House Dust Mites : Allergy to House Dust Mites (HDM) is indeed a very common phenomenon. In fact, HDM play a very important role in causing allergic rhinitis (AR), bronchial asthma and eczema. How Do You Know You Have HDM Allergy ? While spring-cleaning your room, sweeping the floor, changing the bed sheets, dusting your old favourite story books, or entering a dusty environment, you suddenly begin to feel that your nose is blocked and runny. Your eyes are itchy and tears roll down as you sneeze violently. You may well have an allergy to dust or more accurately… dust mites. Upon consulting your doctor, he/she suspects that you have HDM allergy. Of course, additionally, HDM allergy can also be confirmed with a skin prick test (SPT) or a blood test, as advised by your doctor. Know Thy Enemy ! The 3 commonest HDM are called: • Dermatophagoides pteronyssinus, • Dermatophagoides farinae • Blomia tropicalis Now, how big or rather, how small are they? Imagine this… • Paper thickness is about 100 microns (or 0.1 millimeter). [1 micron or micrometer =  a millionth of a meter.] • The diameter of human hair is about 40 -120 microns. (0.04-0.12 millimeter) • A typical HDM is about 250-300 microns (0.25-0.3 millimetres) in length and width. Due to their very small size and translucent bodies, HDM are not visible to the unaided eye. Our   warm   and   humid   tropical   climate   is   also   very   suitable   for   the   HDM   to   thrive   very   well. They   grow   best at   humidity   about   70%   and   temperature   above   23   C. A   mated   female   HDM   can   lay   60   to   100   eggs   in   the last   5   weeks   of   her   life.   In   a   10-week   life   span,   a   HDM   will   produce   approximately   2,000   allergenic (substance   that   can   induce   an   allergic   reaction)   faecal   particles   and   an   even   larger   number   of   partially digested   enzyme-covered   dust   particles. The   faecal   material   is   then   inhaled   into   our   airways,   resulting   in allergic response in our airways (nose, throat, lungs). So imagine the number of HDM on your mattress and your bedroom ! Millions ? Trillions?! They are everywhere… A gram of dust can contain up to 1,000 HDM and 250,000 faecal droppings ! As if that is not bad enough, our shed skin squames/scales provide the main food supply for the HDM ! In fact, 2 of the 3 commonest  types of HDM are named after this habit -'Dermatophagoides' actually mean "skin eaters" ! We   also   spend   about   1/3   of   our   every   day   in   our   bedroom,   making   avoidance   of   these   HDM   and   their allergenic   material   almost   impossible.   However,   much   can   be   done   to   minimize   your   exposure   to   these creatures.   Therefore,   if   you   have   allergy   to   HDM,   it   is   important   to   effectively   reduce   your   exposure   to the HDM. While compliance to medication is essential, these environmental measures will help to reduce your contact with the HDM too. Remember, not only must you kill the live HDM, you must also remove their allergenic waste product, even if the HDM is already dead ! DO NOT UNDERESTIMATE THESE ENVIRONMENTAL MEASURES. (speaking from personal experience as a patient) as they can be very helpful to improve your allergic symptoms. Ways to Reduce HDM Exposure: Reduce Indoor Dust • Clean and wipe the room regularly -Wet-mop and vacuum frequently to minimise dust collecting, especially areas prone to dust collection. eg. above the fan blades Wear face mask during cleaning to avoid inhaling allergens. • Use vacuum cleaners that have high-efficiency particulate arresting (HEPA) filters installed. Conventional vacuums are very "inefficient." Vacuuming is only effective for removing dead mites and HDM faecal particles. The live HDM can resist eviction as they possess claws that allow them to latch on tightly or they might also burrow deeper into the material. Furthermore, you will merely be displacing the dust particles as it escape airborne from the other end of your vacuum cleaner into another part of your room. Water-based vacuum cleaners are also not advisable as they have been found to have extremely poor filtration. • Change bed linen every week, pillow cases daily and wash bedding in hot water (>60oC) every 2 weeks to kill mite. Alternatively, encase pillows in zippered, dust-proof covers. • Replace woollen blankets with nylon/cotton cellulose ones. • Remove carpets, rugs and replace floor with hard wood, vinyl or tile. • Remove thick elaborate curtains, venetian blinds, drapes, wall hangings and other dust accumulators (eg. potpourri flowers, picture frames). Use window shades instead. • Redesign your room and/or rearrange your furniture so that the room is easy to clean and clutter-free. Hidden and hard-to-clean corners accumulate dust naturally. • Tuck away infrequently-used personal items in a closed shelf/cupboard. • Replace soft toys (eg. teddy bears) with metal, wooden and plastic ones or alternatively… If separation is too painful for the child (or even adult !), use only washable soft toys -tumble stuffed animals in dryer weekly on hot cycle or .. keep the soft toys in a clear plastic bag. • Use anti-dust mite pillows and mattress covers. This range of beddings employs tightly-woven microfabric that blocks allergen. Wash mite-proof beddings at least every 6 to 8 weeks • Permethrin-impregnated bedding material can be an option to reduce exposure to HDM. • Use electrostatic or high-efficiency particulate arresting (HEPA) filters. -HEPA filters trap particles as tiny as 0.3 micrometers (µm)/ microns in diameter with an efficiency rating of 99.97%. • Medical-grade "True HEPA" filters, known to be even more efficient than HEPA filters, are also available in the market now. True HEPA is the highest grade of filtration Reduce Indoor Humidity (< 50%): [HDM survives well in environment of higher humidity and warmer temperature.] • Install an air conditioner, dehumidifier. Keep the room humidity at about 40-50%. • Eliminate/minimize indoor plants. They increase the moisture in the room • Ventilate home -open the windows regularly for exchange of fresh outside rather than recirculating stale air. Some direct sunlight for at least for 3 hours would be useful. Reduce Indoor Pets: • People allergic to their pets should remove the animals from the house, if possible, or at least keep the animals out of the bedroom. Wash pets frequently to minimize the amount of allergens on their skin. The HDM also feed on the squames/scales from the pets. Use approved pesticides for HDM • acaricides (e.g., benzyl benzoate -Acarosan®) to kill HDM, and • antigen-denaturing agents (e.g., tannic acid).

Blomia tropicalis -a common house duct mite - so tiny that it is invisible to the naked eye

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Ways to reduce house dust mite exposure (English language)

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This patient education is provided in good faith to help patients and their families learn more about their medical conditions, the options available to them and the possible consequences of their decisions. This information is not intended to be used for diagnosis, or treatment of any specific individual. Please consult with your ENT doctor regarding your particular circumstances.

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Ways to reduce house dust mite exposure (Bahasa Malaysia/Malay language)

Last update:  10/5/14 

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