House dust mite allergy and anti‐mite measures in the indoor environment

House dust mites occur in many Danish dwellings, but the majority of the residences do not contain a mite population (1). This uneven distribution shows that it is possible to have dwellings free of mites. Effective prevention must therefore involve a change in environmental factors that separates houses with elevated mite counts from "normal" dwellings. Considering which factors determine the numbers of mite counts in dwellings, it has been shown that it is not nutritional limitation that determines the number of mite counts, but the humidity in the houses (2). Abnormally high mite counts are found in dwellings with air humidity above 7 g/kg air during the dry winter months (3). Changes in environmental conditions by moving people with asthma and house dust mite allergy to an environment free of house dust mites result in an improvement of their clinical condition (4,5). This shows that it is a relevant approach in the treatment of house dust mite asthma to try to reduce exposure to house dust mites (secondary prevention). Furthermore, a reduction in population exposure to house dust mites most likely will result in a decreased incidence of allergy to house dust mites (primary prevention) (6).