What Are House Dust Mites?
House dust mites are microscopic eight-legged arachnids (approximately 0.25–0.33 mm in size, barely visible to the naked eye) that live in indoor environments and feed primarily on human skin cells, making them ubiquitous inhabitants of homes worldwide and the most common cause of indoor allergic disease. 1, 2
Biological Classification and Species
- House dust mites belong to the Arachnid class and are related to spiders and ticks, not insects. 2
- The major allergenic species include Dermatophagoides pteronyssinus (the European house dust mite), Dermatophagoides farinae, Euroglyphus maynei, and Blomia tropicalis. 2, 3, 4
- These two Dermatophagoides species are immunologically cross-reactive, meaning they share similar allergen proteins. 5
- Their life cycle spans approximately 3 months, progressing through egg, larval, protonymph, tritonymph, and adult stages. 2
Where They Live in Your Home
House dust mites concentrate in specific locations where their food source accumulates:
- Bedding (mattresses and pillows, especially the upper sectors closest to sleeping occupants) is the primary habitat. 1
- Upholstered furniture serves as a major reservoir for mite populations. 1
- Wall-to-wall carpeting provides extensive colonization habitat throughout homes. 1
- Soft toys and stuffed animals support significant mite populations. 1
- Textile articles affected by mold provide additional nutritional substrate. 3
What They Eat and Why They're Everywhere
- Human skin cells (dander) serve as the principal food source for house dust mites. 1, 6
- Humans continuously shed dead skin, creating a perpetual food supply wherever people spend time. 6
- This feeding relationship means dust mites and humans will continue to co-exist indefinitely as part of our indoor environment. 6
Environmental Conditions They Need to Survive
Humidity is the critical limiting factor:
- Mites require relative humidity ≥ 50% to reproduce, with optimal reproduction occurring at approximately 85% RH. 1
- Geographic distribution is determined by humidity needs—mites are absent or rare in arid, semi-arid climates and high altitudes where low ambient humidity prevents their survival. 1
- Mites avoid light and concentrate in dark, humid microhabitats within homes. 2
Why Modern Homes Have More Mites
Recent construction trends have inadvertently created ideal mite habitats:
- Enhanced energy-efficiency measures reduce ventilation and raise indoor humidity, facilitating mite survival. 1
- Widespread use of wall-to-wall carpeting increases available habitat. 1
- Furnished basements in humid regions provide optimal conditions. 1
- Installing carpet over concrete slabs leads to condensation-driven moisture accumulation, inevitably contaminating the carpet with both mites and fungi—this practice should be avoided. 1
Health Impact: Why Mites Matter Medically
House dust mites are the most common and potent allergen source in indoor environments:
- Allergens are contained primarily in mite fecal pellets, but also in shed exoskeletons and decaying body fragments. 2
- These allergen-containing particles contact the epithelium of eyes, nose, lower airways, skin, and gut, inducing sensitization and symptoms. 2
- Clinical conditions resulting from mite exposure include asthma, rhinitis, sinusitis, conjunctivitis, tracheitis, bronchitis, and atopic dermatitis. 2, 3
- Mite allergen levels above 2 μg/g settled dust are considered a risk factor for sensitization. 5
- Children under 10 years of age are particularly affected by these allergies. 3
- Allergies peak in midsummer and early autumn when mite populations are highest. 3
How Allergens Become Airborne
- When mite reservoirs are disturbed (vacuuming, foot traffic, bed making), fecal pellets become airborne but settle quickly once disturbance stops. 1
- Ordinary vacuuming has minimal impact on allergen concentrations because pellets readily pass through low-efficiency vacuum bags and become widely dispersed. 1
- This explains why symptoms often worsen during cleaning activities. 5
Important Biological Properties
Mite allergens have unique properties that enhance their allergenic potential:
- Proteolytic (protein-cleaving) activity that breaches epithelial tight junctions and stimulates protease-activated receptors. 2
- These proteases induce pruritus, epithelial dysfunction, and cytokine release. 2
- Components including chitin, unmethylated DNA, and endotoxin activate innate immune pattern recognition receptors and act as adjuvants promoting sensitization. 2
- Homology with invertebrate tropomyosins can cause cross-reactivity with shrimp, snails, and other invertebrates. 2