Dust Mites

WHAT ARE DUST MITES?

House dust mites are microscope bugs that primarily line on dead skin cell regurarly shed from humans and their animal pets.

Dust mites are generally harmless to most people. They don't carry disease, but they can cause allergic reactions in asthmatic and other who are allergic to their feces.

Skin cells and scales, commonly called dander, are often concentrated in louging areas, mattresses, frequently used furnitures and associated carpeted areas, often harbor large number of theses microscopic mites.

Since the average human sloughs off 10 grams of dead skin aweek. That gives dust mites a lot to eat. Cats and dogs create far more dander for dust mites to eat.

A typical mattress can contain ten of thousand of dust mites. Nearly 100,000 mites can live in one square yard od carpet. A single dust mite produces about 20 waste dropping each day, each containing a protein to which many people are allergic.

The protein in that combination of feces and shed skin are what causes allergic reaction in humans.

WHERE DO THEY LIVE?

Depending on the person and exposure, reactions can range from itchy eyes to asthma attacks. And finally, unlike other types of mites, house dust mites are not parasites, since they only eat dead tissue. Gross, but true!

Beds are a prime habitat (where 1/3 of life occours) A typical used mattress may have anywhere from 100,000 to 10 million mites inside. (Ten percent of the weight of a two year old pillow can be composed of dead mites and their droppings.)

Mites prefer warm, moist surroundings such as the inside of a mattress when someone is on it. A favorite food is dander (both human and animal skin flakes). Humans shed about 1/5 ounce of dander (dead skin) each week. About 80 percent of the material seen floating in a sunbeam is actually skin flakes. Also, bedroom carpeting and household upholstery support high mite populations.

The University of Manchester performed a 2005 medical study of pillows that found up to 16 species of fungi in a single pillow. They tested feather and synthetic pillows in a range of ages, finding thousands of spores of fungus per gram of pillow ; more than is found on an average used toothbrush.

ARE THEY HARMFUL? WHAT DO THEY DO?

For most people, while they are disgusting, house dust mites are not actually harmful. However, the medical significance of house dust mites arises because their microscopic cast skins and feces are a major constituent of house dust that induces allergic reactions in some individuals.

There is a genetic predisposition to dust mite allergies, but like many allergies it can also develop over time. High levels of dust mites and their wastes, can cause previously non-allergic people to develop an allergy.  In addition to producing allergic reactions, dust mites can also cause nasal polyps growths within the nose.

Constituents of House Dust: ash, cigarette; ash, incinerator; combustion products; fiber, synthetic textile; fibers: wool, cotton, paper and silk; fingernail filings; food crumbs; glass particles; glue; graphite; hair, human and animal; insect fragments; oil soot; paint chips; plant parts; pollen; polymer foam particles; salt and sugar crystals; skin scales, humans; skin scales, pets; soil; spores, fungal; stone particles; tobacco; wood shavings   

For those individuals, inhaling the house dust allergen triggers rhinitis allergica or bronchial asthma. People with allergies to house dust usually also have allergic reactions to house dust mite fecal material and cast skins.

One of the most strongly allergenic materials found indoors is house dust, often heavily contaminated with the fecal pellets and cast skins of House Dust Mites.

Estimates are that dust mites may be a factor in 50 to 80 percent of asthmatics, as well as in countless cases of eczema, hay fever and other allergic ailments. Common causes of allergy include house dust mites, cat dander, cockroach droppings and grass pollen. Symptoms are usually respiratory in nature (sneezing, itching, watery eyes, wheezing, etc.), usually NOT A RASH. However, there are reports of a red rash around the neck. Other allergic reactions may include headaches, fatigue and depression.

The wheeze-inducing proteins are digestive juices from the mite gut which are quite potent. An exposure to the mites in the first, crucial year of life can trigger a lifelong allergy. There is no cure, only prevention. One must control house dust mite levels.

HOW TO RECOGNIZE THE SYMPTOMSOF ALLERGIES TO DUST MITES?

The protein substances in the dust mite feces produces antibodies in humans who are allergic when these are inhaled or touch the skin. These antibodies cause the release of histamines which causes to nasal congestion, swelling and irritation of the upper respiratory passages.

You may experience all or just some of them:

  • Hay fever
  • Watering eyes
  • Runny nose
  • Sneezing
  • Asthma
  • Difficulty in breathing
  • Infantile eczema
  • Itchy, red or watery eyes 
  • Nasal congestion Itchy nose
  • Roof of mouth or throat
  • Postnasal drip
  • Cough
  • Facial pressure and pain
  • Frequent awakening
  • Swollen, blue-colored skin under your eyes
  • In a child, frequent upward rubbing of the nose

A doctor can use skin tests and blood tests to confirm a suspected dust mite allergy.

