Dust mites are approximately 0.3 mm in length, too small to be seen with the naked eye. They are eight-legged and sightless, and live on skin scales and other debris. Mites excrete partially digested food and digestive enzymes as a fecal particle, which release allergens very rapidly. Most patients allergic to dust mites are actually allergic to the dust mite feces.

The mite fecal pellets are similar to pollen grains in three major ways:

• The fecal particles size
• The quantity of allergen carried
• The rate of proteins release

By being so similar to pollen grains, they are just the right size to cause allergies. Dust mites become a part of our environment and lifestyle because of their natural adaptations. Since they are entirely dependent on ambient humidity for hydration, and they are unable to search for environmental water supplies, they tend to live in places that "store" water. This may include carpets, sofas, mattresses and clothing. As humidity falls, mites withdraw from the surface and migrate to where there is more humidity; e.g., deeper in the mattress. Even in very dry conditions it may take months for mites to die and for their allergen levels to fall.

Avoiding contact with dust mites is the best way to protect against dust mite allergies.  This can include the use of dust mite covers on bedding, as well as HEPA or statically charged air filters (HEPA filters are typically more effective in combatting dust mites).  Immunotherapy, allergy shots and even over-the-counter antihistamines can help sufferers.