Sources of House Dust Mites
House dust mites thrive primarily in bedding, upholstered furniture, carpeting, and soft toys—anywhere humans shed skin cells—and their proliferation is driven by humidity levels above 50% and modern energy-efficient home construction. 1
Primary Food Source and Habitat
The principal food source of house dust mites (predominantly Dermatophagoides pteronyssinus and D. farinae) consists of exfoliated human skin cells. 1 Consequently, mites are most abundant in locations where skin cells are shed, including:
- Bedding (mattresses, pillows, sheets) 1
- Fabric-covered furniture 1
- Carpeting (especially wall-to-wall carpeting) 1
- Soft toys and stuffed animals 1
Research confirms that the most heavily used fabric-upholstered furniture and carpeted floor areas in living rooms, family rooms, and bedrooms harbor significantly higher mite levels. 2 Interestingly, mattresses were not found to be the major foci for mites in one longitudinal study, with upholstered furniture and carpets showing higher densities. 2
Environmental Factors Promoting Mite Growth
Humidity Requirements
To reproduce, dust mites generally require a relative humidity of 50% or greater. 1 The geographic and seasonal distributions of dust mites are determined by their need for adequate humidity. 3 Mites are present in homes in humid geographical areas and are rare or absent in drier climates unless humidity is artificially raised. 4
Mite density exhibits seasonal fluctuation, with highest density occurring in humid summer months and lowest density during the drier, late heating season. 2
Modern Construction Practices
Recent changes in home construction and housecleaning methods have created environments conducive to dust mite proliferation, including: 1
- Enhanced energy efficiency in buildings leading to reduced ventilation and increased humidity 1
- Wall-to-wall carpeting 1
- Furnished basements 1
- Use of water for laundry that is not hot enough to kill mites (below 130°F) 1
Geographic Distribution
The most prevalent house dust mites, D. pteronyssinus and D. farinae, are ubiquitous except in arid or semiarid climates and regions of higher altitudes. 1 Most homes contain multiple species, and the most prevalent mite species and allergen in homes differ geographically, between homes within a geographical region, and among areas within a home. 4
Critical Pitfall: Carpeting Over Concrete
Carpeting installed over a concrete slab will inevitably become contaminated with both mites and fungi because of condensation and is best avoided if possible. 1 This represents a particularly problematic source due to moisture accumulation.
Distribution Within Substrates
Significantly higher mite levels occur on carpeted floors than on noncarpeted floors. 2 Their distribution within substrates is further determined by their avoidance of light. 3 Dust mite fecal pellets easily become airborne when their reservoir is disturbed, although they rapidly settle once the disturbance stops. 1
Institutional Settings
Generally speaking, dust mite allergen levels are low in public buildings and transportation compared to levels in homes. 4 Hospital environments can maintain very low mite density through maintenance of low relative humidity, use of low-pile carpets, and good housekeeping and laundering practices. 5