Don’t take our word for it. Here’s every fact on this site, with its evidence grade, its caveats, and a link to the source, so you can check us.
We start you on the strong ones: findings that have been replicated or come from one large, well-controlled study. Moderate and weak facts are here too, labeled for what they are. Use “Link to this fact” to share a single card.
Indoor air / Measured in people or real products
Scented laundry products put fragrance chemicals into outdoor air: in two homes, limonene (a citrus scent chemical) came out of the dryer vent only when fragranced detergent or dryer sheets were used (up to 14.7 ug/m3), not in the no-product runs.
Moderate evidence.
Caveats
2 homes (Steinemann 2013), single grab samples; undiluted vent air, not a breathing-zone dose. Replicated at much higher magnitude and with a dose-response signal by Goodman et al. 2019 (6 Melbourne homes, before/after switch design): fragranced-detergent vent D-limonene 2.35-118 ug/m3 vs 0.24-0.26 ug/m3 in fragrance-free-only homes, and switching from fragranced to fragrance-free detergent cut vent D-limonene by up to 99.7% (mean 79.1%) within a month. The two studies share one author (Anne Steinemann) and neither ran statistical significance tests, so the combined evidence (8 homes total) stays below strong, but the qualitative and dose-response finding is now cross-country replicated within one research program rather than resting on a single 2-home study.
Source: Steinemann 2013, Air Quality, Atmosphere & Health Link to this fact
Indoor air / Measured in people or real products
Scent chemicals in cleaners and air fresheners react with ozone that drifts in from outdoors to make formaldehyde: cleaning raised formaldehyde by 9-16 ppb for 4 hours, and a plug-in air freshener raised it by about 6 ppb for as long as it ran.
Moderate evidence.
Caveats
Secondary formation only, depends on indoor ozone. The underlying mechanism is now directly quantified at bench scale (Destaillats 2006: formaldehyde 16-38% per ozone consumed for the same three products), but that bench study is the same research group/products/contract as this one, not an independent replication, so the grade is not raised on that basis alone.
Source: Singer 2006, Atmospheric Environment Link to this fact
Indoor air / Measured in people or real products
After 2-7 minutes of cleaning with a terpene cleaner, indoor air chemistry stayed altered for 10-12 hours because the scent chemicals soaked into walls and floors and came back out.
Moderate evidence.
Caveats
Empty chamber; furnished rooms may differ. Singer 2006 (Indoor Air primary-emissions companion, same 50 m3 room without ozone) corroborates the sorption/desorption mechanism directly: alpha-terpineol stays at 260-700 ug/m3 for hours and ~90 ug/m3 at 4-24 h via surface water films and wallboard sorption, and towels left in the room raise 24-h emissions 35-100%. Not independent (same lab/room/products as the ozone paper).
Source: Singer 2006, Atmospheric Environment Link to this fact
Indoor air / Measured in people or real products
In a European study that measured the air 182 adults actually breathed over 48 hours, exposure to pine- and citrus-type scent chemicals from cleaning products and fragrances rose with the number of children at home (3-carene median 0.9 to 2.5 µg/m³); the authors attribute this to more cleaning.
Moderate evidence: Late-1990s, small subgroups, attribution to cleaning is the authors' inference; CEFIC-LRI co-funded.
Source: Edwards 2006, Atmospheric Environment Industry-funded Link to this fact
Indoor air / Measured in people or real products
Keeping a gel air freshener in a car raised the fragrance chemical limonene in the air the driver breathed 3.6-4.7 times, to about 19-28 ug/m3, during real commutes (10 cars tested).
Moderate evidence: N=5 per group, non-randomized; mostly drivers' own products.
Indoor air / Measured in people or real products
In lab tests, gel air fresheners released limonene at up to 1.5 mg per hour, far more than any other chemical measured.
Moderate evidence.
Caveats
Chamber emission rates; products chosen for high limonene (upper end). Singer 2006 (Indoor Air) found the opposite pattern in a different air-freshener type (plug-in scented oil): limonene was a minor emission (39 mg/day) versus non-reactive esters (bornyl acetate 460, benzyl acetate 320 mg/day). 'Limonene dominates' holds for the limonene-selected gels Jo 2008 tested, not for air fresheners generally.
Indoor air / Measured in people or real products
Indoors, vapors from these products run about 7 times higher than outdoors, and include fragrance chemicals such as limonene.
Moderate evidence: Box model checked against indoor measurements.
