Dust Mites

The dust mite serves as nature's cleaner and has existed for millions of years. Dust mites are related to the arachnid family that includes spiders, ticks, and chiggers. They have eight hairy legs, no antennae, no eyes, no organised breathing system, and a mouthpart on the front of the body. Dust mites have sticky pads on the ends of their feet making it easy for them to burrow deep into carpet and furniture. This is one of the reasons why only dead dust mites are typically removed by vacuuming the carpet. Dust mites can be found in your house, regardless of how clean you keep it. The humidity, the temperature, and the amount of furnishings in a home will help determine their population numbers.

The two main species of house dust mite (Pyroglyphidae) found in homes belong to the genus Dermatophagodies. They are the North American House Dust Mite (Dermatophagodies farinae) and the European Dust Mite (Dermatophagodies pteronyssinus). These two types of dust mite account for around 90% of the mite population found in houses.

Dust mites are tiny, translucent, and are not visible to the naked eye. A dust mite can grow to about 0.3mm size or 300 microns in length. You would require a significant degree of magnification to be able to see one, at least ten times normal. A single gram of house dust, about half a teaspoon or the weight of a paper clip, can contain as many as 19,000 dust mites. This includes 250,000 of their own faecal droppings, which dust mites can eat in order to gain nourishment. Although they are totally blind, dust mites can discern whether what they encounter is food or waste lacking nutritional value.

Dust mites pass through six developmental stages and once in the adult form they moult once, creating skin casts. Every three weeks an adult female lays between 40 to 80 sticky-coated, cream-coloured elliptical eggs, either singly or in small clusters of around five. The transition from egg to an adult dust mite usually takes about one month. Once the eggs hatch, a six-legged larva emerges. After the first moult, an eight-legged protonymph appears and this is followed by a tritonymph stage. The dust mite then becomes an adult, which will live anywhere from one to three months. Because of overlap, all the life stages can be found in any one season.

Dust mites are not parasites that live on a living host like some other types of mites. Dust mites do not bite humans because they are scavengers and feed on the dead and mouldy skin cells that drop from our bodies or from that of our pets. The body warmth of humans and the skin flakes they shed are conducive to dust mite growth and survival. Dead skin cells make up to 80% of household dust and about 80% of the material observed floating in a sunbeam is actually skin flakes This dead material is commonly referred to a "dander". Human beings shed approximately 6 grams, or a 5th of an ounce, of dead skin every week. Dust mites will consume almost anything, including pollen granules, insect scales, fungi, lepidopteran (butterfly and moth scales) bacteria, pieces of dead mites, and dried semen.

After the particles of food have been digested by dust mites, they become enveloped in the mite's digestive proteins. These enzymes extract all the nutrients from the food before it is discarded as faecal pellets. Dust mites leave their droppings wherever they go and this is an important factor in causing reactions in people with asthma and other allergic conditions. These droppings contain proteins, specifically DER p1, which are residual enzymes from the dust mite's gut that are used to digest the flakes of dead skin. Dust mite's microscopic casts and their droppings are believed to be a main cause of asthma worldwide. An individual's perennial allergic rhinitis or asthma can be triggered by these allergens.

Dust mites are present in every house to varying degrees but they thrive in a dusty environment with adequate moisture. They are less common in very cold climates or at altitude. Dust mites do not drink water. Instead, they absorb water through the air and their environment. They obtain water via a system of hydrophilic crystals in their bodies and this helps to protect them against dehydration when conditions are dry. This is important because the dust mite itself is composed of about 80% water. The fibrous structure of textiles enables dust mites to cluster and reduces water loss. Humans provide water vapour through perspiring and breathing, and they are able to produce approximately one pint per person per night.

The more humid their environment, the more food the dust mites will consume. Ideally, they prefer an environment with humidity of about 80% and a temperature in the high twenties in degrees Celsius, or about 80 degrees Fahrenheit. They do not survive well in more extreme temperatures with lower humidity. In fact, they cannot survive if the humidity is below 50%.

The highest mite densities occur in the humid summer months and are lowest in drier winter months. In the United States, the allergen levels for dust mites remain high throughout the year, although they do peak in July and August. In New Zealand, dust mite numbers peak in March and April. September and October have the lowest allergen levels but the cold weather may not alleviate the allergy because dust mite faecal particles, skin casts, and disintegrating dust mite bodies often remain.

