Indoor Air Quality: The Invisible Health Factor

The Air Inside Your Walls

Here’s a number that stops people cold: according to the EPA, indoor air is typically 2 to 5 times more polluted than outdoor air. In some cases, 100 times worse. You spend roughly 90% of your life indoors. That means the air inside your home, office, and car is — by volume of exposure — the most significant air you breathe.

Yet almost nobody tests it. We test our water, monitor our food, track our steps. The air we pull into our lungs 20,000 times a day? We assume it’s fine because we can’t see it.

Functional medicine treats air quality as a foundational exposure. Chronic respiratory inflammation, unexplained fatigue, brain fog, recurrent sinus infections, skin conditions, and even cardiovascular disease can have their roots in what’s floating invisibly through your living space.

The Major Indoor Pollutants

Volatile Organic Compounds (VOCs)

VOCs are carbon-containing chemicals that evaporate at room temperature. They are everywhere indoors:

• Formaldehyde: off-gasses from pressed wood products (plywood, MDF, particle board), laminate flooring, permanent-press fabrics, and some insulation. Classified as a Group 1 carcinogen by IARC. That “new house smell” or “new furniture smell” is largely formaldehyde and other aldehydes — and it’s not a sign of freshness, it’s a sign of chemical exposure.
• Benzene: found in paints, lacquers, adhesives, detergents, tobacco smoke, and attached garages (gasoline fumes). A known human carcinogen causing leukemia.
• Toluene and xylene: from paints, thinners, adhesives, nail polish, and some cleaning products. Neurotoxic at chronic low doses.
• Fragrance compounds: air fresheners, scented candles, plug-ins, laundry products. Steinemann’s 2016 study in Air Quality, Atmosphere & Health found that the top-selling fragranced consumer products emitted an average of 17 VOCs per product, including carcinogens and endocrine disruptors — none required to be listed on the label because “fragrance” is considered a trade secret.

Key insight: VOC levels in a new home can be 10-100x higher than in an older home. A new building or major renovation requires aggressive ventilation for weeks to months.

Particulate Matter (PM2.5 and PM10)

Particles smaller than 2.5 microns (PM2.5) penetrate deep into the alveoli of your lungs and cross into the bloodstream. Sources include cooking (especially frying and high-heat methods), candles, incense, fireplaces, tobacco smoke, and outdoor air infiltrating the building. Long-term PM2.5 exposure is associated with cardiovascular disease, stroke, lung cancer, and cognitive decline. A 2020 study in Science Advances (Braithwaite et al.) linked PM2.5 exposure to increased dementia risk.

Carbon Monoxide (CO)

The silent killer. Produced by gas stoves, furnaces, water heaters, fireplaces, and attached garages with running vehicles. At low chronic levels that don’t trigger acute poisoning, CO still binds to hemoglobin and reduces oxygen delivery. Symptoms mimic many functional medicine complaints: headache, fatigue, dizziness, brain fog.

Radon

A naturally occurring radioactive gas that seeps up from underlying rock and soil through foundation cracks, sump pump openings, and construction joints. The EPA identifies radon as the second leading cause of lung cancer in the US, responsible for an estimated 21,000 deaths per year. It’s odorless and colorless — the only way to know is to test.

Radon varies by geography and by individual home. Two houses on the same street can have dramatically different levels. The EPA recommends mitigation for levels above 4 pCi/L, though some experts argue action should begin at 2 pCi/L.

Mold and Biological Contaminants

Mold spores, mycotoxins, dust mites, pet dander, pollen, and bacteria. Mold is covered extensively in dedicated protocols, but from an air quality perspective: if relative humidity stays above 60% consistently, mold will grow. Period. Behind walls, in HVAC ducts, under carpets, in bathroom ceilings. You may not see it, but your immune system knows it’s there.

Monitoring: Know What You’re Breathing

AirThings Wave Plus (~$230)

Monitors radon (long-term tracking), CO2, total VOCs, temperature, humidity, and air pressure. The radon feature alone justifies the cost — professional radon tests cost $150+ and give you a snapshot, while AirThings gives continuous data.

PurpleAir Sensors (~$230-300)

Real-time PM2.5 monitoring. The outdoor versions also contribute to a public air quality map (purpleair.com), but the indoor versions are what matter for home assessment. Cooking, vacuuming, and candle burning will spike your PM2.5 in real-time — seeing the numbers changes behavior fast.

