A typical American two-year-old swallows roughly 80 milligrams of soil and household dust a day. A teenager or adult swallows about 30. Those are EPA’s own recommended planning figures, published in the 2017 update to its Exposure Factors Handbook.
The gap matters more than it looks, because the toddler doing the swallowing weighs maybe a fifth of what the adult weighs. Same house, same floor, same dust, roughly triple the intake into a body a fraction of the size.
That is the whole argument of this article in two numbers. House dust is not dirt that arrived from nowhere. It is a slow-accumulating sample of everything your household has carried in, worn out, sprayed, or let drift through a window, and the smallest person in the house gets the largest share of it.
The good news is that the two cheapest interventions are also the two best ones, and neither requires buying anything.
What house dust is
You have probably heard that house dust is mostly dead skin. It is a satisfying fact and it is not a safe thing to repeat, because the research that models dust formation does not describe it that way.
The most cited US model of how house dust forms, published in Environmental Science and Technology in 2009 by researchers at the University of Arizona, treats indoor dust as a mixture of three streams. The first is organic material generated inside, which includes shed skin cells and fibers from clothing and furnishings. The second is soil tracked in on footwear. The third is outdoor particulate matter that infiltrates with the air. Skin is on the list. It is one ingredient among several, not the headline.
A 2018 review of house dust and health added the rest of the inventory: plant material and pollen, microorganisms, insect debris, hair and fibers, plus particles and residues from combustion, furniture, interior finishes, electronics, cleaning products and personal care products.
The proportions shift from house to house, and no study has produced a universal recipe. What is consistent is that a meaningful fraction of indoor dust started outdoors. That fact is what makes the doormat and the shoe rack serious equipment rather than a housekeeping preference.
The best demonstration comes from the same 2009 paper. The authors reconstructed the sources of lead in house dust in Sacramento over several decades. In the early 1980s, airborne lead from leaded gasoline was dominant. As gasoline lead was phased out and airborne levels fell, the primary source of lead in house dust became resuspended soil and track-in from shoes. The lead did not disappear. It moved into the ground and came back in on the bottom of people’s feet.
The chemical inventory in an ordinary dust sample
Dust is a reservoir, and reservoirs collect what is around them. Researchers studying indoor exposure have learned to treat a single dust sample as a multi-contaminant archive.
A 2023 study by a Duke University team analyzed 124 house dust samples that had already been tested for flame retardants, phthalates, pesticides and per- and polyfluoroalkyl substances. The team then went looking for azobenzene disperse dyes, which shed from clothing and upholstery, and found twelve target dyes in between 11 and 89 percent of the samples. The point is that one scoop of floor dust supported five separate contaminant investigations.
A few of the families are worth naming specifically:
Lead. EPA says the most common source of lead exposure in the United States is lead-based paint dust in older homes. Paint in good condition is not the problem. Paint that is chalking, rubbing at a friction point, or being disturbed is.
Pesticides. EPA’s indoor air guidance cites a survey finding that 75 percent of US households had used at least one pesticide product indoors in the previous year, and notes that the quantity of pesticide found in homes “appears to be greater than can be explained by recent pesticide use in those households.” EPA lists contaminated soil and dust brought in from outside as one explanation, along with surfaces that absorb a product and release it slowly afterward. Lawn and garden products get tracked in on shoes and paws.
PFAS. A 2016 study measured 20 of these compounds in dust from 41 homes in Canada, the Czech Republic and the United States, with the North American homes generally higher than the Czech ones. Median concentrations of the two most familiar compounds ran in single-digit to low-teens nanograms per gram of dust. PFAS in drinking water is a separate and much larger regulatory story, and article 699 covers it.
Flame retardants, plasticizers and textile chemicals. These come off the objects in the room. Foam cushions, electronics casings, vinyl, carpet backing and clothing all shed.
Two quick boundaries. Dust mites are alive, they are an allergen rather than a contaminant, and article 690 handles them. Mold is a water problem wearing a dust costume, and article 691 owns it.
