It is not the mite itself which causes the allergy symptoms, but its excrement instead.
Mites are tiny, spider-like animals, which are not visible to the naked eye. They can be found all over the world; only areas which are situated more than 5,000 ft. above sea level are virtually mite-free. Thus, house-dust-mites are not an indicator of a lack of cleanliness!
Mites thrive at constant temperatures of about 25 oC (77 oF) and at a relative humidity of around 70 percent. Therefore, the warm bed climate makes for particularly favourable living conditions for mites. The human body provides warmth and the necessary humidity via perspiration throughout the night.
Moreover, there is plenty of food: house-dust-mites live on the scales of human skin. Every human being loses up to 1 gram of skin scales per day, which is enough to feed thousands of mites.
It is the substances contained in the mite excrement which actually trigger the allergy. It brings about symptoms such as coughing, cold or watering eyes. These ailments occur especially during the night and in the morning.
Roughly from May on, when the air becomes more humid and temperatures rise, the mites start to proliferate heavily. House-dust-mite population numbers peak during the fall. The dropping temperatures at the beginning of winter and the drier air as a result of the indoor heating, cause many mites to die. Their faeces, however, have accumulated during the summer and are then circulated within the apartments and houses by the warm air from the heating. This is the reason why house-dust-mite allergy sufferers show increased symptoms particularly in the fall and winter.
Mites belong to the class of arachnids or spider-like animals. The house-dust-mites (pyroglyphidae) grow up to ca. 0.1 to 0.5 mm in size. Of the four different species that can be found all over the world, dermatophaoides pteronyssimus is the most relevant for allergy sufferers.
This house-dust-mite produces the allergen which is called “Der p1“. The process involves a kind of symbiosis the mite forms with certain species of fungi and bacteria. House-dust-mites are not capable of directly using the fatty scales of the human skin on which they feed. The skin scales must first of all be “pre-digested“ by the bacteria. Only then can they be ingested by the mites. Bacteria inside the mites’ intestines further digest the scales. The by-products, which remain at the end of this digestive process, are the allergenic protein components. By friction, the allergy-causing mite excrement splits into very small particles, which may mix with the house dust and enter the respiratory system.
House-dust-mites are the second most frequent trigger of allergic diseases of the respiratory tract (at 38.3 percent after pollen at 85.9 percent) in Germany.
K. C. Bergmann/G. Albrecht/P. Fischer: Atemwegsallergiker in Deutschland. Ergebnisse der Studie Allergy Living & Learning. Allergologie 2002; 3: 137-146
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Verband der Deutschen Daunen- und Federnindustrie e.V.
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