House dust is a surprisingly complex mixture of organic matter, synthetic chemicals, living organisms, and particles tracked in from outdoors. Roughly 69% of it is organic material, including skin fragments, bacteria, fungi, and fibers from clothing and furniture. The rest is mineral content like silica and calcium carbonate, along with metals such as aluminum and zinc. What makes dust genuinely interesting, and occasionally concerning, is the sheer variety of substances packed into those gray clumps under your couch.
Skin, Fibers, and the Organic Bulk
The single largest category of house dust is organic matter. Shed skin cells are a well-known contributor, but they share space with hair, food crumbs, insect fragments, plant material, and an enormous quantity of textile fibers. Every time you walk across carpet, sit on upholstered furniture, or fold laundry, tiny fibers break free and settle into your dust. Studies of settled house dust in residential buildings found that fibrous particles account for over 90% of what’s visible under a microscope, with small fragments making up roughly 7%.
The inorganic portion is mostly mineral particles, dominated by silica (silicon dioxide) and calcium carbonate, both common components of soil and rock. These get carried indoors on shoes, through open windows, or on air currents. On days with minimal indoor activity, outdoor sources can account for 40 to 60% of the larger particles settling in your home. On high-activity days with cooking, cleaning, and people moving around, indoor sources dominate, generating over 90% of the larger particles.
Microplastics in Every Room
One of the more recent discoveries about house dust is how thoroughly it’s laced with microplastics. These are tiny synthetic polymer fragments shed from everyday household items, especially textiles. Research on settled indoor dust found that polyester (PET) was the most frequently detected polymer, making up about 64% of synthetic fibers in dust samples. Polyacrylonitrile, used in acrylic fabrics, accounted for another 9%. Nylon, polypropylene, and polyethylene also showed up regularly.
Synthetic polymers were detected in 4 to 52% of house dust samples by weight, depending on the home. Cellulose fibers, from cotton clothing, paper products, and cardboard, were even more prevalent, appearing in 26 to 76% of samples. Less common but still present were alkyd resin (from paints), polyurethane (from foam cushions), and polystyrene. You’re essentially breathing in a low-level inventory of every synthetic material in your home.
Bacteria and Fungi From Your Own Body
House dust carries a distinct microbial signature that’s very different from outdoor air. Indoor dust is dominated by bacteria associated with human skin and the respiratory tract. The five most abundant bacterial groups found in residential dust are Streptococcus, Staphylococcus, Corynebacterium, Lactobacillus, and Massilia. The first four are all gram-positive bacteria commonly found on human skin, in saliva, and in the gut. You are, in a very real sense, the primary source of bacteria in your own dust.
The fungal community tells a slightly different story. Indoor dust tends to be dominated by molds like Aureobasidium and Leptosphaerulina, along with Aspergillus, Epicoccum, and Cryptococcus. One fungus worth noting is Malassezia, a yeast that naturally lives on human skin and contributes to dandruff. It shows up regularly in dust samples, another sign that your body seeds the environment around you. These fungi typically arrive from a mix of indoor and outdoor sources: some drift in through windows, while others grow in damp spots or shed from your own skin.
Dust Mites and Pet Allergens
Dust mites are microscopic arachnids that feed on shed skin cells and thrive in warm, humid environments like mattresses, pillows, and upholstered furniture. Their fecal pellets and body fragments are potent allergens. Researchers use concentration thresholds to gauge risk: above 2 micrograms of mite allergen per gram of dust, people can become sensitized over time. Above 10 micrograms per gram, active allergy symptoms are likely in susceptible individuals.
Pet allergens are remarkably persistent and mobile. A national survey of U.S. homes found dog allergen in 100% of homes tested and cat allergen in 99.9%, regardless of whether a pet actually lived there. Even in homes without any indoor dog, measurable dog allergen appeared on beds, floors, and sofas. For cat allergen, 55.7% of homes without a cat still had concentrations above the sensitization threshold. These proteins travel on clothing, are carried in on visitors, and persist in dust for months. If you’re allergic to cats or dogs, simply avoiding pet ownership doesn’t eliminate exposure.
Chemical Pollutants From Consumer Products
Dust acts as a reservoir for chemicals that slowly off-gas or flake off from furniture, flooring, electronics, and personal care products. A large meta-analysis of U.S. studies found that phthalates, used as plasticizers in vinyl flooring, food packaging, and fragranced products, occur in house dust at concentrations several orders of magnitude higher than any other chemical class. They are by far the dominant synthetic chemical in residential dust.
After phthalates, the next most concentrated chemicals are phenols (found in disinfectants and plastics), flame retardants (added to furniture foam, electronics, and children’s products), and synthetic fragrances from cleaning supplies, air fresheners, and personal care items. PFAS, the “forever chemicals” used in nonstick coatings and water-resistant fabrics, were detected in the lowest concentrations of the chemical classes studied, but they were still present in most homes. Researchers have cataloged at least 45 individual consumer product chemicals with measurable concentrations in typical house dust.
Lead and Heavy Metals
In older homes, lead is one of the most consequential things in dust. Deteriorating lead-based paint, which was common in homes built before 1978, sheds tiny particles that accumulate in floor dust and on window sills. Young children are especially vulnerable because they spend time on floors and put their hands in their mouths frequently.
The EPA updated its dust-lead standards in a final rule effective January 2025. Under the new framework, any reportable level of lead detected in floor dust from a residential home or child-occupied facility now qualifies as a dust-lead hazard. For post-abatement clearance (after lead paint removal), floors must test below 5 micrograms per square foot, interior window sills below 40 micrograms per square foot, and window troughs below 100 micrograms per square foot. These thresholds are substantially stricter than earlier standards, reflecting growing evidence that no level of lead exposure is safe for children.
Reducing What Builds Up
You can’t eliminate dust entirely, but you can reduce the concentration of its more harmful components. HEPA-filtered vacuums capture particles as small as 0.3 microns with 99.97% efficiency, which makes them effective at removing allergens, lead particles, and fine microplastic fibers that standard vacuums would blow back into the air. Damp mopping hard floors picks up what vacuuming misses, since dry sweeping tends to redistribute fine particles rather than remove them.
Ventilation matters too. Opening windows increases the contribution of outdoor particles like pollen and soil, but it also dilutes indoor-generated pollutants like phthalates and flame retardants that build up in sealed, climate-controlled homes. Washing bedding in hot water weekly reduces dust mite populations significantly, since mites concentrate where moisture and skin cells are most abundant. Keeping indoor humidity below 50% makes your home less hospitable to both dust mites and mold growth. Removing shoes at the door cuts down on tracked-in soil, pesticides, and lead particles from older outdoor paint.