Indoor air / Measured in people or real products
Mopping a room with a terpene-based (pine- or citrus-type) cleaner caused bursts of tiny new particles, about 100 times the particle count of outdoor air, as the scent chemicals reacted with ozone.
Moderate evidence.
Caveats
One cleaner, one room, one volunteer; particle number, not mass. The ~100x figure is specific to sub-3 nm nanocluster aerosol; a second real classroom mopping event (Morawska 2009, a school, >=5 nm instrument) reached only ~3-7x the outdoor baseline mopping the same class of product, showing the fold-increase depends heavily on the particle-size cutoff of the instrument used.
Indoor air / Measured in people or real products
During mopping with a terpene cleaner, scent chemicals such as limonene and pinene peaked at 280-380 ppb in the room air.
Moderate evidence.
Caveats
Brief peaks; typical home averages 3-7 ppb (EXPOLIS/Gokhale/Sarigiannis) — but Wang 2017 found one heavily fragranced/cleaned UK home's 5-day AVERAGE reached ~258 ppb, within the same order of magnitude as this mopping peak, showing the 'brief peak vs low average' distinction does not hold for the heaviest product-use homes.
Indoor air / Measured in people or real products
Homes painted, refurnished, or re-floored in the previous 6 months had higher levels of indoor chemicals released into the air (including toluene and xylenes) than other homes.
Moderate evidence: Not a fragrance finding.
Source: Maisey 2013, Atmospheric Environment Link to this fact
Indoor air / Review of other studies
The standard week-long air tests used across Europe miss the short spikes of chemicals released after cleaning, which could change the risk picture for eye and airway irritation.
Moderate evidence: Authors' methodological caveat, not a measured result.
Source: Sarigiannis 2011, Environment International Link to this fact
Indoor air / Lab study (cells or chemistry)
In lab chamber tests set up to mimic a room, the citrus scent chemical limonene reacted with ozone in the air to form fine particles carrying reactive oxygen species.
Moderate evidence.
Caveats
Chamber concentrations exceed typical measured indoor exposure by 5-10x. Particle formation is confirmed in a human chamber (Fiedler 2005), but ROS were not measured there and 130 women showed no acute effect; don't pair this claim with 'linked to irritation'. Wolkoff et al. 2008 (now read directly, the true primary behind this line of evidence) is a mouse gas-vs-particle denuder study showing denuded limonene-ozone-reaction ultrafine particles (~9.5-12.0 mg/m3, gas phase >95% removed) cause NO sensory irritation or airflow-limitation effect at all, statistically indistinguishable from clean air — reinforcing, from a different technique (whole-body mouse bioassay vs in-vitro ROS assay), that particle-bound ROS formation should not be equated with a demonstrated health effect.
Indoor air / Lab study (cells or chemistry)
Limonene produced 2 to 11 times more of these reactive particles than alpha-pinene, the pine scent chemical.
Moderate evidence: Chamber comparison only.
Indoor air / Measured in people or real products
Almost everything in a perfume ends up in the air: one perfume released 964 mg of vapor per gram used, mostly alcohol but also about 32 mg per gram of terpene fragrance chemicals.
Moderate evidence: One perfume; emission factors are lower bounds (PTR-MS blind to some compounds).
Source: Wu 2024, Environmental Science & Technology Letters Link to this fact
Indoor air / Measured in people or real products
OH radicals attack almost every organic chemical in indoor air, not only the ~10% that ozone reacts with, and these reactions happen in the air closest to our bodies; the researchers note that many of the resulting products have never been tested for toxicity.
Moderate evidence: No toxicity or health endpoint measured; the 'untested' statement is the authors' assessment.
Indoor air / Journalism
In 2003 Southern California air regulators estimated that household and small-business products, including cleaners, cosmetics, perfume, and room fresheners, released about 108 tons of smog-forming chemicals a day in the Los Angeles region, second only to vehicle tailpipes.
Moderate evidence: Agency inventory relayed by the LA Times; for measured/modeled figures use McDonald 2018 (LA) and Coggon 2021 (NYC 2018: VCPs comparable to vehicle fuels for ozone).
Source: DONTSPRAYCALIFORNIA 2008 (DOJ ADA docket) Link to this fact
Indoor air / Self-reported survey
Among Australians with diagnosed multiple chemical sensitivities, about three in four (77.5%) said a fragranced product had kept them from going somewhere, and about two in three (64.8%) can't or won't use public toilets with air fresheners.
Moderate evidence.
