High altitude and house-dust mites.

House dust from high mountainous areas of Switzerland contains very few house-dust mites. In contrast to lower-lying regions, only very small quantities of house-dust allergen are found at high altitudes.The cause of this phenomenon seems likely to be the climatic conditions in the high mountains of Europe, where cold air leads to extremely low humidity levels indoors. The soil conditions and a type of construction providing good protection against the penetration of water also contribute to dry conditions in houses. These factors prevent the development of large populations of allergen-producing house-dust mites.The beneficial effect of a stay at high altitudes on patients with atopic asthma is probably due to the low concentrations of house-dust allergen.