Dust mites are microscopic creatures that belong to the same class (Arachnida) as spiders and ticks (they have eight legs, not six like insects). They feed primarily on dead skin cells regularly shed by humans and animals. Dust mites thrive in places where their primary food source is most likely to be found: on mattresses, pillows, bedcovers, carpets, upholstered furniture, stuffed toys, clothes, or other fabric items in the home.Unlike insects such as cockroaches, mites are not capable of ingesting water; in order to obtain water, they must absorb it from the air. For this reason, they thrive in humid environments, ranging from 55% to 75% relative humidity. Ideal temperatures for dust mites are between 68º and 77º F. The growth of dust mites can vary on a seasonal basis, or from room to room within a house, depending largely on variations in relative humidity, availability of food sources, and temperature. Mites take about one month to develop from an egg into an adult and have an adult life span of about two to four months. A single adult female may lay up to 100 eggs.
Mite waste products contain an allergen (a substance that causes an allergic immune reaction) that, according to the Asthma and Allergy Foundation of America, adversely affects about 20 million Americans. Sensitive individuals become exposed to this allergen when they inhale household dust, which contains dust mites and their waste products. Exposure to dust mites can trigger an attack in an asthmatic who is sensitive to the dust mite allergen. (Other asthmatics may not be affected by dust mites.) For persons allergic to dust mite allergen, exposure can cause allergic rhinitis (hay fever), which is characterized by nasal congestion, itching, and sneezing. In addition, exposure to dust mites may cause children who are predisposed to develop asthma to do so. (This predisposition is not fully understood, but appears to depend upon a combination of hereditary and environmental factors.) For more information on asthma and allergies, see Asthma, Allergies, and Respiratory Illnesses.