Dust allergy is actually a sensitivity to substances in the waste particles and body fragments of house dust mites. While almost everyone is irritated by exposure to large amounts of dust, only some people have a true allergic reaction to house dust. This true allergic sensitivity is just as real and just as specific as an allergy to ragweed, tree pollen or cat dander. It may cause nasal symptoms, eye inflammation, throat clearing, asthma, eczema, hives and even gut sensitivity resulting in gastric reflux and food intolerance.
Dust mites are microscopic creatures that live in pillows, mattresses, blankets, carpets and other soft materials. They are often thought of as insects, but are actually tiny arachnids, relatives of spiders and ticks. They do not live on people, but live near them. Their food is the dead skin scales that we all shed every day.
Dust mites avoid the light, and require at least 50% relative humidity to survive. They are therefore plentiful in soft materials, such as pillows, mattresses and blankets, where they can burrow into the fabric to get away from the light. Beds provide the warmth, darkness, high humidity and shed skin scales that mites crave, and they are the source of the biggest mite exposure for most of us. A mattress may contain over a million dust mites. A female mite lays about 60 eggs in her lifetime. Each mite lives for about 80 days, during which time it produces one thousand allergy-causing waste particles.
Live mites themselves are not inhaled. Rather, it is the waste particles that they have produced, and the body fragments of dead dust mites, that become airborne, are inhaled and cause allergy symptoms. This is because mites do not live in the air, but are burrowed in soft materials. Mite waste particles become briefly airborne when one walks on a carpet, sits on an upholstered chair, places one’s face on a pillow, makes a bed, or otherwise disturbs the soft materials where the dust mites are living.
Efforts should focus on the bedroom, where mite numbers are highest, and where most people spend a third of their life. Steps should be prioritized, taking first those actions that are relatively easy, but that produce large decreases in exposure.
Start with the Bedroom
- Encase pillows, mattress and box spring in allergen impermeable covers, to prevent mite allergens from escaping and being inhaled. An alternative is to purchase a new pillow manufactured with an allergen barrier outer fabric.If there is more than one pillow on the bed, all of them should be encased, or replaced with barrier fabric pillows.
- Use washable blankets, and wash all bedding in hot water every 2 weeks. This will kill any live mites, and also wash out accumulated allergen.
- Replace comforters with a special comforter manufactured with an allergen-barrier outer fabric. Since such comforters can not be colonized by mites, they need not be washed frequently.
- If possible, remove the bedroom carpet, leaving a wipeable floor (hardwood or tile). Washable throw rugs may be used, if washed every 2 weeks in hot water.
- Remove stuffed toys, throw pillows, pennants, upholstered furniture, and other non-washable, non-wipeable items from the bedroom. Washable toys may be kept in limited number if they are hot water washed regularly.
Control Your Air
- Keep humidity below 50% to prevent dust mite growth entirely. Lesser decreases in humidity still suppress dust mite growth and allergen production somewhat. Use air conditioning in the summer, supplemented with an additional dehumidifier.
- Avoid using a humidifier in the winter, or if one is used, monitor humidity with a gauge, and keep relative humidity below 45-50%.
The following steps are of questionable benefit, and we cannot recommend them based on current information:
- The role of chemical treatment of mites in carpets is unclear. Benzyl benzoate works very well in the laboratory to kill dust mites on contact, but has not been shown to decrease mite allergen levels in homes enough to decrease symptoms. Tannic acid does not affect the mites themselves, but works to inactivate the allergen in their waste particles. It is less effective and shorter lasting than previously believed. Neither of these is recommended by the current National Heart, Lung and Blood Institute guidelines.
- Air cleaners, although widely used, have not been shown to be of significant benefit for mite allergy. This is probably because mite allergens in the air settle to the floor within a half-hour after disturbance. Air cleaners are more useful for smaller allergens, such as animal danders, which stay airborne for long periods of time.
- Studies have shown little or no allergen in hot air ducts. Hot air duct cleaning has not been shown to be helpful or needed.
Dehumidifier and dust mite encasing can reduce symptoms, but frequently inadequate for many people. The most effective treatment for chronic dust mite allergy is high dose allergy shot.
The average intact mite dropping is 10 to 40 microns in size. However, in one research paper scientists observed airborne particles containing mite allergens that ranged from 5 to 40 microns. Effective dust mite encasing needs to have a mean pore size of 1 micron or less to provide a barrier for dust mite allergens in the mattress and pillows. Here are some affordable dust mite encasings: