It is well recognised that the filter like properties of carpets hold dust including allergen, and as previously discussed, it carries out the important function of holding and preventing it from circulating in the air. Most importantly it holds the dust until it is removed, by regular and efficient vacuum cleaning and periodic carpet cleaning , typical of a regime in a well maintained home in the UK.

The real key to controlling dust mite populations is to control the temperature and relative humidity indoors to prevent the warm, humid conditions that dust mites need to live. The easiest way to achieve this is to ensure good ventilation in the home, particularly in bedrooms, which is the critical zone, and also avoid excessive temperatures.

Cleaning of carpets

The accumulation of dust mite allergen in carpet depends upon the balance between its production and its removal. Production of allergen is very slow and it takes a considerable period for a significant allergen build-up to occur. Although allergen is a very stable compound some is removed from carpet by natural biological or chemical breakdown, most remains until removed by cleaning through normal vacuum cleaning.

The very fine allergen particles and minute flakes of skin, which comprise the food source of the mite, are easily removed from carpet by a proper cleaning regime. A carpet cleaned regularly, in a well-ventilated environment, will not contain enough allergen to affect most people. The vacuum cleaner will ideally have a powerful suction and, have efficient filtration to ensure the retention of the allergen within the cleaner and preventing its release into the air. The British Allergy Foundation has an evaluation and accreditation scheme for vacuum cleaners and asthma sufferers are recommended to use a machine approved by them.

The physical action of vacuum cleaning will probably provide sufficient agitation of the carpet surface to allow allergen particles to be stirred up into the atmosphere. The action of opening windows during and, for a period after, vacuum cleaning will ventilate the room and effectively remove the allergen from the air.

One additional benefit of regular vacuum cleaning is the removal of skin flakes from the surface of the carpet before they condition (i.e. absorb moisture) to the point that they become edible for the dust mite. This reduction in available food supply will reduce mite populations.

Studies involving 13 classrooms in the U.S.A. showed that a single dry extraction carpet cleaning operation reduced the average level of dust mite allergen in carpet dust by 51%. (16) A further study involving 57 homes in Georgia and Wisconsin showed that a single dry extraction cleaning operation reduced the average level of cat allergen (Fel d 1) by over 85%.

Occasional wet extraction cleaning of the carpet is also to be recommended to reduce deep seated dusts and steam cleaning has also been found to be particularly efficient at removing a high proportion of allergen and completely killing the dust mite population.

Summary

When a household is ventilated and vacuum cleaning of a normal frequency and intensity is carried out, carpet in UK homes:
- Will not hold sufficient food for dust mites to survive,
- Will contain minimal allergen loads on the surface waiting to become airborne.
- Will not provide an indoor environment for dust mites to live.