What doesn't work
A whole category of home-environment products sells the feeling of a fix without the function.
Save your money
Some do nothing; a few make the air worse. The pattern repeats: a device claims to destroy or neutralize a pollutant, the marketing leads with a science-flavored mechanism, and the independent evidence never shows up. The test that sorts the real from the theater is below.
Ionizers and 'plasma' air purifiers
Can make it worse
The claim Charged ions make airborne particles clump and drop out, cleaning the air without a filter.
What the evidence shows Independent evidence for real-world particle removal is weak, and many ionizers emit ozone as a byproduct. Ozone is itself a lung irritant and a smog gas, so the device can trade a particle problem for a gas problem. A true HEPA filter does the particle job without making ozone.
Ozone generators sold as 'air cleaners'
Can make it worse
The claim Ozone oxidizes pollutants, odors, and mold, sanitizing a room's air.
What the evidence shows The EPA's position is that ozone has little ability to remove indoor contaminants at concentrations that are safe to breathe, and ozone is a respiratory hazard in its own right. California banned the sale of indoor ozone-generating air cleaners (ARB regulation, effective 2010). Never run one in occupied space.
PCO / PECO photocatalytic purifiers
Can make it worse
The claim A light-activated catalyst breaks pollutants down into harmless molecules.
What the evidence shows In testing, photocatalytic oxidation can generate new byproducts, including formaldehyde and acetaldehyde, rather than cleanly destroying what was there. One prominent brand settled a false-advertising class action in 2022. The work on particles is still done by a plain filter, on gases by activated carbon.
Houseplants as an air purifier
Too small to matter
The claim A few potted plants clean the air, the way the old NASA study suggested.
What the evidence shows That study was a sealed-chamber experiment, and scaling it to a real room collapses. A 2020 analysis (Cummings and Waring) found you would need on the order of hundreds of plants in a normal-sized home to match the air cleaning of simply opening one window. Keep plants because you like them. Do not count them as filtration.
Salt lamps, charcoal bags, and 'air-purifying' gadgets
Does not work
The claim Himalayan salt lamps, bamboo charcoal bags, and similar passive objects purify or ionize room air.
What the evidence shows None show meaningful particle removal in residential conditions. Passive charcoal has a trivial surface area next to a real activated-carbon filter, and salt lamps are decorative. They change nothing measurable about what you breathe.
Blue-light blocking glasses for daytime wear
Unproven
The claim Blue-blocking lenses reduce eye strain and protect your health from screens.
What the evidence shows The American Academy of Ophthalmology finds no evidence that blue-light glasses help eye strain or eye health for general daytime use. What matters for sleep is dim, warm light in the evening, and your phone's built-in night mode does the screen part for free.
American Academy of Ophthalmology, position on blue-light glasses
'Hypoallergenic' cat and dog breeds
Misleading claim
The claim Certain breeds produce less allergen, so an allergic household can keep a pet safely.
What the evidence shows Two studies measuring actual allergen in homes (Vredegoor 2012 across nearly 200 'hypoallergenic' dogs; Nicholas 2011 across 173 homes) found no meaningful reduction, and the 'hypoallergenic' samples sometimes carried more. All cats and dogs produce the major allergens. Hypoallergenic is a marketing category.
Vredegoor et al., 2012 (J Allergy Clin Immunol); Nicholas et al., 2011 (Am J Rhinol Allergy)
Sealing cracks alone to fix radon
Not enough alone
The claim Caulking foundation cracks and slab penetrations lowers a home's radon level.
What the evidence shows The EPA states plainly that sealing by itself has not been shown to reduce radon significantly or consistently. Sealing is one step inside a proper radon-reduction system that uses a fan to pull radon out from under the slab. A handyman caulk job that gets called 'fixed' usually is not.
Essential-oil diffusers used as humidifiers
Can make it worse
The claim Add essential oils to the humidifier tank for scented, healthier moist air.
What the evidence shows Oil floating on the water reduces moisture output and leaves a residue that feeds microbial growth in the tank. Use a humidifier for humidity and a separate method for scent. The two jobs do not belong in the same reservoir.
'Germ-free' UV-in-tank humidifier features
Misleading claim
The claim A UV light in the tank kills bacteria, making the humidifier germ-free.
What the evidence shows The wick and the biofilm sit outside the light path, so the UV lamp does not reach where the growth happens. Daily emptying, regular cleaning, and routine wick replacement are what keep a humidifier clean. The UV feature does not remove that maintenance.
'Zero-VOC' and 'low-VOC' product labels
Misleading claim
The claim A zero-VOC paint or product means nothing harmful off-gasses into your home.