Caveats
N = 71 (95% CI roughly +/-10-12 points); self-report. Independently corroborated in direction (not in magnitude) by a 2020 systematic review of 13 qualitative MCS studies from 4 countries (Driesen 2020), which found 'limited access' to social/occupational settings as a theme in 9/13 studies using different (interview-based, clinic/support-group-recruited) samples — convergent qualitative evidence, not a quantitative replication, so strength stays moderate rather than moving to strong.
Source: Steinemann 2018, Preventive Medicine Reports Link to this fact
Indoor air / Measured in people or real products
When 40 ppb of ozone was added to a room holding a mix of 23 common indoor chemicals, including the citrus and pine scent chemicals limonene and alpha-pinene, formaldehyde tripled (13 to 40 µg/m³), ultrafine particles rose about 18-fold (2,500 to 46,000 per cm³) and particle mass reached 140 µg/m³.
Moderate evidence: Chamber with VOC load ~10x typical buildings; 23-compound office mixture, not a fragranced product; other alkenes also react.
Source: Fiedler 2005, Environmental Health Perspectives Link to this fact
Indoor air / Self-reported survey
Among US adults reporting diagnosed multiple chemical sensitivity, 59% said they could not use a public restroom with an air freshener and 70% had been kept from going somewhere by fragranced products.
Moderate evidence.
Caveats
Self-report; small subgroup (n=145) in one online panel. Independently corroborated in direction (not in magnitude) by a 2020 systematic review of 13 qualitative MCS studies from 4 countries (Driesen 2020), which found 'limited access' to social/occupational settings as a theme in 9/13 studies using different (interview-based, clinic/support-group-recruited) samples — convergent qualitative evidence, not a quantitative replication, so strength stays moderate rather than moving to strong.
Source: Steinemann 2018 (JOEM), Journal of Occupational and Environmental Medicine Link to this fact
Indoor air / Measured in people or real products
With four people in a test room and indoor ozone at about 35 ppb, the chemical reactivity of the air roughly tripled once ozone was added (from about 8–11 to 25–35 per second). Almost all of the increase came from carbonyls made when ozone hit the natural oils on skin, and across the whole study ozone explained 85% of the variation.
Moderate evidence: One chamber (22.5 m³, 3.2 h⁻¹, mixing fans), one ozone level tested on/off; no health endpoint; fragrance-free products used throughout.
Source: Zannoni 2021, Environmental Science & Technology Link to this fact
Indoor air / Measured in people or real products
A dried film of pine-oil cleaner or orange-oil degreaser, with its scent chemicals already evaporated away, still produced formaldehyde and a burst of new particles when later exposed to ozone.
Moderate evidence: Single glass-plate surface test per product in a lab chamber, not tested on real room surfaces (carpet, fabric, furniture).
Source: Destaillats 2006, Environmental Science & Technology Link to this fact
Indoor air / Measured in people or real products
Cleaning with a pine-oil or citrus cleaner raised scent chemicals (limonene, terpinolene, alpha-terpineol) to about 1,000-6,000 ug/m3 for the first hour in a room-sized chamber, and some stayed elevated for many hours afterwards.
Moderate evidence: Empty chamber; one product per formulation; alpha-terpineol's persistence depends on surface water films and towels left in the room.
Source: Singer 2006, Indoor Air, Indoor Air Link to this fact
Indoor air / Measured in people or real products
A plug-in scented-oil air freshener evaporated 1.5 g of product a day and kept its scent chemicals at 30-160 ug/m3 in the room over three days; its two largest emissions were fragrance esters (bornyl and benzyl acetate, 280-410 ug/m3), not the ozone-reactive terpenes usually studied.
Moderate evidence: One plug-in product; a different air-freshener type (e.g. limonene-selected gels, Jo 2008) can be limonene-dominant instead.
Source: Singer 2006, Indoor Air, Indoor Air Link to this fact
Indoor air / Measured in people or real products
Leaving used paper towels in the room after cleaning increased the solvent and scent chemicals released by 35-100%.
Moderate evidence: Measured over 24 h in an empty chamber.
Source: Singer 2006, Indoor Air, Indoor Air Link to this fact
Indoor air / Measured in people or real products
Among 3,411 Czech households with an infant, the most commonly used chemical products were window cleaner (88%), deodorant (82%) and aerosol/hairspray products (74%), not air fresheners, which were the second-least-used of 18 chemical product categories (26%).
Moderate evidence: Self-reported product use frequency, one Central European cohort; product prevalence does not equal exposure dose or emission rate.
