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House
dust mite
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The
house dust mite
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How
to avoid it
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Does
it help to avoid it?
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Allergic
rhinitis guideline
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The
house dust mite is an important cause of
symptoms for patients with asthma, eczema,
rhinitis and many other conditions.
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More
than one kind of dust mite protein may be
responsible for causing the allergic reaction, and
it may not be the dust mite, but its droppings that
are the source of one of these proteins. The dust
mite is a little bit smaller than the very tiniest
dot that the human eye can see. Imagine the very
tiniest dot that you can make with a very sharp
pencil and you will realize that a dot not much
smaller than this would be invisible. This is then
about the size of a dust mite. So it is not possible
to tell by looking whether your bedding, carpets and
upholstery contain them. Sometimes there can be as
many as several thousand in one gram of dust.
Dust
mites are found where humans spend most of their
time, but only in temperate climates. Why is this?
It is because they like the same conditions of
warmth and moisture as we do, and they live on the
tiny scales of skin that we constantly shed.
So
what can we do about it?
How
to avoid the house dust mite
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Good
ventilation and low humidity
Anything
that you can do to get fresh air circulating the house will help. In particular leave a
window slightly ajar in the bedroom at night, with the bedroom door shut. Make sure there is
adequate ventilation when cooking and bathing, and do not dry washing in the living areas
(e.g.
in front of the radiator).
If your house has a condensation problem, consider asking for
professional help in resolving it. In some cases a ventilation system that extracts air
from environments in which there is high humidity can be an
advantage. The aim should be to reduce indoor relative humidity to below
50%.
When dusting, use a slightly damp duster, not too damp as the dust mite
thrives on moisture. The slight dampness will prevent the dust from becoming airborne.
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Vacuum cleaning
The
problem with old-style vacuum cleaners is that they are inefficient filters of the fine dust
particles of mite droppings that cause the problem. This fine dust, invisible
to the naked eye, is pushed back into the room from the cleaner's exhaust. This means that
vacuum cleaning with an inefficient cleaner can be worse than not vacuuming at all as the fine
dust particles become airborne after vacuuming.
Specialized cleaners are now available
and more are coming on to the market all the time. They incorporate a
high efficiency particulate air (HEPA) filter
to ensure that the air returning to the room is free from the very fine particles. Before you
spend a lot of money on a new cleaner, remember that vacuum cleaning on its own
will not solve the house mite problem, although if you are using the wrong kind
of cleaner, you are likely to making the problem worse rather than
better by using it. |
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Pillows and
duvets
Ask most people when they last had their
pillows, duvets and cushions washed, and most will admit that it is only the covers that ever
get washed. For even better control combine regular washing with full zip-shut
dust mite proof barrier covers to
pillows, mattresses and duvets. Ideally you should apply the covers to new mattresses, duvets, pillows or cushions. They
will, however, still be effective if applied to old ones, preferably after washing (or after
thorough vacuuming for the mattress). At present there is no standard test to compare
covers, although from 1998 all covers were required to carry a CE Mark (European Commission
mark of quality).
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Carpets, cuddly
toys and soft furnishings
Dust mites live
in carpets and it is far
better to remove the carpets than to try to keep them mite-free. Studies have shown that even the most
efficient vacuum cleaner only reduces dust mite counts by about
a quarter. Wooden, tiled vinyl or linoleum flooring is preferable. 
If rugs are required, these should not be of the ‘pile’ variety
– open weave types are preferable. These should be taken
outside to be beaten and aired in sunshine (three hours of strong
sunlight removes dust mites) at intervals. Heavy or lined
curtains also accumulate high levels of dust mites; use lighter and
unlined ones that can be washed regularly. Soft toys can be a
big problem, especially if they share a child's bed. Washing
monthly at temperatures above 60 degrees Centigrade (or placing in
the freezer overnight in a polythene bag) will control the problem.
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Chemical
sprays and powders
The
benefits of using chemical measures (dust mite sprays and granules) remain
unproven, and they are likely to be expensive if used adequately and as
the sole method of dust mite control.
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Dehumidifiers
Whilst
these sound like a very good idea, in practice, studies have not shown that they help reduce
dust mite levels. However, they may be helpful in controlling the
levels of indoor mould spores.
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Does it help?
An important question that concerns
allergists and their patients is whether the measures we advise regarding the control of the house
dust mite do actually help patients suffering from dust mite allergy.
As you might imagine, studies that put these measures to the test
are difficult to undertake, and for that reason we do not yet have all the evidence. In
particular, patients my have several allergens to avoid and it is impossible to
design a suitable study when each trial patients may other allergies in addition
to dust mite allergy. The dust mite is also associated with several different
conditions, and no single piece of research can do
much more than answer one of these at a time. Academic departments of allergy, and the prestigious
Cochrane
Collaboration review medical research topics such as this to provide doctors and
patients with a balanced view of the available research evidence.
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Indoor
exposure to house dust mite (HDM) allergens is very high not least because people spend 90%
of their time indoors. Minimising the impact of environmental risk factors such as
the house dust mite
is an important step in reducing the severity of asthma Custovic et al,
2002 |
The doctors who reviewed the
available evidence for the Cochrane Collabration have called for more studies to be done. In particular, patients wish to
know not only will the avoidance help the symptoms they have now, they wish to know if the
avoidance will help to prevent their disease from getting worse.
While we are waiting for the
answers to these questions, to most people it makes sense to avoid the cause of their allergy.
As one patient said:
'If my finger was burning because I was holding it in a flame, I would
certainly remove it from the flame before deciding if I needed further treatment'.
House
dust mite avoidance in allergic rhinitis
The
guideline of the British Society for Allergy and
Clinical Immunology recommends allergen avoidance as
a first step in treating nasal allergy (allergic
rhinitis).
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"Skin
prick tests should be carried out routinely in all cases and must be
interpreted with a clinical history. This is important as the tests are
known to have a high negative predictive value and 15% of patients with
positives outcomes do not develop symptoms upon exposure to allergens" |
"Exposure
to house dust mites is a major cause of perennial
rhinitis. Steps for treating allergic rhinitis begin
with taking the patients clinical history combined
with skin prick testing/serum specific IgE blood
tests and allergen/irritant avoidance along with
nasal douching. If symptoms continue selected
medication should be prescribed as listed in the
published guideline.
Allergic
rhinitis is predominant among children and accounts
for about a third of rhinitis cases in adults. It
significantly reduces quality of life and interferes
with both attendance and performance at school and
work.
Standardized
allergy education improves disease specific quality
of life. Treatment of rhinitis is associated
with benefits for asthma. Most asthmatics have
rhinitis. House dust mite avoidance for clinical
benefits is most likely achieved with multiple
interventions such as mite proofing beds, removing
carpets and upholstered furniture."
BSACI
guidelines for the management of
allergic and non-allergic rhinitis
Scadding
et al, 2008
Recommended
Website
housedustmite.org
Everything you need to know about the house dust
mite and its relation to asthma, rhinitis and eczema.
u
www.housedustmite.org
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