CO2 Monitoring (~$30-100)

Aranet4 or similar CO2 monitors. Indoor CO2 above 1,000 ppm indicates poor ventilation and is associated with cognitive impairment. A Harvard study (Allen et al., 2016, published in Environmental Health Perspectives) found that cognitive function scores were 61% higher in green buildings with enhanced ventilation compared to conventional buildings. CO2 is the proxy measure for ventilation adequacy.

Carbon Monoxide Detectors

These are non-negotiable in any home with gas appliances, fireplaces, or attached garages. Low-level CO monitors (like the Forensics Detectors or CO Experts models) detect chronic low-level exposure that standard alarms miss — they only trigger at acutely dangerous levels.

Air Filtration Systems

HEPA Filtration

True HEPA filters capture 99.97% of particles at 0.3 microns — the most penetrating particle size. Larger and smaller particles are actually caught more efficiently. HEPA handles dust, mold spores, pollen, pet dander, bacteria, and some virus-containing droplets.

What HEPA doesn’t remove: gases, VOCs, formaldehyde, CO, radon, or odors. For chemical pollutants, you need activated carbon.

Activated Carbon

Adsorbs gases, VOCs, and many chemical pollutants. The more carbon, the better — cheap air purifiers with a thin carbon sheet do very little. Quality units use 5-15 pounds of granular activated carbon. Some use specialty carbon treated with potassium iodide or permanganate for formaldehyde and specific chemicals.

Recommended Air Purifiers

• Austin Air HealthMate Plus (~$715): 60 sq ft of medical-grade HEPA + 15 lbs of activated carbon with zeolite. The gold standard for combined particle and chemical filtration. Designed for chemically sensitive individuals.
• IQAir HealthPro Plus (~$900): HyperHEPA technology that captures particles down to 0.003 microns — 100x smaller than standard HEPA. Exceptional for ultrafine particles but less carbon capacity.
• Blueair Classic series (~$300-700): excellent CADR (Clean Air Delivery Rate) for the price, HEPASilent technology combines mechanical and electrostatic filtration.

HVAC Filtration

If you have central air, your return air filter is your whole-house air cleaner — or your whole-house recirculator of junk. Standard fiberglass filters (MERV 1-4) catch essentially nothing of biological significance. Upgrade to MERV 13 minimum — this captures 85%+ of particles 1-3 microns. MERV 16 approaches HEPA territory. Check that your HVAC system can handle the increased airflow resistance; a filter too restrictive for the system will reduce airflow and strain the blower motor.

Change HVAC filters on schedule. A dirty filter is worse than a thin one — it becomes a mold breeding ground and particulate source.

Natural Air Purification

Houseplants

NASA’s Clean Air Study (Wolverton et al., 1989) found that certain houseplants remove specific VOCs from sealed chambers:

• Peace lily (Spathiphyllum): benzene, formaldehyde, trichloroethylene, ammonia
• Spider plant (Chlorophytum comosum): formaldehyde, xylene
• Snake plant (Sansevia): benzene, formaldehyde, trichloroethylene, xylene — and it releases oxygen at night (unlike most plants)
• English ivy: formaldehyde, benzene, particularly effective for airborne fecal particles
• Boston fern: formaldehyde, xylene

The reality check: subsequent research (Cummings & Waring, 2019, in Journal of Exposure Science & Environmental Epidemiology) calculated that you would need 10-1,000 plants per square meter to match the air cleaning rate of moderate ventilation. Plants are beneficial for humidity, psychological wellbeing, and marginal air quality improvement — but they are not a replacement for mechanical filtration and ventilation.

Ventilation: The Forgotten Strategy

The Tight Building Problem

Modern construction prioritizes energy efficiency — tight building envelopes, sealed ductwork, minimal air infiltration. This is great for energy bills and terrible for air quality. An older, drafty house may have air exchange rates of 1-2 air changes per hour (ACH). A modern tight house might achieve 0.1-0.3 ACH. Everything that off-gasses, every breath of CO2, every cooking emission just accumulates.

ERV and HRV Units

Energy Recovery Ventilators (ERV) and Heat Recovery Ventilators (HRV) solve this by exchanging stale indoor air for fresh outdoor air while recovering 70-80% of the heating or cooling energy. An HRV is preferred in cold climates; an ERV in humid climates (it also transfers moisture, preventing over-drying in winter and excessive humidity in summer). Cost: $1,000-3,000 installed for a quality unit (Zehnder, Broan, Panasonic).

