House Dust Mites (PDF)
Most people with asthma find that a number of provoking factors (trigger factors) cause them to have attacks or make their asthma worse. A common trigger factor for asthma is the house dust mite.
What are house dust mites?
House dust mites are microscopic creatures roughly one third of a millimetre long. They thrive in their thousands in warm moist places, feeding on dead skin.
The most common place to find dust mites are in beds and carpets. It is the mites’ droppings which readily become airborne, and when inhaled, can provoke a strong allergic response. These droppings are distributed in the dust in all parts of the house.
Dust mites can produce up to 200 times their own weight in droppings in their lifetime. They are extremely sensitive to dry conditions and changes in temperature.
The house dust mite population is high around the coastal areas of Australia and scarcer in drier inland places.
How is asthma that is triggered by house dust mite treated?
It is important to reduce trigger factors and reduce exposure to house dust mite rather than relying solely on medication for control.
If you or your child’s asthma has shown to be triggered by house dust mite, it is best to concentrate on reducing the dust mite from carpets and bedrooms.
Remember that most allergens remain trapped in beds and carpets, and only a small proportion become airborne.
Precautions you can take to decrease dust mite numbers:
1. Keep bedrooms well ventilated and well lit with natural light if possible.
2. Use dust mite proof mattress, doona and pillow protectors. Clean the covers regularly as recommended by the manufacturer.
3. Hot wash (greater than 55oC) bedding e.g. sheets, pillow cases and quilts, in soapy water at least once every two weeks. Cold water does not kill dust mite. Alternatively wash with a mix of three parts detergent and one part Eucalyptus oil or Tea Tree oil.
4. Air blankets weekly, where possible in natural sunlight.
5. Showering before going to bed is thought to be of benefit.
6. Vacuum the mattress and any upholstered furniture weekly. More frequent vacuuming has shown to be of little benefit.
7. Carpets need to be vacuumed twice a week. Vacuum cleaners with HEPA filters, Tri-level internal (or triple) filters and Electrostatic filters are the most effective against airborne allergens.
8. Put fluffy toys in the deep freeze once every 2 weeks, for 4 hours or overnight.
9. Damp dust weekly. This is more beneficial than feather dusting. Dust mite allergen is water-soluble. To prevent allergen being spread whilst cleaning all water used should be changed regularly.
10. Minimise the number of items stored under beds and on top of wardrobes so that regular cleaning can occur.
Some points to be considered:
1. Fluffy toys should not be kept on the bed. It is preferable to buy toys that are not fluffy.
2. Avoid having carpets in the house or at least in the bedrooms. Timber and vinyl coverings are preferred along with other hard coverings, as they are easily cleaned.
3. Where possible, buy wooden, vinyl or leather furniture. Upholstered furniture can harbor the mite. If you have upholstered furniture, vacuum it weekly.
4. Carpets should be short pile since long pile carpets hold more dust. Carpets can be wool or synthetic. The person with asthma should try to avoid doing the vacuuming. However, if this is unavoidable, weekly vacuuming should be performed with the windows and doors open. Some people may also need to wear a face mask.
5. After vacuuming, leave the house and allow the dust to settle for a half an hour or so before re-entering.
6. Wet and steam cleaning removes the mite from carpets more readily than vacuuming. However, research suggests that it only improves it by two thirds and the residual water left in the carpet may promote fungal growth.
7. Air filters are thought to have little effect on reducing asthma symptoms.
8. Dry cleaning kills the mites but again has little effect on the level of mite droppings which is the aggravating allergen.
9. Chemical control methods show only a moderate control of the allergens. The chemicals kill the mite but do not remove the allergen (the droppings). There is some concern regarding its overall toxicity.
10. Choose window coverings that can be easily cleaned.
11. Sheepskin products are best avoided, but if their use is essential, wash in hot water (55oC) or place in the deep freeze for at least 4 hours or overnight every 2 weeks.
12. Remember that dust mite allergy is to the faeces, just killing the mites is not enough and the item should also be washed.
It is important to remember that improvement of asthma symptoms occurs as a result of massive reduction in dust mite allergens.
We appreciate that this is difficult and that the above methods may only aid in reducing levels slightly. Skin testing for the dust mite and other allergens is most useful for patients with chronic/severe asthma.