Improve Indoor Air Quality

Why: The EPA says ozone is a toxic gas that can damage the lungs and worsen asthma, and that at levels within health standards ozone has little potential to remove indoor contaminants. It does not remove particles, allergens, carbon monoxide or formaldehyde, and can create irritating byproducts. No federal agency has approved these devices for occupied spaces.

Who it applies to: Anyone, especially people with asthma and children.

Try instead: Use source control, ventilation and a particle filter that does not make ozone. The EPA says electrostatic precipitators, ionizers and plasma units may also make ozone, and lists low-ozone testing programs.

Why: Unvented gas heaters, charcoal, generators and camp stoves can produce carbon monoxide and nitrogen dioxide. The CDC says never heat your house with a gas oven, never use a generator inside the home or garage even with doors open, never burn charcoal indoors and never run a car in an attached garage.

Who it applies to: Everyone, especially during cold weather and power cuts.

Try instead: Use properly installed, vented, serviced appliances and keep generators more than 20 feet from windows, doors and vents.

Why: The EPA lists tobacco products and secondhand smoke among indoor pollutants and advises avoiding indoor smoking and vaping during smoke events. We did not find a figure for vaping aerosol in the sources we read, so no precise risk is stated here.

Who it applies to: Anyone who shares indoor space with a smoker, especially children and people with asthma.

Try instead: Keep homes and cars smoke-free and use support to quit.

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Why: Dampness or mold is consistently associated with asthma flare-ups, wheeze, cough and respiratory infections, and the EPA says mold can irritate even people who are not allergic.

Who it applies to: People with asthma, allergies, babies and older adults.

Try instead: Find and fix the water source, dry affected items, and keep humidity moderate.

Why: Gas stoves are an indoor source of nitrogen dioxide, which the EPA says can irritate and increases bronchial reactivity in some people with asthma. Cooking also creates short-term spikes in pollutants.

Who it applies to: Children, people with asthma and households with small, closed kitchens.

Try instead: Use a vented hood or fan, and open a window while cooking.

Why: The EPA lists burning candles or incense, frying or broiling, and using gas or wood stoves among activities that add indoor particles during smoke events. We did not find an agency source we read that measures their effect on health at other times.

Who it applies to: People with asthma, heart or lung disease during smoky days.

Try instead: Limit them when air is already poor, and ventilate when you do use them.

Why: The EPA lists air fresheners and aerosol products among sources of volatile organic compounds that can irritate the airways and cause headaches.

Who it applies to: People with asthma, fragrance sensitivity and those who clean in small spaces.

Try instead: Choose fragrance-free products where you can and ventilate when you use any.

Why: The EPA says plasma, photocatalytic oxidation and UV have not been shown to remove gases effectively in residential units, and some ionizing devices can produce ozone. The EPA does not certify or endorse specific brands.

Who it applies to: Shoppers comparing devices.

Try instead: Prefer a particle filter with a clean air delivery rate that suits the room, and check low-ozone lists.

Why: The EPA says most table-top models remove particles poorly, and air cleaners generally do not remove gases or reduce radon.

Who it applies to: Anyone relying on a small unit in a large room.

Try instead: Size the unit by clean air delivery rate for the room and keep filters fresh.

Why: The EPA says to clean portable humidifiers every third day and use low-mineral water, and that high humidity may encourage growth of biological organisms.

Who it applies to: Households with asthma or allergy.

Try instead: Clean on schedule, use distilled water and keep humidity at or below 50 percent.

Why: Chamber studies do not translate to homes: a review concluded 10 to 1,000 plants per square meter would be needed to match normal air exchange.

Who it applies to: Social media and décor sites.

Try instead: Use ventilation and source control for air quality.

Why: The EPA says levels needed to kill biological contaminants would be 5 to 10 times above health standards, and ozone does not remove embedded contaminants.

Who it applies to: Sellers of ozone machines.

Try instead: Fix moisture and remove mold physically.

Why: Trials have given small or inconsistent results. One blinded trial in schools found no significant reduction in asthma symptom-days, and a home trial's main outcome was not significant.

Who it applies to: Product advertising.

Try instead: Use air cleaning as a supplement and keep taking and following your prescribed plan.

Why: The EPA says testing is usually unnecessary when mold is visible, and that no federal limits exist for mold or spores. A review found current evidence does not support measuring specific microbiologic factors to guide actions.

Who it applies to: Anyone who finds mold.

Try instead: Find and fix the source of moisture and clean up the mold.

Why: The CDC advises checking batteries when the clocks change and replacing detectors per instructions or every 5 years.

Who it applies to: Every home with fuel-burning appliances.

Try instead: Put a reminder in your calendar and test regularly.

Why: Radon has no smell or sign. The EPA says average indoor levels are 1.3 pCi/L and urges testing.

Who it applies to: Every home.

Try instead: Test once, and again after major changes such as renovations.

A review of chamber studies concluded plants would be needed in the thousands to match normal air exchange, and the EPA finds no evidence that a reasonable number meaningfully reduce pollutants.

The EPA says ozone can harm the lungs and has little ability to remove indoor contaminants at safe levels, and no federal agency has approved the devices for occupied spaces.

A small randomized trial showed mixed results, and a larger blinded school trial found no significant reduction in symptom-days. Air cleaners may help some people but are not proven treatment.

The EPA says testing is usually unnecessary when mold is visible, and a review does not support measuring microbiologic factors to guide action.

A meta-analysis of 41 studies found gas cooking was associated with higher odds of childhood asthma (odds ratio 1.32). This shows association, and vented hoods are the EPA's advised response.

No: the NHS says it is colourless and odourless, so alarms matter.