Why indoor air matters more than outdoor air.
You track your steps, filter your water, and read labels on the food you buy. But the one exposure you cannot opt out of is the air you breathe roughly 20,000 times a day, and for most families, it has never been tested.
We spend about 90 percent of our lives indoors. The air inside a typical home is two to five times more polluted than the air outside, according to the US Environmental Protection Agency. In Los Angeles, the problem compounds: outdoor ozone and wildfire smoke push homeowners to keep windows closed, and a sealed home with an under-maintained HVAC system simply recirculates and concentrates whatever is already inside.
Exposure is concentration multiplied by time. You do not need a dramatically high reading to be affected. Years of steady, low-level exposure to the wrong things can cause real, measurable harm. That is exactly why measuring matters.
What's actually in the air, and what it does to the body.
Each of the pollutants below affects the body through different pathways. Some hit the lungs first. Others pass through the lungs and damage the heart and blood vessels. Different family members will care about different columns.
Cooking, candles, wildfire smoke, HVAC dust, gas combustion, nearby traffic.
Coughing, wheezing, shortness of breath, chest tightness, eye and throat irritation, fatigue, and more frequent colds or respiratory infections.
Penetrates deep into the lungs. Triggers and worsens asthma, COPD, chronic bronchitis, and emphysema. Reduces lung development in children. Linked to lung cancer and more frequent respiratory infections.
Long-term exposure is strongly linked to heart attack, stroke, high blood pressure, and irregular heart rhythms (American Heart Association).
Also associated with low birth weight, preterm delivery, and cognitive decline in older adults.
Gas stoves, unvented gas heaters, attached garages, nearby traffic.
Coughing, wheezing, shortness of breath, chest tightness, more frequent asthma flares, reduced exercise tolerance, and repeated respiratory infections — often worse in kitchens with gas cooking.
Directly constricts airways. Contributes to new-onset and worsened asthma, especially in children, and worsens COPD and chronic bronchitis. Increases susceptibility to respiratory infection.
Contributes to inflammation of blood vessels and is associated with increased cardiovascular hospitalizations.
Gas stove use is linked to a meaningful share of childhood asthma cases (Gruenwald et al., 2022).
Flooring, cabinetry, paints, fragrance in cleaners and candles, new furniture, recent remodels.
Headaches, dizziness, watery or burning eyes, sore throat, runny nose, nausea, skin rash, fatigue, and worsened asthma — especially after remodels or when new furniture or flooring is introduced.
Irritates the airways. Triggers asthma and reactive airway symptoms. Chronic exposure can reduce lung function.
Some VOCs, including benzene and 1,3-butadiene, are associated with cardiovascular disease at chronic exposure.
Formaldehyde and benzene are classified as known human carcinogens (leukemia, nasopharyngeal cancer). Headaches, eye and throat irritation, and fatigue are common early signs.
People exhaling in rooms with poor ventilation.
Morning grogginess, headaches, drowsiness, difficulty concentrating, a persistent "stuffy room" feeling, restlessness, and poor sleep quality — especially in bedrooms with closed doors overnight.
Not directly toxic at residential levels, but it is the best single indicator of poor ventilation. Where CO₂ is high, every other pollutant is also accumulating.
Chronically elevated levels can contribute to fatigue and cardiovascular strain over time.
Elevated CO₂ is associated with reduced cognitive performance and poorer sleep quality in controlled studies. Morning grogginess and headaches are common signs.
Gas ranges, water heaters, attached garages, aging furnaces.
Headache, dizziness, nausea, weakness, blurred vision, confusion, and chest pain in anyone with heart disease. Higher exposure causes loss of consciousness. Symptoms often improve quickly once you leave the home — a key warning sign.
Not a direct lung irritant, but it displaces oxygen in the blood. Particularly dangerous for anyone with COPD, asthma, or any condition that reduces lung capacity.
Binds to hemoglobin more than 200 times more readily than oxygen. Chronic low-level exposure is linked to angina, arrhythmia, and heart attack, especially in people with existing heart disease.
Standard residential CO detectors often only alarm at levels that are already dangerous. Acute symptoms include headache, confusion, and loss of consciousness.
Seeps through foundations and slabs from the soil below.
None. Radon is colorless, odorless, and tasteless, and causes no symptoms until lung cancer develops years later. A measurement is the only way to know your exposure.
Second leading cause of lung cancer in the United States, responsible for an estimated 21,000 deaths per year (EPA). The risk is dramatically higher in anyone with any smoking history, because the effects compound rather than simply add.
No direct effect on the heart or circulation.
Colorless, odorless, and tasteless. There are no symptoms until disease appears. The only way to know is to measure, and the measurement has to be done correctly.
HVAC, leaks, climate, building envelope.
Too dry (<30%): dry or cracked skin, nosebleeds, sore throat, scratchy eyes, static shocks, and worsened asthma or sinusitis. Too humid (>50%): musty smell, clammy feeling, allergy-like congestion, headaches, and fatigue from mold and dust mite growth.
Below 30%: dries airways, worsens asthma, sinusitis, and respiratory infection susceptibility. Above 50%: drives mold, dust mites, and bacteria — triggers for asthma, chronic bronchitis, allergic rhinitis, and sinusitis.
High humidity adds strain through thermoregulation. Very dry air can thicken blood and is associated with increased cardiac events in winter months.
Also affects skin, sleep, wood floors, and furniture.
Moisture intrusion, roof and plumbing leaks, HVAC condensate, crawlspaces.