Strategic Window Opening

When outdoor air quality is good (check AirNow.gov or your PurpleAir map), opening windows on opposite sides of the home creates cross-ventilation. Even 15-30 minutes of open-window cross-ventilation dramatically reduces indoor CO2 and VOC concentrations. Avoid opening windows during high pollen, wildfire smoke, or heavy traffic periods.

CO2 as Your Guide

Keep a CO2 monitor visible. When it climbs above 800-1,000 ppm, increase ventilation. Bedrooms are notorious CO2 traps — a closed bedroom with two adults will reach 2,000+ ppm by morning. Crack the door, run a ceiling fan, or install a dedicated bedroom ERV.

Combustion Sources

Gas Stoves

The Lebel et al. 2022 study published in Environmental Science & Technology found that gas stoves emit nitrogen dioxide (NO2) at levels that frequently exceed EPA outdoor air quality standards inside the home — particularly in smaller kitchens with poor ventilation. A meta-analysis by Gruenwald et al. (2023) associated gas stove use with a 12.7% increase in childhood asthma risk. Gas stoves also emit benzene, formaldehyde, and ultrafine particles during combustion.

Mitigation: always use the range hood (vented to outdoors, not recirculating), open a window during cooking, or consider switching to induction (which produces zero combustion emissions and is also faster and more energy-efficient).

Fireplaces and Wood Stoves

Wood burning produces massive PM2.5, polycyclic aromatic hydrocarbons (PAHs), benzene, formaldehyde, and carbon monoxide. An evening fire can elevate indoor PM2.5 to levels comparable to a polluted city day. If you love a fireplace, use EPA-certified wood stoves (they burn 70% cleaner than old open fireplaces) and ensure proper chimney draw.

Candles and Incense

Paraffin candles (petroleum-derived) emit toluene, benzene, and soot. Incense smoke contains PAHs at concentrations exceeding cigarette smoke in some studies. If you enjoy candles, switch to beeswax or soy with cotton wicks — they produce minimal soot and no petroleum byproducts.

Building Materials and Furnishings

Choosing Low-Toxicity Materials

• Paint: zero-VOC paints (Benjamin Moore Natura, Sherwin-Williams Harmony, AFM Safecoat) emit virtually no VOCs during or after application
• Flooring: solid hardwood, ceramic tile, natural stone, or cork are inherently low-emission. Avoid laminate (formaldehyde-based adhesive), vinyl/LVP (phthalates), and wall-to-wall carpet (VOC off-gassing + dust/allergen/mold trap)
• Furniture: solid wood with natural oil finishes vs. pressed-wood with formaldehyde-laden particle board. Off-gas new furniture in a garage or well-ventilated room for 2-4 weeks before bringing it into living spaces
• Mattresses: see the bedroom detox protocol — flame retardants and polyurethane foam off-gassing are major bedroom air quality issues

Carpet: The Indoor Pollutant Reservoir

Wall-to-wall carpet is a functional medicine red flag. It traps dust mites, mold spores, pet dander, pesticide residue tracked in on shoes, and heavy metals from household dust. New carpet off-gasses 4-PC (the “new carpet smell”), formaldehyde, and dozens of other VOCs. Carpet cannot be truly cleaned — vacuuming recovers surface debris but leaves deep contamination. The healthiest floor covering for air quality: hard surfaces (tile, hardwood, concrete) with washable area rugs.

Radon Mitigation

If testing reveals radon above 4 pCi/L (and consider acting above 2 pCi/L):

• Sub-slab depressurization: the standard fix. A pipe is installed through the foundation slab, connected to a fan that draws radon from beneath the house and vents it above the roofline. Cost: $800-2,500. Highly effective — typically reduces levels by 80-99%.
• Sealing foundation cracks: reduces entry points but rarely sufficient alone
• Improved ventilation: dilutes radon but doesn’t eliminate it

Test again after mitigation to verify effectiveness. Radon levels can change over time with geological shifts, so periodic retesting (every 2-5 years) is wise.

The Integration Point

Air quality connects to every system functional medicine cares about. Chronic low-level chemical exposure (VOCs, combustion gases) taxes the liver’s detoxification capacity. Particulate matter drives systemic inflammation. Mold spores trigger immune dysregulation. CO2 accumulation impairs cognition. Radon damages DNA.

The interventions are straightforward but rarely implemented because the problem is invisible. A $200 air quality monitor and a $300 air purifier can transform your health trajectory more than many expensive supplements. The body has tremendous healing capacity — but not when it’s being assaulted 20,000 breaths a day by the very air inside its sanctuary.

When was the last time you thought about the quality of the air you’re breathing right now?