方法跟霉菌的一樣，把窗關好並開放冷氣，要注意冷氣系統亦需要使用高效率的過濾網減少室外的花粉傳入。

參考資料: www.allergy.hk, 《了解過敏症》

以上所提供的資訊僅作為教育及參考用途，如果你有任何醫療問題，應向自己的過敏病科醫生查詢，而不應單倚賴以上提供的資料。

愈乾淨、愈過敏？

參考資料: www.allergy.hk, 《了解過敏症》

近四、五十年，過敏症的發病率急劇上升，按早前美國的研究數據顯示，1940年代的過敏症發病率大約5%，到了21世紀已增加至25%。是什麼因素令過敏症迅速漫延？

根據衛生學的假說，這是由於現代社會的環境衛生做得太好、太徹底所致。當中更指出，若在兒童時期接觸細菌和病毒的機會太少，相反會令他們的免疫系統對一些無害物質如花粉等產生過敏反應。

免疫系統與衛生環境

過敏症是免疫系統對致敏原產生的不正常反應。過敏症、免疫系統和外在環境三方面的關係是密不可分的。嬰兒自出生後的兩至三年，他們免疫系統的成熟速度會受到環境所影響，而人體免疫系統的成熟速度快與慢，是直接影響過敏症的現象。

所以，生活於多病毒、多細菌的環境下，人體的免疫系統經常受到刺激，使其加快成熟，產生過敏症的機會便會較少。相比發達國家，生活環境乾淨衛生，傳染病控制能力強，但免疫系統成熟速度相對緩慢，再加上多種抗生素、預防性疫苗等，這一切一切都有可能增加過敏症的機會；正如德國的一項研究發現，農場與城市長大的兒童，他們日後患有敏感和哮喘的機會並不一樣，城市長大的兒童比前者的高出一陪；此外，在農場生活的兒童因時常接觸動物，而動物身上滿佈細菌，這些細菌的抗原會令兒童的免疫系統成熟速度加快，從而減少患上過敏症。

以上所提供的資訊僅作為教育及參考用途，如果你有任何醫療問題，應向自己的過敏病科醫生查詢，而不應單倚賴以上提供的資料。

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.