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House dust mites and asthma

House dust mites can trigger allergic reactions such as asthma, eczema and rhinitis (runny nose). Cutting down mite numbers may reduce these reactions. The information below aims to give advice on how to reduce mite numbers in the home.

What are house dust mites?

House dust mites are creatures which are so small they cannot be seen with the naked eye. They live in all our homes and feed mainly on the scales of the skin that we shed. They are most common in warm, damp, dark areas where dust containing skin scales gathers. These areas include pillows, mattresses, carpets, soft furnishings, soft toys and even clothing.

The mites are harmless to most of us, but they can cause allergic symptoms in some people. These symptoms are caused by breathing in substances known as allergens which are contained within the mites' droppings. The droppings are tiny, dry pellets which forms a large part of the dust in areas where mites are found. The pellets are so small that they can become airborne, and may then be breathed in. There are other allergens, as well as that from the house dust mite, which can trigger allergic reactions. These allergens can be produced, for example, by moulds, cats and dogs, or pollen from trees and grasses.

Why do they need to be controlled?

The number of people with allergic asthma and similar illnesses is rising around the world. In this country, about two and a half million adults suffer from asthma and one child in seven is affected. House dust mite allergen is one of the most common triggers of asthma. About one in ten of us has a family tendency to develop allergic asthma if we are regularly exposed to high levels of allergens. Controlling the levels of allergen could stop people with a family tendency for allergic asthma from developing the disease. This is particularly important for very young children.

If you have allergic asthma it is quite likely that you are allergic to house dust mites. Skin tests can help to identify allergies but they may not show you everything that could be causing your asthma. If you think that you or your family may be allergic to house dust mites try taking the first steps in the following guide to see whether there is any improvement. If you are in doubt you should consult your Doctor.

You cannot get rid of all the mites from your home. But you can cut down the numbers a lot. For best results the steps should be carried out over the whole house. Many of the steps apply to the bedroom because this is likely to be where the most time is spent. It may take at least two months before the effects of carrying out the steps are noticed. If possible carry out steps 1 and 2 to start with then see if there has been any relief of allergic symptoms before moving on to later steps.

Step 1 - reduce the dampness in your home

House dust mites prefer warm, damp homes. Dampness should lead to the growth of moulds, which can cause allergic reactions too. These are some ways to avoid dampness:

• open windows or vents in kitchens and bathrooms during and after cooking, washing and bathing and to stop dampness spreading to the rest of the house, keep the door to these rooms closed
• avoid drying clothes indoors, especially in the bedroom and living room, unless using driers which are vented outdoors and if you have to dry clothes indoors, open a window and close the door to the room where the damp clothes are
• leave the bed open to air before remaking beds
• open windows or vents in bedrooms

Step 2 - prevent the build up of dust

Removing dust is important in the homes of allergy sufferers and to help prevent dust building up in the home try the following.

• Reduce the number of items on which the dust can build-up, especially if they are difficult to clean. You can do this where possible by keeping ornaments in display cabinets, placing books in closed cases, and putting clothes and other objects in cupboards or drawers.
• Regularly clean surfaces/objects where dust collects using a damp cloth (dry cloth will not pick up all the dust and will let a lot of it back into the air).
• Regularly wipe down window blinds with a damp cloth.
• Vacuum clean soft furnishings and curtains as well as carpets/floors.
• Replace the air filter or dust bag in the vacuum cleaner regularly.
• Vacuum clean mattresses every two weeks.

Step 3 - high temperature washing

Washing fabrics at a minimum of 60^oC kills dust mites so use sheets, pillow cases and duvet covers that can be washed at 60^oC and wash them at this temperature at least every two weeks. Use curtains that can be washed at 60^oC and wash regularly at this temperature.

Step 4 - bedding and soft toys

House dust mites are found in large numbers of mattresses and pillows where there are lots of skin scales. To reduce the number of mites in these areas:

• regularly wash pillows at 60^oC or replace with new ones every six months
• replace blankets with duvets which are made of synthetic material
• cover all mattresses, duvets and pillows in the sufferer's bedroom with micro-porous membrane covers, these covers need to be wiped clean with a damp cloth each time the bedding is changed

Stuffed toys can also contain house dust mites so try to reduce the allergy sufferer's contact with these toys. Keep the toys away from the bed if possible. Otherwise, about once a month put soft toys in the freezer for 6 hours to kill the house dust mites and then wash to remove the remaining allergen

Step 5 - carpets

Carpets also contain a lot of house dust mites. Replacing carpets can be expensive but if you are going to change your carpet anyway these are some options which will reduce the number of mites present.

• Replace carpets with linoleum / vinyl flooring or sealed natural flooring such as cork tiles or wood and make sure that the new floor does not have cracks in which dust may build up.
• Choose very short pile synthetic carpets as they tend to hold fewer mites than long piled wool carpets.
• Use cotton rugs that can be washed at high temperatures and wash them regularly.

Step 6 - high efficiency filter vacuum cleaners

There are vacuum cleaners on the market which are better at collecting dust than ordinary vacuums, so consider buying a high efficiency filtered vacuum cleaner and use regularly on floors, carpets, soft toys and soft furnishings.

Step 7 - treatment of furnishings

Every three to six months treat carpets and soft furnishings with either of the following to kill mites.

• Acaricides/antigen denaturing compounds, though for your own health and safety it is very important that the instructions for use and disposal shown on the package label are followed carefully.
• Liquid nitrogen, which should only be applied by a specialist contractor.

Step 8 - replace furnishings

When you buy new furnishings you should consider replacing woven-fabric covered chairs and sofas with cane, canvas, leather-like or leather-covered furnishings which are easy to clean and do not harbour house dust mites.

Other possible measures

Products such as air filters, ionisers, dehumidifiers and mechanical devices for ventilation with heat recovery are available. These may also help to reduce allergic symptoms, but their effectiveness has not been fully tested as yet.