The house dust mite (sometimes abbreviated by allergists to HDM), is a cosmopolitan guest in human habitation. Dust mites feed on organic detritus such as flakes of shed human skin and flourish in the stable environment of dwellings. In nature they are killed by micro-predators and by exposure to direct sun rays. House dust mites are a common cause of asthma and allergic symptoms worldwide. The enzymes they produce can be smelled most strongly in full vacuum cleaner bags. The European house dust mite (Dermatophagoides pteronyssinus) and the American house dust mite (Dermatophagoides farinae) are two different species, but are not necessarily confined to Europe or North America.
A simple washing will remove most of the waste matter. Both being exposed to temperatures of over 60 degrees Celsius (140 degrees Fahrenheit) for a period of one hour, or freezing, will typically prove fatal to house dust mites; a relative humidity less than 50 may also be fatal. Ten minutes in a household clothes dryer at lethal temperatures has been shown to be sufficient to kill all the dust mites in bedding. House dust mites reproduce quickly enough that their effect on human health can be significant.
House dust mites consume minute particles of organic matter. House dust mites have a rudimentary alimentary system (no stomach) and require most digestion to occur outside their body. For this reason they secrete enzymes and deposit the fungus Aspergillus repens on dust particles, to enable the fungus to pre-digest the organic matter with its enzymes. House dust mites eat the same particle several times, only partially digesting it each time. Between feedings house dust mites leave particles to decompose further. Dust Mite fecal matter consists of these particles at the point where they are fully digested. A person sheds about 1.5 grams of skin cells and flakes every day (approximately 0.3-0.45 kg per year), which is enough to feed roughly a million house dust mites under ideal conditions.. House dust mites in bedding derive moisture from human breathing, perspiration, and saliva.
Some main signs of house dust mite allergies are itchiness, sneezing, inflamed/infected eczema, watering eyes, runny nose, (if asthma), lungs clogging up and hay fever.
It is commonly believed that the accumulated detritus from dust mites can add significantly to the weight of mattresses and pillows. While it is true that the fecal matter of dust mites will increase over time, there is no scientific evidence for these claims.
Allergy and asthma sufferers are also often advised to avoid feather pillows due to the presumed increased presence of the house dust mite allergen (Der p I). The reverse, however, is true. A 1996 study from the British Medical Journal has shown that polyester fibre pillows contained more than 8 times the total weight of Der p I and 3.57 times more micrograms of Der p I per gram of fine dust than feather pillows.