by David Moore
Manager of Technical Services and Board Certified Entomologist
with contributions by Eric Smith, PhD, BCE
Controlling house dust mites is a lot different than a typical pest control problem. There is really not much that your pest management professional (PMP) can do for you other than share with you the information below. This is because if you have allergies to house dust mites, this is a medical problem usually involving you being tested for being allergic to house dust mites and if you test positive, then receiving a series of shots to reduce your allergic reaction.
Most homes have house dust mites that only become a problem when an occupant has or develops allergies. The problem typically becomes a concern once the occupant visits a dermatologist, finds out they are allergic to house dust mites, and then a quick internet search reveals that the typical home has hundreds of thousands of such mites. House dust mites are responsible for allergic reactions in millions of people and may be a factor in 50-80% of asthmatics. The two most common species involved are the American house dust and the European house dust mites.
BIOLOGY or what are you up against
(from one excellent research study)
- American house dust mite. At 75°F and 75% RH, developmental time (egg to adult) required 35.6 days. Females produced an average of 66 eggs and mated females lived an average of 100.4 days, including about 63 days after egg laying had stopped.
- European house dust mite. At 75°F and 75% RH, developmental time (egg to adult) required about 34 days. Females produced an average of 68 eggs and mated females lived an average of 31.2 days, including about 1.8 days after egg laying had stopped.
- House dust mite development, fecundity (average egg production), and longevity are very dependent on temperature, moisture, and food supply. Therefore, they select only certain microclimates within a structure which provide these needs.
- These mites feed on sloughed human skin, spilled foodstuffs, fungi, and pollen. The average human sheds about 70-140 mg of skin scales daily, which is enough food to maintain mass cultures of European house dust mites for several months. The greatest accumulation of sloughed skin scales occurs primarily in bedding, mattresses, and in upholstered furniture, with much lesser amounts in carpets, and stuffed toys.
- Humans supply the necessary increase in moisture levels when they frequent these areas. Bedding and stuffed furniture provide the best conditions for dust mites.
A gram of dust vacuumed from carpeting may contain 100-400 mites, and a gram from stuffed furniture may contain about 3,500 or more mites. The estimate for a typical used mattress is 100,000 to 10 million house dust mites within it.
Can/Should Pesticides Be Used?
Since just killing the mites will not solve the allergy problem because allergies are caused by fecal material and shed mite skins in addition to live mites, the use of pesticide is questionable. Besides, very few pesticides are labeled for house dust mites. Also, most pesticides are not labeled for application to the places of highest mite concentration (bedding, pillows, and upholstered furniture). So, this is a case where the non-pesticide aspects of IPM are the most important control measures.
Vacuuming should be done with a HEPA-filter equipped vacuum that removes particles down to 0.3 microns in diameter; vacuuming without this special filter will actually make the situation worse. Such vacuuming should be done at least weekly, but will still only reduce but not eliminate the allergens; it will also reduce the mite food supply. Cleaning efforts should be concentrated in the bedroom of the allergic person, but should obviously be extended to the rest of the house. Floors should be bare, if possible. It has been shown that unacceptable allergen levels remain as long as a rug is present in the room. Hot water or steam cleaning, with or without various solutions, is not advisable because it tends to raise moisture levels.
Encasements For House Dust Mites
Encasements used for mattresses, box springs, pillows, and comforters for house dust mites are similar or identical to those used for bed bugs. Standard plastic covers are not the same and will not be effective. Zippered, washable, allergen-impermeable encasements should be used. Washable encasements should be used because allergens can accumulate in the encasement itself. These encasements should be cleaned or laundered at least monthly.
- Items that tend to trap dust such as carpets, window blinds, drapes, stuffed animals, throw pillows, and upholstered chairs should be removed at least from the bedroom, unless they are washed or laundered often.
- Down pillows and comforters should be replaced with those containing synthetic fibers.
- Lower the relative humidity to less than 45%, which will slow down mite development. The use of a dehumidifier can sometimes be helpful.
- Avoid the use of inexpensive electrostatic or ultrasonic devices that claim to get rid of dust mites. There are effective allergen-trapping filters that can be installed in heating and air-conditioning systems.
- Realize that having a dog as a pet is like adding another person to the household. This is apparently not true for cats.