Dust Mites

House dust is a mixture of various waste materials like dead human skin cells, animal dander, fabric fibres, dust mites, bacteria, cockroach parts, mould spores, food particles and other debris.

In fact, dead skin cells account for up to 80% of house dust. However, it is the the house dust mite allergen that is the most common contributor to allergic asthma, allergic rhinitis and atopic eczema.

So generally, when doctors say that patients are allergic to house dust, they usually refer to the house dust mite. Of course, patients could also be allergic to other elements of house dust, such as cockroach parts, mould, animal dander and so on.

back to top 

What are Dust Mites?

Dust mites are eight-legged insects that belong to the spider and tick family (i.e. Arachnid family). At up to 0.3 mm length, they are barely visible without a microscope. They belong to the genus Dermatophagoides, which means "skin eater".

It is so named because it feeds on animal materials with high protein content, especially dead human skin cells. It also feeds on mould. The two common species throughout the world that are also allergenic are the Dermatophagoides pteronyssinus (Der p), and Dermatophagoides farinae (Der f). In the context of tropical environments like Singapore, there is a third species called blomia Tropicanis.

The female dust mite lays up to 50 eggs within 3 weeks, and each egg takes about three to four weeks to reach adulthood. The lifespan of a dust mite is about 10 weeks, and each female would have laid between 40 to 80 eggs within a period of about 6 weeks. So, it is easy to see that they multiply at a very fast rate indeed, especially if the conditions are right (see below).

back to top 

What is dust mite allergen?

The common misconception is that the dust mite itself is the allergen that causes the allergic reaction. Actually, it is the fecal dropping of the dust mites, as well as their broken-up exoskeletons which contain the offending antigen. This allergenic material is actually an enzyme that is used to digest their food.

A dust mite can produce 20 fecal droppings per day, 200 times their body weight in their short lifetime. Some estimate that 10% of a two-year-old pillow's weight can be made up of dust mites and their droppings.

A gram of dust can contain as many as 1,000 dust mites. This same gram can contain 250,000 fecal pellets that are much smaller and lighter than dust mites, and can be easily breathed in.

Research indicates that most people toss and turn up to 70 times during one night's sleep. Every time the mattress is moved, the tiny allergens are expelled into the air, and are easily inhaled.

back to top 

Where do dust mites live?

Dust mites thrive best where the relative humidity is above 70% RH, and temperatures above 23^oC. As such, tropical climates like Singapore would have a higher dust mite population than temperate climates in Europe or North America. Conversely, dust mites are rare in cold climates, or during winters.

Within the home, the most of the dust mite colonies can be found in the bed mattress, pillows and bolsters. This is because these areas have high concentrations of:

• food - we shed a lot of skin cells throughout the day,
• humidity - we perspire when we sleep, and there is vapour in our breath,
• warmth - our body heat.

Other areas which are particularly susceptible to dust mites are the carpet or rug, soft toys, upholstery and anything else that can trap dust - e.g. curtains and clothes.

Dust mites can be found in all homes, despite best efforts to keep them clean.

back to top 

Can dust control measures help?

The logic is simple - if dust mite allergen is a major cause of allergic symptoms, then the avoidance of the allergen will reduce the symptoms. This has been proven in many peer-reviewed published research, and has been the experience of many patients worldwide, including Singapore.

Patients usually experience immediate relief associated with lower levels of allergen exposure. Some studies indicate that after about eight months of prolonged avoidance, it appears that the patient's threshold for allergic reaction is raised - i.e. it would take more allergen than before to cause a reaction, thus there appears to be a more permanent improvement.

This is contrary to the popular misconception that more exposure will improve our immunity - this works with germs, but simply does not work when a person already has the allergies - the opposite is true in this case.

Every day that an allergic individual can avoid contact with the allergen, his cells (lungs, nasal, skin etc.) will have a chance to rebuild themselves. The analogy is like a fort that is constantly under bombardment. A long "safe" or "quiet" period is necessary to recuperate and shore up the defences. That is why if an allergic asthmatic has asthma today, his chances of having an attack tomorrow goes up, and vice versa.

See the medical sections for allergen avoidance research.

back to top 

What are the dust control measures that can be taken?

In general, one should focus on three areas:

• bed - encase the mattress, pillows and bolsters with mite-proof encasings. Use synthetics where possible as mites grow best in natural fibres like wool and down. Wash all bedding, including blankets, in hot water (mites only die at about 60^oC). If that is not possible, then add anti-mite additive to the wash.
• air - use medical-grade True HEPA air cleaners for removing fine airborne allergen. Be careful to use one that is powerful enough for the room - because an underpowered air cleaner will not be of much use as it cannot remove the airborne contaminants faster than they go airborne.
• floor & others - remove carpets & rugs, or use anti-mite spray; this also includes area like sofas, curtains, soft toys, clothes etc can be treated with anti-mite solutions. Vacuuming with normal or water-based vacuums should be avoided as this stirs dust up into the air. Instead, use a medical-grade True HEPA vacuum with industrial-strength suction. High suction is necessary because dust mites have suction pads and hooks in their legs, which they use to cling stubbornly on to their host.

Each of these three areas are important sources of dust mites - only taking care of one or two areas is not enough, as the total allergen in the environment is still high. While it is impossible to keep the allergen down to zero, we have to keep them to the minimum, below the patient's threshold that trigger allergic reactions.

These equipment make good investments, because in the long run, they are cheaper than numerous visits to the doctor. More importantly, the patient's condition will improve. The only caveat is if the patient is also allergic to other things e.g. allergic to food, he has to control his diet as well. If not, his allergic reactions may decrease insofar as mites are avoided, but he will still have attacks due to the other allergies.

back to top