What Are Dust Mites?


American College of Allergy, Asthma, and Immunology

Tiny microscopic creatures called dust mites are an important cause of allergic reactions to house dust. They belong to the family of eight-legged creatures called arachnids. This family also includes spiders, chiggers and ticks. Dust mites are hardy creatures that live well and multiply easily in warm, humid places. They prefer temperatures at or above 60°F with a relative humidity of 50-60 percent or more and die when the humidity falls below 25-30 percent.

As many as 10 percent of the general population and 90 percent of people with allergic 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.

People who are allergic to dust mites react to proteins in the bodies and feces of the mites. These fecal particles are found in the highest concentrations in pillows, mattresses, carpeting, and upholstered furniture. They float into the air when anyone vacuums, walks on a carpet or disturbs bedding, but settle out of the air once the disturbance is over. Dust mite-allergic people who inhale these particles frequently experience allergy symptoms. In fact, a dust mite allergic patient who sleeps for 8 hours every night spends one third of his life with his nose in direct contact with a pillow loaded with dust mite particles!

There may be many as 19,000 dust mites in one gram of dust, but usually between 100 to 500 mites live in each gram. (A gram is about the weight of a paper clip.) Each mite produces about 10-20 waste particles per day and lives for 30 days. Egg-laying females can add 250-300 new mites to the population during their lifetime. 50% of the eggs the female lays are of the female gender and consequently each of these dust mites lays 250-300 new eggs and the cycle continues creating a population of millions of dust mites in a very short period of time, generally 6-8 months depending upon environmental factors.

Mites eat particles of skin and dander, so they thrive in places where there are people and household pets. Dust mites don’t bite, cannot spread diseases and usually do not live on people. They are harmful to people who become allergic to them as well as to people who suffer from allergies, asthma, upper respiratory illnesses, skin diseases and other related problems. In sufficient quantities– which develop after a short period of time (a typical, untreated bed can contain millions of dust mites)– dust mites may cause problems ranging from headaches, to itchy red eyes, to rough or irritated throats, and in some cases morning depression or fatigue– for even the healthiest of people. While usual household insecticides have no effect on dust mites, there are ways to reduce exposure to dust mites in the home.

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