House Dust Mite
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. Dust mites are considered to be the most common cause of asthma and allergic symptoms worldwide. The enzymes they produce can be smelled most strongly in full vacuum cleaner bags.
The house dust mite's partially digested food, and fecal matter, is one of the most significant sources of allergens, implicated in allergic asthma, rhinitis, conjunctivitis and dermatitis. One of the more important proteins responsible for the allergic reaction is DerP1, a protease digestive enzyme found in mite feces. Dust mites bodies, made of chitin, are also allergens. Immunotherapy or "allergy shots" have been helpful for sufferers of hay fever and asthma. Steam cleaners may be effective at reducing enzyme allergens since the heat of the steam breaks down (decomposes) the compound. Prolonged exposure of skin to the proteins in dust mite fecal matter reduces its barrier function; this weakness can create a point of entry for allergens and irritants, leading to inflammation and itchiness or pruritis.