Since dust mites are present all year round, the symptoms of the allergy can be present at any time of the year, but are worst  in months and seasons when the house is closed and the indoor humidity and temperatures are high (which, depending upon the household's use of heating and air conditioning, can be any time of the year). The dried dust mite feces becomes airborne when someone walks over a rug, sits down in a chair, or shakes the bed clothes, making allergic person's symptoms worse.

What else makes the symptoms worse?

  • Poor ventilation
  • High humidity
  • High temperatures (above 70 F / 20 C)
  • Indoor air pollution such as tobacco smoke or car fumes.

IDENTIFICATION

House dust mites, are too small to be visible to the naked eye; they are only 250 to 300 microns in length and have translucent bodies. It takes at least a 10X magnification to be able to correctly identify them.

The adult mite's cuticle (covering) has simple striations that can be seen from both the dorsal (top) view and from the ventral (bottom) view. The ventral view of the house dust mite reveals long setae (hairs) extending from the outer margins of the body and shorter setae on the rest of the body. Through the 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 the body (resembles head) and a tough, translucent shell, giving a "fearsome appearance."

BIOLOGY AND LIFE CYCLE

Adult females lay up to 40 to 80 eggs singly or in small groups of three to five. After eggs hatch, a six-legged larva emerges. After the first molt, an eight-legged nymph appears. After two nymphal stages occur, an eight-legged adult emerges. The life cycle from egg to adult is about one month with the adult living an additional one to three months.

The diet is varied with the primary food source, consisting of dander (skin scales) from humans and animals. However, needed nutrients can be provided from fish food flakes, pet food, fungi, cereals, crumbs, etc. Many mite species live in bird's nests, in barns, among stored grain, straw, etc.

House dust mites are cosmopolitan in distribution with much of the research previously done in Europe.

One of the major limiting factors in mite survival and population development is the availability of water for sorption. Highest mite densities occur in the humid summer months and lowest in drier winter periods. Dust mite populations are highest in humid regions and lowest in areas of high altitude and/or dry climates.

Due to the large quantity of skin scales sloughed off daily by humans, mites have an abundant food supply. Dust mite antigen levels are measured in bed dust, floor dust, and room air samples. Detection in room air was best during cleaning and bed-making activities.

DETECTION

House dust mite presence is often suspected before they are actually seen and accurately identified. Requests for control often come from individuals who have been diagnosed by medical personnel as allergic to the house dust mite or the allergens produced.

The presence of house dust mites can be confirmed microscopically which requires collecting samples from mattresses, couches or carpets. Also, it requires the use of a microscope with sufficient magnification and the technical ability to recognize house dust mites under the microscope. In general practice, testing is unnecessary.  dustmites are extremely common in household environments. They virtually always show up in a test, so testing just adds expense.  A better question than "are dust mites present?" is "How can I control or remove them?"

WHAT CAN WE DO?

A number of researchers have studied dust mites control and have a set of reccomendations that are proven to be effective. Reccomendation focus on "dust control"

One must reduce the concentration of dust borne allergens in the livin environment by controlling both allergen production and the dust which serves to transport it.

For the bedroom environment you will want to use some or all the following methods. We have listed them in order of practicality combined with effectiveness:

  1. The most effective means is to enclose the mattress top and sides with mattress protector. Thoroughly vacuuming mattress pillows and the base of the bed. Put an airtight plastic or polyurethane cover over your mattress. This is the method recommended by Consumer Reports. This tip is number one for a reason: it is in your bed (including the baby's crib) that you are closest to the mites and their feces and enclosing the mattress and pillows in a dust mite cover virtually eliminates the mites here.  Mattresses covered with "fitted sheets" help prevent the accumulation of human skin scales on the surface.  These sheets have the advantage of being waterproof, too, which helps protect your mattress from spills, babies and toddler's waste, too.
  2. Wash your sheets, pillows and blankets in very hot water.  Wash the sheets and blankets at least every two weeks. Wash your pillow every week or put a dust mite-proof cover on it and wash once per year. Your pillowcase goes over the dust mite cover.  How hot is hot? The water used to wash your sheets and blankets should be at least 130°F (54°C). Set your washing machine to it's hottest setting.  If the water doesn't seem to be coming out hot, you may want to check your hot water heater - you may not realize that most household hot water heaters have a knob that can adjust the temperature of the water it produces. For fabrics that may not be washed in hot water; just pop it into the freezer for 24 to 48 hours to kill dust mites. And for those who travel and stay in hotels (or with less hygienic friends and family): 

