Expert Articles

Allergen avoidance in the treatment of asthma

Author: Agnes LEUNG
Assistant Professor, Department of Paediatrics, CUHK


Asthma is a chronic airway disease, especially common in children. It is estimated that there are more than 400,000 people with asthma in Hong Kong. According to a research published by the Chinese University of Hong Kong in 2007, the prevalence rate of asthma among school-age children in Hong Kong was 9.4%, that is, one in every ten children suffers from asthma. In addition, in Hong Kong, 15% of the hospitalized children were hospitalized due to asthma, and 40% of the children who visited specialist outpatient clinics were due to asthmatic attacks. On average, 70 to 90 people, mostly adults, pass away from asthma attacks every year, deaths that are caused by delayed treatment as patients do not have a proper understanding of the severity of the disease. A correct diagnosis, identification of asthma triggers and appropriate treatment are cornerstones of asthma management. 

Asthma can be difficult to diagnose, especially in young children. Diagnosis is based primarily on the child’s symptoms, their frequency, and the child’s medical history. Many childhood diseases can have symptoms similar to asthma. To further complicate diagnosis, these disorders may also be commonly associated with asthma. It is important to determine whether the child’s symptoms are caused by asthma, a disease other than asthma, or both asthma and another disease. Conditions that can cause asthma-like symptoms include rhinitis, sinusitis, acid reflux, breathing problems, and respiratory infections such as bronchiolitis and respiratory syncytial virus (RSV). In children over 5 years of age, lung function tests and exhaled nitric oxide tests can help confirm the diagnosis. 

Experiments show that allergens can cause airway hyper-reactivity and inflammation, providing evidence that allergen exposure causes asthma. Moving asthmatic individuals from their homes to a low-allergen residential setting resulted in considerable improvements in clinical symptoms and airway hyper-reactivity. 

The primary allergens fluctuate significantly depending on climate, housekeeping methods, and pet ownership. Dust mites are the leading trigger of asthma and allergic rhinitis in Hong Kong. Allergen avoidance is appropriate, mostly for symptomatic individuals who have allergic reactions verified by positive skin tests or blood assays for particular IgE antibodies. Once particular sensitivities have been identified, a detailed environmental management strategy for allergens relevant to that patient must be implemented.

Dust mites (dermatophagoides pteronyssinus and d. farinae) are Arachnida arthropods that live in beds, couches, carpets, and other woven materials. Dust mites do not bite, and other than producing allergy symptoms, they are not known to harm people. It might be difficult to educate patients about dust mites since neither the dust mites nor their debris can be seen under normal conditions. Infestation of dust mites is far less prevalent in dry and high-altitude settings. In locations with lengthy, harsh winters, interior conditions are so dry that dust mites are often absent. 

Dust mite faeces include a complex mixture of allergenic dust mite-derived proteins, all of which activate your immune system. These particles are rather big and heavy, and they become airborne only briefly following intense disturbances, and settle quickly, such that no allergen is found in the air within 15 minutes. As a result, air filtration has only a limited role in dust mite exposure reduction. 

Avoiding dust mites has been proven to reduce symptoms as well as airway hyper-reactivity. Since exposure is thought to occur mostly through close closeness to dust mite detritus when in bed, on the floor, or on upholstered furniture, mite-proof bedding has been demonstrated in research studies to reduce acute episodes of asthma that require hospital care in children with a history of repeated severe attacks. Plastics can be used to cover furniture cushions, mattresses, and pillow coverings, but some patients may find this material unpleasant. According to research, finely woven materials with pore diameters as tiny as 2 microns can effectively restrict the passage of dust mite and cat allergens while allowing appropriate air passage. Weekly to biweekly washing of sheets, pillow covers, mattress pads, and blankets successfully lowers dust mite counts; however, washing should be done in hot water and preferably dried in an electric clothes dryer on a high setting.

To diminish the sites where dust mites might colonize, efforts should be taken to limit the presence of carpets, upholstered furniture, and draperies in the surroundings of the dust mite-allergic individual. Dusting surfaces and vacuuming floors on a regular basis should be done using a vacuum fitted with a high-efficiency particular air (HEPA) filter or with double thickness bags. The number of stuffed animals in children’s bedrooms should be kept to a minimum. Dust mite presence may be reduced by lowering humidity, and keeping relative humidity below 50% is suggested. 

Besides allergen avoidance, asthma can be treated with different types of medicines. The major treatment includes quick-relief medicines (such as short-acting beta agonists) but should only be used once in a while. If a child requires these medicines more than twice a week, then the family should seek medical attention. The more important medicine is the long-term controller medicines (such as inhaled steroids) which control airway inflammation. Some individuals are concerned about the adverse effects of steroid inhalers, so they do not use them or give them to their children. However, the fact is that not taking a steroid inhaler is far more dangerous than whatever negative effects it may induce. Inhaled steroids prevent the development of an asthma attack, which can be hazardous and even fatal. Asthma also causes lung damage over time, but the inhaled steroid can prevent this damage.  

Asthma, once treated appropriately, should not prevent children from doing normal activities such as playing sports, miss schools or damage their lungs. 

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Allergen avoidance in the treatment of asthma