Dust Mites

One of the most highly allergenic contaminants found indoors is house dust, often heavily contaminated with the fecal pellets and skins of dust mites. Estimates are that dust mites may be a factor in 50 to 80 % of asthma cases, as well as in countless cases of eczema, hay fever, and other allergic ailments. Common causes of allergy and asthma symptoms include house dust mites, mold, cat dander, cockroach droppings and grass pollen.

Usual symptoms are respiratory in nature, usually not a rash. However, there are reports of a red rash around the neck. The wheeze-inducing proteins are digestive juices from the mite gut and are potent allergens. An exposure to the mites in the first year of a infants life can trigger a lifelong allergy.

One must control the levels of dust mites. Beds are a prime habitat, a typical mattress may have anywhere from 100,000 to 10 million mites inside. Mites prefer warm, moist surroundings such as the inside of a mattress when someone is on it. Their favorite food is dander (human skin flakes). Bedroom carpeting and household upholstery usually support high mite populations.

Dust mites are about .01 inches (250 to 300 microns ) in length and have translucent bodies, so they are not visible to the unaided eye. For accurate identification, one needs at least 10X magnification. Through a microscope, one will see many oval-shaped mites scuttling around and over one another. There are eight hairy legs, no eyes, no antennae, a mouthpart group in front of body (resembles a head) and a tough, translucent shell, giving a "fearsome appearance".

Control Measures

Recommendations focus on "dust control". One must reduce the concentrations of dust borne allergens in the living environment by controlling both allergen production and the dust which serves to transport it.

Keep the house clean Dust mites, pollens, animal dander, and other allergy symptom triggers can be reduced, although not eliminated through regular cleaning.

Use a HEPA vacuum cleaner once a week. A high efficiency particulate arresting (HEPA) vacuum cleaner is recommended because it is much better than ordinary vacuums at trapping very small allergen particles.

Wash pillow cases and sheets once a week. Dust mites can be killed by water at 130°F (55°C) or hotter. Use non-allergenic detergent to help remove dust-mite allergens. They can also be killed by freezing.

Keep relative humidity levels below 50 percent. Dust mites as well as other allergens thrive on high humidity. Homes with air conditioning constantly have lower mite counts then non-air conditioned homes.

Use a high efficiency air filter. Most of the cheap ordinary air filters an not capable of trapping mites and their by-products. One should also look for a filter that has anti-microbial properties, to prevent the filter from becoming a breeding ground for allergens. Filters that call themselves "washable" should be avoided because it just is not possible to wash 100% of the biological contaminants out of them and they can also become a breeding ground for microbes.

Use an allergen barrier pillow case. They creep, they crawl, they trigger allergies while you sleep. Dust mites are the leading source of allergens in the home, and their prime breeding ground is right under your nose. These microscopic, indoor inhabitants have set up camp in your pillow, the warm and humid environment where you spend one-third of your life.

House Dust Allergies: A 'Mitey' Problem

Dust mites are present to some degree in nearly all human habitation.

Allergenic proteins from dust mites were found at high levels in a recent nationwide survey of 800 American homes by the National Institute of Environmental Health Services (NIEHS):

About 45 percent of American homes have sufficient dust mite allergens to trigger allergy symptoms.
About 23 percent of American homes have sufficient dust mite allergens to trigger asthma symptoms.

In response to these numbers, James Li, M.D., a specialist in allergies, asthma and immunology at Mayo Clinic, Rochester, Minn., offers the following advice on what you can do to control your exposure to dust mites.

What are dust mites?

Dust mites are tiny organisms with eight legs, distantly related to spiders. You can't see them with the naked eye. Other than triggering allergy and asthma symptoms, they don't cause any harm. They like to live in areas that are warm and humid and can be found in many homes. Some people are allergic to dust mites' decayed bodies and fecal material, which become components of airborne household dust.

It's almost impossible to clear your house of dust, but isn't there something you can do?

There are two ways to try to control dust mite allergens in the home. One approach is to reduce dust mite proliferation by making the home environment as inhospitable to dust mites as possible. The other strategy is to reduce the amount of overall dust in the house.