Why small children get the highest dose
The usual explanation is that children are more fragile. That is partly true, and the CDC does note that growing bodies absorb more lead than adult bodies do. But fragility is the smaller half of the story. The larger half is dose, and the dose is a product of where children put their hands and how close their faces are to the floor.
Hand to mouth
Infants and toddlers mouth their hands, their toys and whatever else is within reach, and they do it constantly. That behavior converts settled dust into swallowed dust. EPA’s Exposure Factors Handbook puts the central estimate for children aged one to under six at about 80 milligrams of soil and dust a day, with an upper-percentile figure of 200. For people twelve and older the central figure drops to about 30 milligrams.
EPA is candid that these are rough. The handbook rounds its values to one significant figure and rates its own confidence in them as low, because measuring how much dirt a toddler eats is hard. The direction of the difference is not in doubt. The precision is.
Floor-level breathing
The second route is less obvious and better measured than most people would guess. A chamber study published in 2018 used a mechanical crawling infant robot on carpet and sampled the air at the robot’s breathing height. During crawling, bacterial and fungal levels in the infant breathing zone ran on average 8 to 21 times higher than in an adult’s breathing zone in the same room.
A related 2017 study from the same research group quantified what that means for dose. Per kilogram of body mass, an infant crawling on carpet received nearly four times the respiratory tract deposited dose of resuspended biological particles that a walking adult did. A follow-up in 2021 documented a pronounced vertical difference in particle concentration between the near-floor zone and the bulk air of the room.
Put the two routes together and the picture is clear. A crawling child lives inside a localized cloud of whatever is in the carpet, breathes it in at a higher rate per unit of body weight, and then eats a portion of it off their hands. Nothing about this requires the child to be unusually vulnerable. It is geometry and behavior.
Intervention one: shoes come off at the door
This is the highest-return change available to a household, and it is free.
EPA’s own guidance for reducing lead exposure at home says to place doormats at entryways, remove shoes before entering, and leave shoes outside if they may be carrying lead dust. The 2009 Sacramento lead reconstruction is the evidence behind why that works: once airborne sources decline, track-in becomes the dominant route by which outdoor contamination reaches indoor dust.
Shoes also carry whatever is on the ground where you walk, which includes lawn and garden pesticide residue, road grit, and soil that may carry lead from decades of paint weathering off nearby buildings.
Make it easy rather than virtuous. A shoe rack by the door, a bench to sit on, and a pair of indoor shoes for anyone who dislikes stocking feet will do more than a sign asking guests to comply. If you have a crawling baby, enforce the rule with visitors too, politely and without a speech.
Intervention two: damp methods beat dry ones
Dry dusting and sweeping do not remove dust. They relocate it, and a good portion of what they relocate goes into the air you are standing in.
The clearest measurement of this comes from a 2002 study of post-abatement cleaning in a test chamber, funded in part by HUD. When researchers dry swept after disturbing lead paint, airborne lead mass rose by somewhere between 65 and 220 percent. When they wet swept the same debris, the increase stayed at or below 22 percent.
The same study found something else worth knowing. HEPA vacuuming cut airborne lead by a factor of 15 to 20, which is a large effect, but it was not by itself enough to bring floor lead loading below the clearance level that applied at the time. Wet mopping after the vacuuming was what got the floors there.
That is the sentence to remember: you cannot vacuum your way out of a lead problem. A vacuum is a useful part of a sequence that ends with something wet.
EPA’s household advice follows the same logic. Wipe hard surfaces with a damp cloth. Wet mop floors. Use a vacuum without beater bars. If there is visible paint debris, do not dry sweep at all. Which machine and which filter to buy is article 686’s subject, and the honest summary is that technique matters more than the model.
What this changes about your routine
- Swap the feather duster and the dry static cloth for a damp microfiber cloth you rinse out.
- Sweep only after misting, or skip the broom and go straight to a damp mop.
