The term "house dust allergy" is basically not entirely correct, because the natural outgrowths of the allergy are not in the house-dust itself. Ordinary house dust consists of large pieces, skinning, textile fibers, feathers, fungi, bacteria, algae, house dust mites, pollen and food remnants. The trigger of the allergic symptoms of a house-dust allergy are certain proteins, which are found mainly in the feces, but also in the body of dust mites.
Dust mites are among the arachnids, mostly the species Dermatophagoides pteronyssinus, Dermatophagoides farinae or Dermatophagoides microceras. The genus name, Dermatophagoides, has its origin in the Greek language and means translated "skin eater". Dust mites feed mainly on dead skin scales, of which each person secretes about one to two grams per day.
So far, 49 species of the Pyroglyphidae family have been found worldwide, 13 of which live in house dust, only six or seven more frequently. But there are other types of mites that can live in houses, especially in the tropics. The original habitat of house dust mites are bird nests, from there they have passed to human habitations and been taken away worldwide.
House dust mites are sexually separated, with the males being significantly smaller than the females. Females achieve a life weight of 5.8 micrograms, males only 3.5. After copulation, the females lay the eggs, but not as a clutch, but distributed individually over a long period. The lifespan of the females is highly dependent on temperature and humidity and also varies from species to species, ranging from about 30 to 100 days. During this time, they lay between 40 and 80 eggs, which develop over a larval stage and several nymphal stages to the sexually mature mites. The entire life span of the egg to the pubescent animal is very variable, it lasts under favorable conditions for about 30 to 50 days, but can extend at low temperatures up to 120 days.
Due to their microscopic size of just 0.1 millimeters, house-dust mites are barely visible to the naked eye. The mites themselves transmit no diseases and do not stand out negatively by sucking, biting or stinging.
Dust mites are found almost exclusively in human homes, but normally they can not survive outdoors. There are only a few exceptions, e.g. bird nests. Apartments are repopulated by mites carried away in clothing.
Their presence, however, is not a sign of lack of cleanliness - house-dust mites are among the natural roommates of the domestic environment of humans.
Most of the dust mites are in bed. There, the mattress and the rest of the upper bed are equally affected. Other localities are upholstered furniture, while in carpets usually only a few house dust mites are found. High densities can also occur in other substrates such as older books. The highest concentration can be found in mattresses and pillows, because there are plenty of skin flakes for food and plenty of moisture: A sleeping person excretes about 40 g of water per hour of sleep with the respiratory air and sweat.
On average, we share with over 3 million (!) dust mites our mattress and sheets!
Each individual mite produces about 20 droppings daily. In their approximately six-week life, the weight of mite feces adds up to 200 times the weight of the mite. Even in washed pillows there are still tens of thousands of mites. A pillow, from which only the cover is always cleaned, is loaded with up to half a million mites.
Every night, we whirl up the dried mite droppings. The finest particles are distributed then over the house-dust on the entire apartment. In only one gram of house dust are up to 15,000 mites. Dust mites are therefore the cause of the most common indoor allergen worldwide.
This is not a sign of lack of hygiene or cleanliness - but still a problem.