ALLERGY: WHAT ARE HOUSE DUST MITES? WHERE ARE THEY FOUND?

Certain environments do not favour house dust mites. They are killed by sunlight. The majority of mites live in the top 1-2 cm (% inch) of any surface, and sunlight can penetrate far enough to kill by light or drying many of the mites present, although it does not remove their faeces or debris. Washing at high temperatures (90oC/194°F plus) also kills mites, and, if thorough, can remove them and their faecal debris completely. A dry environment kills them. They do not survive at a relative humidity level below 55 per cent, and if you can create localised dry conditions, say by drying a pillow on a radiator or hot water tank, or by drying a bed with hot water bottles, or with an electric blanket, this will kill them, although again faeces and debris are not removed. House dust mites do not occur in any concentration in the Alps; the combination of low humidity and low temperatures is probably the reason for this.

Synthetic materials are often claimed to deter house dust mites and advice is often given to use synthetic bedding, to avoid problems with house dust mite allergy. Despite the prevalence of this advice, there is little evidence to substantiate it, and the experience of many people with allergies indicates the need for caution.

Problems with mites can, and do, recur in synthetic bedding after a while, unless you take preventative measures to deter them (so the benefits can be due simply to the newness of the bedding, not to the change to synthetic material).

There is some evidence that synthetic carpets can reduce the level of airborne allergens (including house dust mites) because their increased level of static electricity attracts particles and holds them down. There are also some benefits to using synthetic bedding, compared to wool or feathers, in that it can be readily washed and dried. However, washing at low temperatures (40°C/105°F or less) does not kill mites. It simply rinses out the faecal pellets, but not always the mites themselves, who are tenacious and cling on to survive. You need a high temperature of wash to kill and eliminate mites.

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