House Dust Mite

Dermatophagoides pteronyssinus — the European house dust mite — and her sister species D. farinae (the American house dust mite) are microscopic arachnids (~0.3 mm) that inhabit human dwellings worldwide. The species feed on the approximately 1.5 grams of dead skin cells that the average human sheds every day, with secondary feeding on fungi, yeasts, and bacteria. Population densities can be enormous: a typical bed mattress contains 1-10 million dust mites, with peak abundance in pillows, mattresses, carpets, upholstered furniture, and curtains. The species cannot drink — she absorbs water vapor directly from atmospheric humidity through specialized cuticular structures, which is why dust mite populations crash in arid climates and surge in humid climates. Mite fecal pellets and shed exoskeletons (allergens Der p 1, Der p 2, Der f 1, Der f 2) are the dominant indoor allergen worldwide, triggering allergic rhinitis, atopic dermatitis (eczema), and allergic asthma in an estimated 100-150 million people globally. The species is harmless in any direct sense — no bite, no venom, no disease transmission — but the immune-system response to mite particulate is one of the most consequential public-health issues in indoor environmental health.