Dust mites (primarily Dermatophagoides pteronyssinus and Dermatophagoides farinae) are microscopic arachnids, barely visible to the naked eye (about 0.

3 mm in length), that feed on shed human and pet skin scales and dander.

Dust mites themselves do not bite, suck blood, or transmit infectious diseases — the primary harm to humans comes from their fecal pellets.

Each dust mite produces about 2,000 fecal pellets (each about 20 microns in size) during its approximately 2–3 month lifespan — these fecal pellets contain potent allergenic proteins (Der p 1 and Der f 1).

When the fecal pellets dry out and become airborne dust, they can trigger allergic asthma and rhinitis when inhaled by sensitized individuals.

Dust mites are one of the most important triggers of indoor allergies and asthma — in temperate, humid regions, approximately 50–80% of asthma patients are allergic to dust mites.

The preferred living conditions for dust mites are: temperatures of 20–25 °C and relative humidity of 70–80% (they absorb water from the air through their body surface; humidity below 50% causes dehydration and death).

Dust mites are concentrated in: mattresses, pillows, comforters, carpets, upholstered sofas, and plush toys — these are places where skin scales accumulate and remain warm and moist.

A two-year-old mattress can contain hundreds of thousands to millions of dust mites.