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Medical Author:

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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Medical Editor:

William C. Shiel Jr., MD, FACP, FACR

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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In this Article

• Indoor allergens facts
• What are allergens?
• What actually is house dust?
• What are dust mites?
• What conditions are most favorable to dust mites?
• How do dust mites cause allergic symptoms?
• Can cockroaches cause allergic symptoms?
• What about allergies to molds?
• What about allergies to pets?
• What about allergies to indoor pollens and houseplants?
• Find a local Asthma & Allergy Specialist in your town
• Indoor Allergens Index

House dust is a mixture of diverse substances that can cause allergies. House dust is composed of a number of natural substances, including dried food particles, mold spores, pollen, fabric fibers, animal dander, and insect parts, especially those of dust mites and cockroaches. However, particles and debris from dust mites are the major source of allergens in dust. As is the case with other allergens, these particles contain proteins that are small enough to become airborne and inhaled.

Dust mites, which were discovered in 1964, are microscopic arachnids (resembling tiny spiders). They are about 1/3 mm in length and are not visible to the naked eye. They have eight legs, are blind, and naturally live indoors. Their presence does not indicate that the house is dirty. This is because usual cleaning procedures, such as vacuuming and dusting, do not eliminate them.

Dust mites have "sticky" pads at the ends of their legs that help them to firmly attach to fibers, which allow them to live deep within carpeting, upholstery, and mattresses. Most of the mites found in houses are from the Dermatophagoides family, with pteronyssinus and farinae being the most common species. (Dermatophagoides comes from Latin and means skin-eating. Pteronyssinus comes from Latin and means feather-loving. Farinae is Latin for flour.) Fortunately, dust mites do not bite, spread disease, or actually live on humans.

Dust mites thrive in warm, humid places. The ideal temperature for dust mites ranges from 65 to 80 degrees Fahrenheit, a common range for indoor room temperatures. Since dust mites have no means of drinking, they are totally dependent on the humidity surrounding them for water. They live best at a relative humidity above 55%. However, is is important to be aware that monitoring the humidity really isn't sufficient to control dust mites. As the humidity falls, dust mites will retreat from the surface. However, even in very dry conditions, it can take quite a few months to eliminate the dust-mite population.

Dust mites derive their food supply from human secretions and the skin cells we shed. (The average human sheds up to 1.5 grams of skin particles per day. A gram is about the weight of a paper clip.) The mites thrive in articles such as feather pillows, upholstered furniture, and stuffed animals that collect sloughed skin cells and secretions. The most favorable conditions for dust mite growth are found in the bedroom. Their favorite breeding grounds are mattresses, pillows, and box springs, as well as blankets, curtains, carpeting, and other fabric items in the room.

The perfect climatic conditions for dust mites occur in North America in the mid- and southern Atlantic coast, Gulf Coast, central Midwest, Pacific Northwest, and British Columbia. Dust mites are rarely found in dry climates where the elevation is over 5,000 feet above sea level.