Dust mite allergies are usually characterised by perennial allergic rhinitis, which occurs all-year round. The common symptoms of this condition include a runny, itchy, or stuffy nose, sneezing, and red, irritated eyes. Although dust mite allergies are often perennial, the symptoms may abate slightly during the summer because more time is spent outdoors and heaters are not used. Symptoms often worsen when the dust is circulated in the air by movement or cleaning. Diagnosing a dust mite allergy typically involves discussing the history of symptoms with a doctor or allergy specialist as well as skin-based allergy tests.

Asthma and eczema can also be triggered by dust mite allergy. People with asthma may find that exposure to dust mites and dust mite debris provokes wheezing and other symptoms. It has been estimated that dust mites may be a factor in 50% to 80% of asthmatics, as well as having a role to play in many cases of eczema, hayfever, and other allergic complaints.

Dust mites like warm, humid areas filled with dust, especially carpets, furniture, mattresses, pillows and bedding. The bedroom and other lounging areas often harbour large numbers of mites. To give you an idea of how many dust mites may be present in your bed, a typical mattress can contain anywhere from 100,000 to 10 million mites. The average number is about 2 million dust mites per bed. Each dust mite produces about 20 dropping daily so it has been estimated that around 10% of the weight of a pillow that is two years old is composed of dead dust mites and their faeces. Dust mite antigen levels are highest in bed and floor dust, and in the air during cleaning and bed-making activities. As people toss and turn during the night they can easily propel dust mite droppings into the air. Once in the air, these allergens can stay there for up to two hours and are easily inhaled into our airways.

Tips for controlling dust mite allergies

If possible, avoid contact with dust mites and their faeces. Remember that while it is unlikely that dust mites can ever be completely eradicated from the home, you can take steps to reduce the dust mite population.
Take an antihistamine to reduce allergy symptoms.
Have a shower or bath before going to bed to remove dead skin particles.
Dust mites cannot survive on vinyl, tile, or hardwood floors where dust does not accumulate. These surfaces are best used in the bedroom of a person sensitive to dust mites.
No matter how you vacuum or dust, it is very difficult to reduce the number of live dust mites present in carpeting and mattresses. Old mattresses can easily carry up to a million live dust mites.
Special dust mite or allergen proofing covers on bedding can be effective at keeping the dust mites inside the mattress and restricting their supply of food. These covers usually involve encasing bedding in impermeable rubber, vinyl plastic or other vapour-permeable material. Bedding should be washed weekly using hot, soapy water. It is a good idea to keep animals out of the bedroom if possible.
Reducing the level of warmth and humidity will discourage dust mites. A dehumidifier and an air conditioner can also help, provided that they are cleaned regularly. Dust mites need a relative air humidity above 60% to stay active and they thrive in environments that offer a relative humidity of 80% all year round.
Dust mites are susceptible to extremes in temperature. Sustained heat or boiling water at temperatures above 60 degrees Celsius can be effective at killing the mites and their eggs. Heat can be provided by tumble-drying washing, placing clothing in direct sunlight, or by dry heating with electric blankets. Hot water at a temperature of around 130 degrees Celsius will kill all mites.
Cold water will remove about 90% of mites. Freezing temperatures can damage the mite's hydrophilic crystals, making them more prone to dehydration. For example, soft toys can be frozen in a freezer and then put in a dryer for 30 minutes or put in sunlight for about six hours.
Dry cleaning will kill all the mites and is also very effective at physically removing dust.
Clothing is also a possible source of dust mite allergens and needs to be washed in very hot water and dried thoroughly.
Get carpets cleaned professionally with superheated steam to kill living dust mites. Fixed carpets with thick underlay are particularly difficult to clean and loose pile carpets allow for the accumulation of food and moisture, creating a microhabitat that suits the mites.
Powerful high filtration vacuum cleaners can be used on curtains, carpet, mattresses, and upholstered furniture to remove non-living dust mite allergens from your home. Do not use wall-to-wall carpeting. It also helps if the vacuum cleaner has a fine exhaust filter that prevents the particles from merely being redistributed elsewhere.
Avoid anything that collects dust, including fabric wall hangings such as pennants or tapestries, books on shelves, etc.
Wood, vinyl or leather furniture will be more resistant to dust and, therefore, dust mites. Dust mites do not live in air ducts.
Use plastic shades or washable curtains in preference to heavy drapes, blinds or curtains.

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