Source: Mikeš 2019, Science of the Total Environment Link to this fact
Indoor air / Measured in people or real products
In a study of 25 UK homes using real whole-air canister sampling (not a lab chamber), the scent chemicals D-limonene and alpha-pinene were the single most abundant VOC measured in 94% of homes, regardless of building age, size, or occupancy.
Moderate evidence.
Caveats
N=25 homes (19 London + 6 York), one country; dominance among 8 quantified VOCs, not an absolute-concentration health claim A larger same-lab study (Heeley-Hill 2021, 60 UK homes, daily diaries; Givaudan-funded fieldwork) found cumulative product-use frequency had almost no predictive power for measured VOC levels (R²<0.001), so treat the product-use link as suggestive.
Source: Wang 2017, Environmental Science: Processes & Impacts Link to this fact
Indoor air / Measured in people or real products
In a study of 60 UK homes with real air sampling (not a lab chamber), the VOC found in the highest concentration indoors was n-butane, an aerosol-spray propellant, not a fragrance chemical; it reached a wintertime maximum of 4,630 ug/m3, and aerosol antiperspirant/deodorant was the single most universally used VOC-releasing product, used in all 60 homes.
Moderate evidence: One UK town's panel-recruited cohort (Ashford, Kent); Givaudan-funded (fieldwork), analysis independent at University of York.
Source: Heeley-Hill 2021, Environmental Science: Processes & Impacts Industry-funded Link to this fact
Indoor air / Measured in people or real products
Dryer-vent air carried far more of the citrus-scent chemical D-limonene when households used fragranced laundry detergent (2.35-118 ug/m3, mean 33.34) than when they used fragrance-free detergent (0.13-1.50 ug/m3 after switching; 0.24-0.26 ug/m3 in households that never used fragranced detergent).
Moderate evidence.
Caveats
6 Melbourne-area homes, D-limonene only (not the fuller VOC/HAP panel), no statistical significance testing; shares one author (Anne Steinemann) with the earlier 2-home study it builds on, so not a fully independent replication.
Source: Goodman 2019, Air Quality, Atmosphere & Health Link to this fact
Indoor air / Measured in people or real products
Every one of 25 fragranced laundry products tested (US and Australian detergents and dryer sheets) emitted a terpene fragrance chemical (such as limonene, alpha-pinene, or eucalyptol), while none of 10 fragrance-free laundry products emitted any terpene at all.
Moderate evidence.
Caveats
This paper restates chemical-panel data from Steinemann 2015 and Nematollahi 2018/2019, which are not yet independently checked in this evidence base; treat the 100%-vs-0% split as a secondary report until those primaries are read directly.
Source: Goodman, Nematollahi & Steinemann 2020/2021, Air Quality, Atmosphere & Health Link to this fact
Indoor air / Test-chamber measurement
A 21-chemical VOC mixture modeled on indoor air caused dose-related increases in respiratory, eye, and other symptoms in 15 healthy adults, worsening as the chamber concentration rose from 25 to 50 mg/m3 over 4-hour exposures.
Moderate evidence: Both tested concentrations (25 and 50 mg/m3) are roughly 100-1,000x higher than typical home indoor-air VOC levels, so this does not show ordinary indoor air causes these symptoms.
Source: Pappas et al. 2000, Int J Occup Environ Health 6:1-8 Link to this fact
Indoor air / Test-chamber measurement
Removing just the two fragrance terpenes (d-limonene and alpha-pinene) from the 23-chemical mixture, while keeping ozone and the other 21 chemicals, collapsed the secondary particle pollution to background levels (2-7 micrograms per cubic meter) and eliminated most of the irritant aldehydes — identifying these two terpenes as the drivers of essentially all the ozone-initiated chemistry in this mixture.
Moderate evidence.
Caveats
Single chamber study; the 21 non-terpene VOC in the mixture are mostly saturated compounds that react very slowly with ozone, so this result may not generalize to mixtures containing other reactive unsaturated compounds.
Source: Fan et al. 2003, Environmental Science & Technology Link to this fact
Indoor air / Test-chamber measurement
A meaningful share of the formaldehyde (56-70%) and fine-particle mass (19-29%) generated when ozone reacts with fragrance terpenes comes from hydroxyl radicals that the ozone-terpene reaction itself produces as a byproduct, not from ozone reacting directly with the terpene or other chemicals.
Moderate evidence.
Caveats
The hydroxyl radical concentration itself was not measured directly but estimated from a mass-balance model using rate constants published in other studies; one of the model's own predictions (formaldehyde in the terpene-free mixture) did not match the measured value and the paper says the reason is unclear.
