House dust mites are microscopic and ubiquitous. They feed on human and animal dander, skin scales, and hair. They are frequently found in beds, mattresses, carpets, sofas, and pet bedding. Mites flourish in the home environment because the temperature and humidity are optimal for their survival (50 to 70 percent relative humidity).  

House dust allergy is common even in clean homes. House dust is a mixture of many substances. The content varies from home to home, depending on the type of furniture, building materials, presence of pets, moisture and other factors. A speck of dust may contain fabric fibers, human skin particles, animal dander, microscopic mites, bacteria, parts of cockroaches, mold spores, food particles and other debris. In human allergy sufferers, house dust is a major cause of year-round runny or stuffy noses, sneezing and itchy, watery eyes.  Dust can also cause people with asthma to experience wheezing, coughing and shortness of breath.

Hypersensitivity to house dust mites is a common problem for both animals and humans. It is difficult, if not impossible, to eliminate mites from the environment of an allergic patient. An effective environmental control regimen can help to decrease the numbers of mites and therefore minimize the patient's discomfort (see below). In addition, hyposensitization therapy (allergy vaccines) can be effective in controlling or reducing the clinical symptoms associated with mite allergy.

The following steps may help control mite populations (special attention should be given to the sleeping areas of the allergic pet):

• Avoid the use of carpeting. Bare floors, such as hardwood, vinyl, or tile are best; if carpet must be used, low pile is preferable
• Remove upholstered furniture, books, records, piles of newspapers and magazines, stuffed animals, wall hangings, and other “dust collectors” from the environment
• Use only synthetic material in the pet’s bedding. Feathers, wool, or horsehair stuffing should be avoided. Remember, cedar shavings are often a cause of allergic dermatitis in the dog
• Wash all bedding in hot water on a frequent basis
• If the pet sleeps on the bed, encase mattresses and box springs in airtight plastic. Seal the zippers on these casings with tape. Use machine washable blankets and mattress pads. Waterbeds are the most "dust-free" type of bedding available
• Plants are “dust collectors” and should be removed
• Change the furnace and air conditioning filters frequently. Electrostatic filters may be more effective in filtering out dust, mites, and inhalant particles. Specific research has not been performed on these filters and their performance in controlling clinical signs of allergy in the dog is not known
• Use air conditioning during warm months. Central air conditioning is preferred, but window units are also helpful. Try to maintain the humidity levels between 30 and 50 percent. Dehumidifiers may prove beneficial
• Vacuum floors, wet mop, and dust with a damp cloth daily. The room should be properly aired after vacuuming
• Groom the animal frequently, preferably outside of the house environment
  
  

Commonly asked questions about dust allergy

Is dust allergy a sign of a dirty house?
No. A dirty house, however, can make a house dust allergy worse. Even normal housekeeping procedures may not be enough to get rid of many of the substances in dust. Vigorous cleaning methods can also put more dust in to the air making symptoms worse.

Is house dust allergy seasonal?
In the United States, dust mite populations tend to peak in July and August, and their allergen levels stay high through December. Mite allergen levels are lowest in late spring. Some dust mite-sensitive people report that their symptoms get worse during the winter. That’s because mite fecal particles and pieces of dead mites, both of which trigger dust mite allergy, are still present. Mold levels tend to peak during the summer months (depending on where you live) and some tropical areas have molds year-round. There is also evidence that cockroaches have a seasonal pattern, peaking in late summer.

Forced-air heating systems tend to blow dust particles into the air. As they dry out over time, even more of the particles become airborne. This does not account for the seasonal pattern however, since air blows through the same ducts during the summer when air conditioning is used.

Why is mold present in house dust?
Molds are commonly found in outdoor air. However, any house can develop a mold problem given the right conditions. You might not see it growing on the walls, but it may still be present in your home. Molds require two factors to grow indoors: (1) free moisture in the form of relative humidity above 50 percent, leakage from pipes or foundation, or any ongoing source of water infiltration; and (2) something to grow on. Molds particularly like to grow on wallboard, wood or fabrics, but will grow virtually any place if given the chance.

Does house dust contain cockroaches?
As unappealing as it is, some homes do have dust that contains parts of cockroaches. This is most common in older, multi-family housing and in the southern United States where complete extermination of cockroaches is very difficult. Allergic individuals will tend to have increased symptoms when they go into such homes. Cockroaches require food and moisture to survive, so eliminating sources of each can help reduce exposure.

Contributed by: Karen Helton-Rhodes, DVM, Diplomate ACVD