- Pay attention to window sills and the troughs below them. They collect outdoor particles and, in older houses, paint debris from the single most abraded surface in the building.
- Give the floor near doors more attention than the middle of the room. That is where track-in lands.
- Treat textiles as storage. Rugs, upholstery, curtains and soft toys hold more dust per square foot than hard surfaces because they have vastly more surface area and more places for particles to lodge. Washing them is a dust intervention, not just a laundry task.
- Reduce the number of horizontal surfaces holding objects. Clutter is not a moral failing, but every item is a shelf for dust and an obstacle to wiping.
Renovation and sanding: the biggest short-term dust hazard there is
Everything above is about a slow accumulation. Renovation is different in kind. A weekend of sanding old paint can put more lead into a home’s dust than years of ordinary living, and the people most likely to do it without protection are homeowners working on their own houses.
Here is the regulatory shape of the problem. EPA’s Renovation, Repair and Painting rule covers housing and child-occupied facilities built before 1978. Anyone paid to disturb painted surfaces in those buildings must work for a certified firm with trained workers using lead-safe work practices, and EPA states that this includes sole proprietors. The rule generally does not apply to homeowners doing the work in their own pre-1978 home.
Read that last sentence again, because it is the gap. The federal government requires a trained, certified crew to open up your neighbor’s pre-1978 wall, and requires nothing of you when you open up your own. The rule exists because the hazard is real, not because contractors are uniquely careless.
What lead-safe work looks like
EPA publishes guidance for do-it-yourselfers, and the practices are more specific than most people expect. The core of it:
Before. Clear the room of furniture, rugs, curtains, food and clothing, and cover what cannot be moved. Put plastic sheeting on the floor. Close and seal doors into the work area. Turn off forced-air heating and cooling, close windows and cover vents with plastic so the system does not distribute dust through the house.
During. Mist surfaces before sanding, scraping, drilling or cutting, which is the single most effective dust control available. Use wet-dry sandpaper or a sanding sponge rather than dry methods. If you use a heat gun, EPA specifies a low-temperature one, under 1,100 degrees Fahrenheit. Fit power tools with HEPA vacuum attachments. Wear a disposable N-100 respirator, coveralls, shoe covers, gloves and eye protection. Do not eat, drink or smoke in the work area, and wash hands and face every time you stop.
After. Clean at the end of every working day rather than at the end of the project. Seal waste in heavy plastic and tape it shut. HEPA vacuum everything, including furniture and fixtures, then wipe every surface with wet disposable cloths until the cloths come up clean. Wash your work clothes separately from the family’s laundry. If you want confirmation rather than hope, you can hire a certified technician to do post-renovation dust-lead testing.
The numbers behind the clearance test
EPA tightened these standards in October 2024. The agency now treats any reportable level of lead in dust, as measured by a laboratory recognized under its National Lead Laboratory Accreditation Program, as a dust-lead hazard. For post-abatement clearance it lowered the action levels from 10 to 5 micrograms per square foot on floors, from 100 to 40 on window sills, and from 400 to 100 in window troughs.
Those are regulatory numbers, which is a different bucket from advice. They apply to formal abatement work and to the laboratories that measure it, not to your Saturday. But they tell you something useful about scale: the amount of lead dust that counts as a problem on a floor is five micrograms spread over a square foot, which is far less than you could see.
The CDC’s position on the health side is just as direct. There is no known safe blood lead level in children. CDC uses a blood lead reference value of 3.5 micrograms per deciliter to identify children with higher levels than most, and estimates that roughly 500,000 US children are at or above it.
Lead in drinking water travels an entirely different route, through service lines and plumbing rather than paint, and article 698 covers it.
When to stop cleaning and call someone
Cleaning is the right response to ordinary dust. These situations are not ordinary dust, and they call for a professional rather than a better mop.
- Peeling, chipping, chalking or cracking paint in a home built before 1978. Hire a certified lead-based paint inspector or risk assessor. Scraping it yourself to tidy it up is the exact action that creates the hazard.