What the evidence shows The regulatory VOC count exists to limit smog, and it legally excludes dozens of compounds that do not form ground-level ozone but still off-gas indoors. A 'zero-VOC' label can sit on a product that emits exempt solvents. Health-based certifications like Greenguard Gold and CDPH 01350 test every emitted compound. The marketing label does not.
SCAQMD Rule 1113 exempt-compound advisory; EPA 40 CFR 51.100(s)
TVOC-number gadgets read as a safety score
Misleading claim
The claim A consumer air monitor's total-VOC number tells you whether your air is safe.
What the evidence shows A consumer TVOC sensor reports a relative index, not a health threshold, and it cannot tell one compound from another. It is useful for spotting when a source is active, like cooking, painting, or cleaning, and useless as a pass-fail safety reading. Use it to track changes over time, not as a single number.
Salt-free 'softeners' sold as water softeners
Misleading claim
The claim A no-salt 'conditioner' softens your water without the maintenance of a salt system.
What the evidence shows These devices alter how minerals crystallize to cut scale, but they do not remove the calcium and magnesium, so the water is never truly softened. A conditioner is a scale-reduction device. Sold as a 'softener,' the device borrows a word for work it does not do.
What to do instead
One test sorts most of these: ask what independent body has measured the device against the pollutant it claims to fix, and at what concentration. A real fix names its mechanism in plain physics, removes the thing rather than 'neutralizing' or 'energizing' it, and survives third-party testing.
If the pitch leans on a science-flavored word with no measured reduction behind it, or if the device makes a new byproduct (ozone is the common one), treat the claim as marketing. The reason these persist is that doing nothing visible feels like doing nothing, and a glowing box on the counter feels like action.
The moves that work are unglamorous: filter particles with HEPA, remove gases with enough activated carbon, fix radon with depressurization, fix moisture at the source, and open a window for fresh air.
Common questions about What doesn't work
Are ionizers and ozone air purifiers safe?
No, not for occupied rooms. Both can release ozone, which irritates the lungs and is itself an air pollutant. California banned the sale of indoor ozone-generating air cleaners in 2010, and the EPA says ozone does not clean indoor air at concentrations that are safe to breathe. A true HEPA filter handles particles without producing any gas.
Do houseplants actually clean indoor air?
Not at any meaningful scale. The famous NASA result came from a sealed chamber. In a real room you would need hundreds of plants to match the air exchange of opening a single window (Cummings and Waring, 2020). Keep plants because you like them, and let a filter do the filtering.
Is a 'zero-VOC' paint label trustworthy?
Not on its own. The VOC count is a smog-control measure and legally excludes many compounds that still off-gas indoors, so a 'zero-VOC' product can still emit exempt solvents. Look for a health-based certification like Greenguard Gold or CDPH 01350, which tests every emitted compound rather than only the regulated ones.
Will sealing cracks fix my radon problem?
No, not by itself. The EPA states that sealing alone has not been shown to lower radon significantly or consistently. Sealing is one part of a proper sub-slab depressurization system, the fan-driven approach that pulls radon out from under the slab. A caulk-only 'fix' is not enough.
Are hypoallergenic dog and cat breeds real?
Not in any measured sense. Studies that sampled allergen in real homes found no meaningful difference, and some 'hypoallergenic' samples carried more. All cats and dogs produce the major allergens. If someone in the home is allergic, manage exposure with HEPA filtration, keeping the pet out of the bedroom, and humidity control rather than relying on the breed label.
Sources cited for What doesn't work
Every number on this method page traces to one of the 6 sources below: 2 peer-reviewed, 3 government or regulatory.
Peer-reviewed
Government & regulatory
Institutional & standards
Related home science
- Guide Do I need an air purifier? An air purifier helps if your problem is airborne particles: cooking smoke, wildfire haze, traffic soot, pollen, or pet dander.
- Guide Do I need a water filter? For most US homes, yes.
- Guide I found mold. How bad is it? A small patch you can see and reach is usually a homeowner job, not an emergency.
- Topic PM2.5 (fine particulate matter) PM2.5 means particulate matter 2.5 micrometers across or smaller.
- Topic VOCs and formaldehyde VOCs, volatile organic compounds, are carbon-based chemicals that evaporate at normal room temperature, so they leave their source and become a gas you breathe.
- Topic Smog (ozone + NO2) Smog is two pollutants that travel together.
- Topic Radon Radon-222 is a colorless, odorless, radioactive gas formed as uranium in soil and rock slowly decays.
- Topic Allergens (dust mite, pet, pollen) Three biological exposures share your home.
- Topic Indoor humidity Humidity is water vapor in air.
- Topic Water hardness Hardness is the amount of dissolved calcium and magnesium in water, reported as milligrams per liter of calcium carbonate equivalent (mg/L as CaCO3) or, on the consumer scale, in grains per gallon.
- Topic Indoor lighting Light is information before it is brightness.