There are several species of house dust mites, but the differences for practical purposes are not important. House dust mites are very, very tiny at about 1/64 inch long and off-white to cream in color. Despite being barely visible to the naked eye, their presence can impart significant and obvious health effects (allergies and asthma).

The developmental stages include the egg, 3 juvenile stages, and the adult. Development can be as quick as 22 days from egg to adult under warm conditions, and longer in cooler temperatures. House dust mites are extremely sensitive to low humidity and adapt to microclimates in places where humans spend time. They do not bite or feed on humans; their food source is sloughed skin cells, fungus and pollen, and occasional spilled food items. Sloughed skin particles are most concentrated around the mattress or other sleeping areas. Humans provide needed humidity.

House dust mites trigger allergies and are problematic for as many as 50 to 80 percent of asthmatic reactions. They may be responsible for allergies of more than 500 million people worldwide. Rates of asthma are rising, especially in children living in urban environments. Asthma can be deadly if not treated.