Persistent congestion, sneezing, runny nose, itchy or watery eyes, cough, wheezing, sinus pressure, headaches, skin irritation, and "brain fog" or fatigue that improves when you're away from home.
Strong trigger for asthma, COPD exacerbation, allergic rhinitis, chronic sinusitis, and hypersensitivity pneumonitis. Chronic exposure is linked to new-onset asthma in children and accelerated lung function decline.
Chronic inflammation from mold exposure may contribute to cardiovascular strain in sensitive individuals.
Brain fog, fatigue, and immune symptoms are commonly reported.
Tobacco, cannabis, and e-cigarette use indoors, including residue on surfaces ("third-hand smoke").
Coughing, wheezing, throat and eye irritation, headaches, and more frequent ear and respiratory infections — especially in children. Worsened asthma control and reduced exercise tolerance are common.
Causes and worsens asthma, COPD, chronic bronchitis, lung cancer, and respiratory infections in non-smokers. There is no safe level of exposure, especially for children.
Strongly linked to heart disease, heart attack, and stroke in non-smoking household members.
Residue on walls, carpets, and furniture continues to release toxins for months after smoking stops.
Cats, dogs, dust mites in bedding and carpet, cockroach and rodent residue.
Sneezing, runny or stuffy nose, itchy or watery eyes, post-nasal drip, coughing, wheezing, eczema flares, and night waking from congestion — often worse in bedrooms and on carpeted floors.
Common triggers for asthma, allergic rhinitis, and eczema-related airway symptoms. Recognized by the CDC as leading causes of pediatric asthma exacerbation.
Not direct, but chronic allergic inflammation is increasingly linked to broader systemic effects.
Pest allergens are frequently found in homes where no live pests are visible.
Things a Baseline assessment does not measure
An IAQ assessment is focused on air. A few health-relevant home hazards live outside that scope. If any apply to your home, we can refer you to a qualified specialist.
- Asbestos — common in homes built before 1980. Requires a specialized inspection.
- Lead paint and lead dust — common in homes built before 1978. Requires a certified lead assessor.
- Legionella — from water systems, humidifiers, and decorative fountains. Requires water testing.
What "normal" actually looks like.
These are the ranges a professional assessment compares your home against. They are drawn from EPA, WHO, and American Lung Association guidance.
| Measurement | Healthy Range |
|---|---|
| PM2.5 | < 9.0 μg/m³ annual avg (EPA 2024) |
| Total VOCs | < 220 μg/m³ |
| CO₂ | < 800 ppm |
| Carbon Monoxide | < 9 ppm (8-hr avg) |
| Relative Humidity | 40 to 60% |
| Temperature | 68 to 76°F |
| Radon | < 4 pCi/L (EPA action level) |
Who needs to take these findings most seriously.
Everyone benefits from cleaner indoor air, but certain people are significantly more vulnerable to the effects of poor air and should weight an assessment accordingly.
- Anyone with a respiratory condition — asthma, COPD, chronic bronchitis, emphysema, cystic fibrosis, long COVID lung involvement, or recent serious respiratory illness.
- Anyone with a heart or circulatory condition — coronary artery disease, heart failure, prior heart attack or stroke, high blood pressure, or irregular heart rhythm.
- Anyone with a smoking history, past or present — especially relevant for radon, where the risk is dramatically amplified.
- Children — lungs continue developing through adolescence, and early exposure to PM2.5 and NO₂ causes effects that do not fully reverse.
- Pregnant women — PM2.5 is linked to low birth weight and preterm delivery.
- Older adults — less pulmonary and cardiovascular reserve to absorb the effects of poor air.
- Immunocompromised household members — higher vulnerability to mold, bacteria, and respiratory infections.
Signs your home's air may be affecting your family.
Any one of these can have other explanations. But if two or more are present, your home's air quality deserves to be ruled out, not assumed to be fine.
- Morning headaches or grogginess that fade after leaving home
- Congestion or runny nose that clears up when you're away
- Family members sleeping poorly without obvious cause
- Pets showing lethargy or unusual respiratory symptoms
- Persistent musty or chemical smell you've stopped noticing
- Allergy-like symptoms outside of allergy season
- Difficulty concentrating at home vs. elsewhere
- Recent remodel, new flooring, or new furniture
- Older HVAC system or infrequent filter changes
- Home built before 1990 with basement, crawlspace, or slab
What actually helps, in order of impact.
Not all interventions are equally effective, and some popular products can make your air worse. These are the things with real evidence behind them.
Things to avoid
- Ozone-generating "air purifiers" — ozone is a respiratory irritant and the EPA specifically warns against these devices.
- Ionizer and "plasma" purifiers without independent testing — many produce ozone or ultrafine particles as byproducts.
- Scented candles and plug-in air fresheners marketed as "air purifying" — they add VOCs rather than remove them.
- Short hardware-store radon tests for homes with a crawlspace, basement, or raised foundation — the result is not reliable enough to act on.
Get the companion IAQ Action Guide.
You've read what's actually in your air. The Action Guide is the practical companion — filter upgrades, ventilation fixes, humidity targets, and the specific steps that move the numbers on each of the pollutants above. Sent straight to your inbox, free.
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Schedule Your AssessmentThis guide is for informational purposes only and is not medical advice. It does not diagnose or treat any health condition. If you or a family member has symptoms or a diagnosed condition, please consult a licensed healthcare provider. Baseline Home is an indoor air quality assessment service and does not provide medical care.
Sources: US Environmental Protection Agency, American Lung Association, World Health Organization, American Heart Association, Centers for Disease Control and Prevention.