How can you initiate the first strategy?

First, remember that environments that are moist — such as carpeted basements in warm climates — are perfect for dust mites. Mattresses and pillows also are excellent habitats for dust mites. If you're trying to reduce your dust mite exposure, keep indoor relative humidity low — definitely less than 50 percent. Eliminate any water leaks around the house, particularly in the basement. In addition, eliminate surfaces where dust mites can proliferate such as carpeting and upholstered furniture.

Is the bedroom of particular concern?

It is, mainly because most people spend about 8 of every 24 hours in the bedroom. As to the second approach — reducing the overall amount of dust in the house — techniques include putting allergy-proof encasements over the bedding, including the mattress, box spring and pillows. There are newer products that are somewhat more comfortable than plain plastic-bag encasements. Cotton encasements with high thread counts (260 or more threads per inch) can prevent dust mites from crawling in and out of the pillow's interior. They are available at a variety of outlets, such as furniture stores, mattress stores, department stores and medical supply stores. Wash the encasement and your pillow case in hot water (130° F.) at least once each week.

Avoid going to bed with wet hair. Moist hair and bedding attracts swarms of dust mites.

Any other suggestions?

Remove carpeting from the bedroom. Having a smooth surface on the floor helps keep dust levels low. It also can be helpful to remove stored paper, stored blankets, upholstered furniture and other dust-collecting materials.

Can air filters do much to reduce the dust mite problem?

The use of air cleaners or high-efficiency air filters is a secondary measure that can be helpful. But it's not helpful without first proceeding with allergy-proof encasements, without lowering the humidity, or without removing carpeting.

What about vacuuming carpets?

Ordinary vacuum cleaners are designed to remove fairly large particles. Vacuums stir up tremendous levels of small particles of dust, which can aggravate allergies. The best vacuum cleaners have high efficiency particulate arresting (HEPA) filters that remove most of the very small particles.

Is there a dust mite season, as with pollen or molds? Are the summer months tougher on people with dust mite allergies because of the higher humidity?

The dust mite season is actually quite erratic. It may be higher in the summer in many climates because of the warmth and higher humidity. But people who are sensitive to dust mites often will have symptoms all year-round. And in the winter time, when people spend more time indoors and keep windows and doors closed, dust mite particles are often still in the house, and they still can be a problem.

Can exposure to dust mites actually cause the sensitivity, or are you just born allergic to dust mites?

The main area of concern is in very young children growing up in environments where there's high dust mite exposure — or other types of allergen exposure. There is some evidence that if an infant or a young child grows up where there's a high exposure to sensitizing substances, he or she will be more likely to develop allergy problems, asthma or both.

Machine Washing Removes Most Dust Mites

House dust mites -- the bane of allergy and asthma sufferers -- can be removed from sheets and clothes by washing in a machine with warm or cold water using detergent with or without bleach. Still, up to 40% of the mites will remain and repeat washings are needed to reduce contamination levels further.

Dr. Larry G. Arlian and a team at Wright State University in Dayton, Ohio, added dust mites to clothing and bedding items and then tested the cleaning ability of a residential washing machine using standard temperature settings and detergents. Items were tested in 6- and 8-lb wash loads.

The results are reported in the Journal of Allergy and Clinical Immunology. Washing removed 60% to 83% of live mites.

There was no evidence that washing with detergent alone or with beach was any better than plain water washing in removing live mites, the authors note. In 6-lb wash loads, polyester blankets retained more mites than other items, whereas in 8-lb loads cotton shirts and polyester blankets retained the most.

The type of detergent did make a difference in removing allergy-producing material shed by mites, the scientists say. Washing in warm water with or without detergent removed 84% of allergen, whereas washing with detergent plus bleach removed 98%.

The team has a word of caution. In a separate experiment, they found that live mites could be transferred from mite-infested items to mite-free items during washing.

My House is Killing Me! :
The Home Guide for Families with Allergies and Asthma

Could Your House Be Making You Ill? This book may show you why and what you can do to make your house healthier.

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--William J. Monafo, M.D., American Academy of Allergy, Asthma, and Immunology

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Control Measures