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Airborne asthma triggers
Identification of allergic
triggers is an important aspect of asthma care and leads to improved management and better
quality of life. The significance of a a particular allergic trigger in a particular
patient may be suspected by taking a careful allergy
history. Dust mite allergy is an important trigger in chronic asthma
and should be considered if symptoms occur or get worse at night, when exposed to vacuuming or
bed making, or when asthma gets worse in dusty or damp premises (dust mites thrive in damp
conditions). Asthmatic symptoms that occur in relationship to animals are usually more
easily identified. However in severe cases, symptoms can be provoked when the sufferer
gets wheezy when they are exposed to the clothing of someone who handles horses or who has
recently ridden a horse.
Exposure to an allergen or to a chemical fume present in the sufferers
workplace must always be considered. This can be surprisingly difficult to detect and it
there is more than a suspicion that this is an overlooked cause of chronic asthma. Often
the only clue may be when symptoms clear up with a prolonged holiday, only to recur within a
few hours of starting work again. Keeping a regular record of the peak
flow rate may be the best way to establish a relationship between going to work
and the degree of airway narrowing.
Allergy to the fungal spores alternaria
or cladosporium is an important cause of severe
seasonal asthma in the late summer and autumn. Patients with this type of allergy may
have severe episodes of asthma at the same time each year, and may even require hospital
admission. However the fact that there is a potential environmental cause of the problem
usually goes unrecognised, unless the patient is seen by an clinical allergist. An
awareness of these and other allergen triggers can allows preventive treatment either by
avoiding the troublesome circumstances, or at least ensuring maximal prophylactic measures
(e.g. adequate preventer inhaled steroid) at
the appropriate time.
Potential airborne allergic triggers of asthma occur in the following
groups:
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Allergy
- to house dust mites, grass and tree pollens, animals, birds, and mould spores (this kind
of sensitivity does normally show up with allergy tests).
-
Occupational and
domestic dusts and fumes - particles from latex gloves, dust from insects,
animals, beans, wood, flour grain and hay. Fumes from glues, resins and soldering.
Certain chemical compounds from glues and resins, paints, plastics, particle boards,
especially isocyanates (this kind of sensitivity may or may not show up with
allergy tests)
House Dust Mite
The house dust mite is
the most important single known allergen involved in the causation of asthma in the UK. Both
the incidence and the severity of asthma are known to be linked to the level of dust mite
exposure; older homes, older carpets and mattresses, damp and condensation are all associated
with higher levels of mite allergen. In a recent study two out of three British homes
were found to have dust mite allergen levels sufficient to be associated with an increase in
the risk of asthma.
It is the mite droppings
that are the main source of the problem. Faecal pellets, disturbed by human movement,
are pushed into the air. They then remain suspended in the air to be inhaled. Digestive
enzymes in the droppings appear to be the source of the problem, attacking the protective
lining of the lungs, nasal passages or lining of the eyes of allergic people.
Whilst the taking of half-hearted measures to control
the numbers of mites is likely to make little difference, there is now good evidence that the
use of the correct measures successfully reduces dust mite levels. Whilst there has been
some disagreement about whether this will actually help asthma there is general agreement that if the measures taken are to do any good, they
need to be rigorous. For example, it is no good vacuuming and ventilating the bedroom and
covering pillows and mattresses unless the pile carpet is removed. In short, this is a
job that if worth doing, is worth doing well.
more . . .
Cats
Dust particles arising from cats are another important
trigger for asthma. Although in the UK they are not as quite as important as the dust
mite, in some countries the cat is the most predominant single asthma trigger.
However, for asthmatics who know they are allergic to
cats, it makes sense to try to reduce exposure.
more . . .
Fungal (mould) Spores
Inhaled fungal spores are a well-known cause of allergy
and asthma. Indeed in some places the rate and severity of asthma in the population have
been linked to airborne levels of the mould spores alternaria and cladosporium.
Exposure to fungi is also known to be capable of causing
asthma in other ways. Occasional patients can be shown to have evidence of a fungus
present in the lung (for example, discovered when their sputum is cultured) and then have
severe asthma symptoms as a result, a condition known as bronchopulmonary aspergillosis.
Treatment with antifungal drugs may then be helpful.
Even more intriguing is the very occasional asthmatic
patient with an athlete's foot infection who is found to be allergic to the fungus causing
it, and who responds to antifungal treatment with clearance of not only the athlete's foot, but
also the asthma. Fungal foot infections are also very occasionally thought to cause chronic
urticaria or angioedema in a similar way.
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Allergy Clinic
