Dermatophagoides pteronyssinus and Dermatophagoides farinae,commonly known as house dust mites, are microscopic eight-legged creatures 0.3mm in length and invisible to the human eye. They are arachnids and relatives of spiders, not insects. Mites eat particles of skin and dander, so they thrive in places where there are people. A gram of house dust (approximately half of a teaspoon) contains as many as 1,000 dust mites. That same gram of dust can hold 250,000 of their fecal pellets. A dust mite will produce 20 fecal pellets per day, which is 200 times its own body weight in feces during its short lifetime. With millions of dust mites living in one bed, this means there are vast amounts of droppings there. These levels mean that virtually all dust mite-sensitive people will experience problems as a direct result of exposure to dust mites and their droppings in their mattress, pillows and duvet.
Dust mites are the largest offender in house dust worldwide and are the single, most important allergen associated with asthma. Thriving in humid, dark and warm environments, they prefer temperatures at or above 70 degrees Fahrenheit with a relative humidity of 75 to 80 percent. They will die if the humidity falls to below 50 percent and therefore are rarely found in dry environments. Dust mites make their homes primarily in pillows, mattresses, carpets and upholstered furniture, burrowing themselves deep into the fabric. Our homes are inundated with these microscopic, insect-like creatures and their debris, creating a hazardous environment for the allergy sufferer. It is virtually impossible to completely eliminate dust mites from your home, just as it is impossible to "cure" allergies.
As many as 10 percent of the general population and 90 percent of people with allergy-induced asthma are sensitive to dust mites. Recent studies in the United States suggest that at least 45 percent of young people with asthma are allergic to dust mites. Dust mites don't bite, cannot spread diseases and usually do not live on people. They are harmful only to people who become allergic to them. While usual household insecticides have no effect on dust mites, there are ways to reduce exposure to dust mites in the home.