  1. Use Synthetic fabrics: Replace feather and down pillows with those having synthetic fillings. Replace woolen blankets with nylon or cotton cellulose ones. And don't forget the children's stuffed animals: be sure to get washable stuffed animals in the future! Memory foam mattress manufacturers claim that their mattresses create an environment that is unfavorable to dust mites.  Even so, an encasement is still advised, also because it can stop bedbugs (which are a rapidly growing problem)
  2. Reduce temperature and humidity: Dust mites love warm, humid conditions, above 70 F (21 C) and 50% or greater humidity. 
    Temperature: Keep the thermostat in the house below 70 degrees.
    Humidity: Effective control of mites would require the maintenance of relative humidity's below 50 percent. Here is a range of dehumidifiers from a large basement or ground floor model, to a small room model.  The big ones are pricey, but they last for many, many years. (we have one in the office that is 20 years old!) A study (Feb 2005) by Kingston University (London UK) shows that simply by leaving your bed unmade each morning, with the sheets to be exposed to the air, allows the sheets to dry out, and substantially reduces the numbers of dust mites. Now, you have a legitimate reason not to make your bed!
    Some researchers feel it is important to focus on decreasing indoor humidity, especially during the winter period to reduce dust mite populations. One might forsake humidifier use during winter periods (or limit it to the bedroom only at night, then ventilate the room during the day). It will help to use dehumidifiers during high-humidity periods, or use central air conditioning. So if you use a humidifier in the winter, adjust it to produce 35% to 45% humidity.  Some humidifiers have  this control built in; with others, you'll need a humidity gauge (usually sold with a thermometer at Costco, Sam's Club, Wal-Mart, Target, etc.). And generally, homes that have their air conditioners on constantly in the summer and dry heat in the winter have lower mite counts than non-air conditioned homes.
  3. Clean weekly: Weekly change pillowcases, sheets, and under blankets, and vacuum the bed base and around the covered mattress.   Clean flooring: Use a damp mop or rag to remove dust. Never use a dry cloth or broom, since this just stirs up mite allergens.
  4. Clean daily: Daily damp dust the plastic mattress cover.
  5. Frequently wash all bedding (blankets, mattress pads and comforters) in hot water (130 degrees F [or 60°C] weekly). Cold and warm water won't kill mites. Also wash curtains.
  6. Steam clean surfaces and materials that cannot put put through the washing machine: Using pure steam dissolves dirt and grime, while removing germs and bacteria from the surfaces that you're cleaning. Steam is also an economical and environmentally friendly thing to do. There is no longer the need to use harsh and toxic chemicals. It is also a great way to kill dust mites and bed bugs. 
  7. Remove carpeting and install wood, tile, linoleum, or vinyl floor covering. Remove cloth drapes and blinds. (If you have carpet, vacuum every day.) Vacuuming your carpets and upholstery every week can help. See the caution about vacuuming below under tips. Vacuums with high-efficiency filters pick up more dust mites, but even standard vacuums work well enough. 
  8. Freezing and sunlight kills mites but does not remove their residue.  In addition to freezing temperatures and washing items in temperatures greater than 130 degrees F, extended exposure to sunlight, and low levels of humidity also destroy the mites.
  9. Children's soft cloth toys: Regularly place soft toys in the freezer for 24 hours before you wash them, or wash them in hot water. Removing them, or at least reducing the numbers of them on the beds, will help, too.
  10. Air Purifiers: While it is better to stop the dust mites at the source, reducing the dust levels in the air is a good secondary measure. Some pest control firms sell air purifiers to eliminate the food source of house dust mites. Although ozone air purifiers emit a low level of ozone (activated oxygen) that attaches to fungus, mold, and bacteria on skin flakes, EHSO does not recommend ozone generators (neither does the US Food and Drug Administration).  The same ozone that is oxidizes the dust mites is bad for your health. Air purifiers that use HEPA filtration are more effective and safe to use.  Various types of air purifiers can be attached to the central air return to decrease irritants. Most filters remove 50 to 70 percent of material. HEPA filters will remove up to 99 percent of the material; not just dust mite feces, but also all types of other allergens, like animal dander, dust, pollen, cockroach feces, etc... 
  11. Furnace Air Filters: Clean or replace the air filters on your furnace or air conditioner at least once a month. Filters that are rated to trap allergens are obviously more effective than plain spun glass.

Services to Kill Dust Mites and Clean Mattresses?

There are companies offering a service, using steam or ultraviolet light, to kill dust mites in mattresses and remove them. The Wall Street Journal (January 5, 2010, Page D2) had an article by Laura Johnnes titled "Does Mattress Cleaning Treat Dust-Mite Allergies?" Their conclusion, including that of Dr. Peyton Eggleston, a pediatric allergist and professor at Johns Hopkins Children's Hospital in Baltimore, was that there isn't any scientific research or evidence to back up the service companies claims, and that the dust mites would probably return to previous levels within a month or two.  This substantiates the approaches above, including encasements (see number 1, above).  A cleaning might make sense if the mattress is fairly new (1 to 3 years) and you encase it after the cleaning.