Mite sensitization in the Scandinavian countries and factors influencing exposure levels

Mites are the common sources of indoor allergen and play a major role in se nsitization and elicitation of allergic disease. In the Scandinavian countr ies, mite infestations in the home were not common in the past decades. Rec ent studies show that sensitization to mites among children, particularly i n Sweden, is increasing. Similar trends have also been reported in Norway. Poor indoor climate, e.g., high humidity and poor ventilation as a conseque nce of energy-saving measures, are cited as a possible explanation of this increase. Modern furnishings, e.g., carpets and various kinds of upholstery , may also serve as reservoirs of indoor allergens. At least 2 mu g of mite allergen per g of dust is considered to be a risk level for sensitization and symptoms of asthma. As compared to experience from other parts of the w orld, mite-allergen levels are generally low in the northern Scandinavian r egions. Recent studies from Sweden and other European countries show that m ite sensitization may occur below 2 mu g/g dust. Various environmental adju vant factors may affect the threshold levels of allergen. In this review, t he importance of the indoor environment for the accumulation of mite allerg ens, sensitization to mites in the Scandinavian countries, and various envi ronmental factors that could influence exposure levels will be discussed.