- Any planned work that will disturb painted surfaces in a pre-1978 home. Use an EPA lead-safe certified firm. EPA maintains an online search for certified firms and for training providers.
- A child under six living in older housing, especially if there has been recent renovation or there is damaged paint. Ask the pediatrician about a blood lead test and say why you are asking. A blood test is the only way to know, and it is a routine draw.
- Pregnancy in a house being renovated. Stay out of the work area entirely and talk to your clinician about exposure.
- Friction surfaces in an old house. Windows that are painted and still get opened, and doors that rub, grind paint into dust every time they are used. That is why window sills and troughs show up in every lead standard.
Two habits that beat the equipment
Change two habits and leave the rest alone.
Take shoes off at the door, because a large share of what ends up in your dust came in on the bottom of somebody’s feet. And when you clean, make the last step a wet one, because dry methods move dust into the air and a damp cloth takes it out of the house.
Everything else, the air cleaners and the vacuums and the fifteen-product cleaning routines, sits downstream of those two. A household that gets them right and buys nothing is in better shape than one that buys equipment and keeps walking across the living room in street shoes.
Sources
- U.S. Environmental Protection Agency. “Exposure Factors Handbook, Chapter 5: Soil and Dust Ingestion (2017 update, EPA/600/R-17/384F).” epa.gov
- U.S. Environmental Protection Agency. “Learn about Lead.” epa.gov
- U.S. Environmental Protection Agency. “Reduce the Risk of Lead Exposure at Home.” epa.gov
- U.S. Environmental Protection Agency. “Lead Renovation, Repair and Painting Program.” epa.gov
- U.S. Environmental Protection Agency. “Lead-Safe Renovations for Do-It-Yourselfers.” epa.gov
- U.S. Environmental Protection Agency. “Hazard Standards and Clearance Levels for Lead in Paint, Dust and Soil (TSCA Sections 402 and 403).” epa.gov
- Centers for Disease Control and Prevention. “Childhood Lead Poisoning Prevention.” cdc.gov
- U.S. Environmental Protection Agency. “Pesticides' Impact on Indoor Air Quality.” epa.gov
- Environmental Science & Technology, 2009 (PubMed). “Layton DW, Beamer PI. "Migration of contaminated soil and airborne particulates to indoor dust." DOI: 10.1021/es9003735.” doi.org
- Environmental Pollution, 2023 (PubMed). “Overdahl KE, et al. "Characterizing azobenzene disperse dyes and related compounds in house dust and their correlations with other organic contaminant classes." DOI: 10.1016/j.envpol.2023.122491.” doi.org
- Environment International, 2016 (PubMed). “Karaskova P, et al. "Perfluorinated alkyl substances (PFASs) in household dust in Central Europe and North America." DOI: 10.1016/j.envint.2016.05.031.” doi.org
- Applied Occupational and Environmental Hygiene, 2002 (PubMed). “Grinshpun SA, et al. "Efficiency of final cleaning for lead-based paint abatement in indoor environments." DOI: 10.1080/104732202753438306.” doi.org
- Microbiome, 2018 (PubMed). “Hyytiainen HK, et al. "Crawling-induced floor dust resuspension affects the microbiota of the infant breathing zone." DOI: 10.1186/s40168-018-0405-8.” doi.org
- Environmental Science & Technology, 2017 (PubMed). “Wu T, et al. "Infant and Adult Inhalation Exposure to Resuspended Biological Particulate Matter." DOI: 10.1021/acs.est.7b04183.” doi.org
- Environmental Science & Technology, 2021 (PubMed). “Wu T, et al. "Particle Resuspension Dynamics in the Infant Near-Floor Microenvironment." DOI: 10.1021/acs.est.0c06157.” doi.org
- Nihon Eiseigaku Zasshi (Japanese Journal of Hygiene), 2018 (PubMed). “Araki A, et al. "House Dust and Its Adverse Health Effects." DOI: 10.1265/jjh.73.130.” doi.org