Source: Fan et al. 2003, Environmental Science & Technology Link to this fact
Indoor air / Self-reported survey
In a small (n=69) follow-up of Atlanta-area adults with chemical hypersensitivity, the products most commonly reported to trigger symptoms were cleaning agents (88.4%), pesticides (81.2%) and perfume (81.2%), followed by tobacco smoke (82.6%) and car exhaust (72.5%).
Moderate evidence: Small, non-random follow-up sample (n=69, about 35% of the original 199 hypersensitive respondents); self-report of trigger identification, not exposure measurement.
Source: Caress & Steinemann 2003 (EHP), Environmental Health Perspectives Link to this fact
Indoor air / Self-reported survey
The 11 household chemical products in this UK cohort's prenatal composite exposure score were used, in descending order of prevalence, as follows: disinfectant (87%), bleach (85%), aerosols (72%), air fresheners (68%), window cleaner (61%), carpet cleaner (36%), paint or varnish (33%), turpentine/white spirit (23%), pesticides/insect killers (21%), paint stripper (6%) and dry-cleaning fluid (5%).
Moderate evidence.
Caveats
Descriptive prevalence data, not an effect estimate. The 11 products were selected from an initial list of 15 by keeping only those used by at least 5% of the study sample, so rarer products are excluded from the score.
Indoor air / Review of other studies
Regulatory limits for airborne irritants like formaldehyde and ammonia are typically derived from a mouse reflex-breathing test (the Alarie/RD50 bioassay): the human occupational limit is estimated as about 3% of the mouse concentration that cuts breathing rate in half, a relationship checked across 89 chemical data pairs spanning six orders of magnitude.
Moderate evidence.
Caveats
This is a narrative review restating a decades-old correlation (Alarie 1981; Schaper 1993), not new data; the California EPA's independent check (Kuwabara 2007) adds some replication, but the underlying data pairs are not systematically re-verified here.
Source: Nielsen & Wolkoff 2017, Regulatory Toxicology and Pharmacology Industry-funded Link to this fact
Indoor air / Other evidence
For rodent inhalation studies of irritating chemicals, extending a subchronic study to predict chronic effects needs roughly a 2-fold safety margin, and extending a shorter subacute study to chronic needs about 4-fold, both smaller than the values regulators previously used (2-fold and 6-fold).
Moderate evidence: Single reanalysis by one research team of one database; not independently replicated.
Source: Mangelsdorf et al. 2021, Int J Hyg Environ Health, International Journal of Hygiene and Environmental Health Link to this fact
Indoor air / Other evidence
German government toxicologists reviewing the data behind indoor air guide values concluded there is not enough evidence to lower the standard safety margin (10 to 20 times) currently used to protect sensitive groups such as people with chemical intolerance from irritating chemicals.
Moderate evidence: This is a decision to keep an existing regulatory default under uncertainty, not new evidence that the value of 10-20 is itself correct.
Source: Mangelsdorf et al. 2021, Int J Hyg Environ Health, International Journal of Hygiene and Environmental Health Link to this fact
Indoor air / Measured in people or real products
In a sealed-room test, a reed diffuser's top three released chemicals were linalool acetate, linalool, and alpha-pinene, with linalool acetate alone making up 31-44% of everything measured.
Moderate evidence: Single product tested; sealed airtight chamber built to reach a maximum equilibrium, not a lived-in room.
Source: Zhang 2024, Cell Reports Physical Science Link to this fact
Indoor air / Measured in people or real products
Incense smoke was far more chemically complex than candle smoke: over 100 distinct VOCs, including classic wood-smoke markers (acetonitrile, methoxyphenols) and a set of nitrogen-ring compounds (pyrroles) that were completely absent from either candle's emissions.
Moderate evidence: One incense brand vs. one scented and one unscented candle product.
Source: Deng 2026, Environment International Link to this fact
Indoor air / Other evidence
In a small case series, removing mothballs and reducing scented cleaning/personal-care products, candles, and stored chemicals cut targeted indoor-air VOC categories by roughly a quarter to over 95% (e.g., naphthalene from mothballs down 96%, p-dichlorobenzene from moth crystals down 56-80%, odorants/fragrances down 26-80%) across three homes, measured by GC/MS air sampling before and after a structured home intervention.
Moderate evidence.
Caveats
Small, uncontrolled, non-blinded case series with multiple co-occurring intervention elements per home (product substitution, education, counseling, and in one case new chemical storage); cannot isolate the VOC-reduction effect from other changes.
