There is not a house without them!

The house dust mite (sometimes referred to by allergists as HDM)

Dust mites feed on organic detritus such as flakes of shed human skin and flourish in the stable environment of dwellings.

House dust mites are a common cause of asthma and allergic symptoms worldwide.

Some of the gut enzymes (notably proteases) produced by the house mite persist in their faecal matter, and can be strongly allergenic.

A mated female house dust mite can live for 70 days, laying 60 to 100 eggs in the last 5 weeks of her life.

In a 10 week life span, a house dust mite will produce approximately 2000 faecal particles and an even larger number of partially digested enzyme-covered dust particles.

Beds are a prime habitat (where 1/3 of life occurs). A typical used mattress may have anywhere from 100,000 to 10 million mites inside. (Ten percent of the weight of a two year old pillow can be composed of dead mites and their droppings.) Mites prefer warm, moist surroundings. A favorite food is both human and animal skin flakes. Humans shed about 1/5 ounce of dead skin (also known as dander) each week. About 80 percent of the material seen floating in a sunbeam is actually skin flakes. Also, bedroom carpeting and household upholstery support high mite populations.

The University of Manchester performed a 2005 medical study of pillows that found up to 16 species of fungi in a single pillow. They tested feather and synthetic pillows in a range of ages, finding thousands of spores of fungus per gram of pillow; more than is found on an average used toothbrush.

House dust mites reproduce quickly enough that their effect on human health can be significant.