House dust mites are small arachnids, members of the family Pyroglyphidae, measuring 0.2–0.4 mm in length. The most common and abundant house dust mites are Dermatophagoides pteronyssinus ja Dermatophagoides farinae, which account for 80–90% of the mite population in a domestic environment. Indoor relative humidity of 50% or higher is the key factor that determines the survival and development of the house dust mite population. Niches for these mites are formed of textile materials such as beds, carpets, upholstered furniture, soft toys, and clothing. House dust mites are natural inhabitants of our surrounding environment. However, constant exposure to house dust mites may lead to sensitization to mite allergens. In Estonia, the prevalence of sensitization to house dust mites is up to 14% among adults and up to 9% among schoolchildren. The most common diseases related to house dust mite allergy are asthma and allergic rhinitis. Sensitization to house dust mites is a major independent risk factor for asthma and allergic rhinitis in areas where the climate is favourable for growth of the mite population. Sensitized individuals are likely to have more severe asthma when exposed to high dust mite levels.
Specific prevention and treatment of house dust mite allergy are based on avoidance of house dust mites and on specific immune therapy. Several methods have been recommended for reducing exposure to the house dust mite allergen. These methods include mite-impermeable encasing covers for mattresses and bedding, hot washing of bed linen, hot washing or freezing of soft toys, use of acaricides, removing carpets, minimising upholstered furniture, use of vacuum cleaners with a HEPA filter, and reducing relative humidity. However, the success of mite allergen avoidance programmes appears to be limited and depends on the stage of the disease.