Source: Rincón et al. 2024, Primary Health Care Research & Development Link to this fact
Indoor air / Measured in people or real products
In a 1989 NASA/ALCA interim study, sealed small chambers (0.69-0.87 m3) each holding one potted plant received a single one-time dose of benzene, trichloroethylene, or formaldehyde; over the next 24 hours, removal of that single chemical ranged from about 0% up to about 70%, depending on plant species and chemical.
Moderate evidence: Sealed chamber, zero air exchange, single pulse dose of one chemical, 24h, one plant per chamber; not a real room and the report does not claim it is.
Source: Wolverton 1989 Link to this fact
Indoor air / Government agency
The US EPA states there is currently no evidence that a reasonable number of houseplants remove significant quantities of pollutants in homes and offices, even though houseplants have been shown to reduce levels of some chemicals in laboratory experiments.
Moderate evidence: A denial of the real-room extrapolation, not a measurement; EPA cites no specific study for either the lab result or the real-room gap.
Source: US EPA, "The Inside Story" (accessed 2026-09-28) Link to this fact
Indoor air / Animal study
Not every irritating mixture became more irritating with repetition: a different fabric-softener brand (A) and a solid air freshener produced strong sensory irritation at every exposure but showed no increasing trend over three to six repeat exposures, and GC/MS analysis found almost no chemical overlap between the mixtures that did and did not show the escalating effect.
Moderate evidence: The paper could not identify which chemical(s) drive the sensitizing effect; mouse data only, single unreplicated lab.
Source: Anderson & Anderson 1999, Toxicology and Industrial Health Link to this fact
Indoor air / Measured in people or real products
Not noticing a chemical or fragrance smell in your home or workplace anymore does not mean it is gone: electro-olfactogram recordings show peripheral smell receptors stay measurably responsive to a steady background odor even after conscious perception of it has faded, because habituation happens mainly in the brain, not the nose.
Moderate evidence.
Caveats
Evidence is from small human electrophysiology studies of perception, not from measurements of continued chemical absorption, dose, or health effect; this paper does not address whether continued unnoticed exposure is harmful.
Source: Pellegrino 2017, Physiology & Behavior Industry-funded Link to this fact
Indoor air / Test-chamber measurement
Unscented reference candles emitted far less formaldehyde, benzene, and fragrance chemicals than otherwise-similar scented candles from the same study, across both small and large test chambers.
Moderate evidence: Single-lab dataset; consistent with independent findings from Salthammer 2021 and Andersen 2021 that fragrance, not wax, drives candle combustion byproduct emissions.
Source: Petry 2014, Regulatory Toxicology and Pharmacology Industry-funded Link to this fact
Indoor air / Other evidence
The particulate matter released during cleaning in this study looked like direct, mechanical spray-bottle emission rather than new particles forming from chemical reactions in the air, consistent across all four very different cleaning chemistries tested.
Moderate evidence.
Caveats
No ozone was deliberately added or measured in these experiments, and none of the four products was a terpene-rich scented cleaner, so this does not rule out secondary particle formation under different (ozone-rich, terpene-rich) conditions documented elsewhere.
Source: Souza 2025, ACS Earth Space Chem, ACS Earth and Space Chemistry Link to this fact
Indoor air / Other evidence
For 7 of 8 chemicals tracked in feminine hygiene products, a validated toxicokinetic model found that breathing ordinary indoor air contributed more to total monthly body burden than the feminine hygiene products themselves; the one exception was p-cymene, a common fragrance chemical, where product use was the dominant source.
Moderate evidence: Based on a small Michigan indoor-air sample (n=20) and a conservative worst-case dermal model; may not generalize to other regions or housing stocks.
Source: Lin 2025, Environmental Health Perspectives Link to this fact
Indoor air / Other evidence
In a room-sized test chamber with ozone at about 126 ppb, one spray of a lime-scented liquid air freshener released scent chemicals (mostly limonene) that reacted with the ozone and added about 200 micrograms per cubic meter of fine particles, up from a starting level of 13.
Moderate evidence.
Caveats
Single unreplicated chamber run (11 m3) with a generator-set ozone level and a direct spray; particle mass is calculated from particle counts, not weighed. Replicated by other chamber groups for the same mechanism, but this exact number is one run.
Source: Sarwar 2004, Journal of the Air & Waste Management Association Link to this fact
Indoor air / Other evidence
In a mouse test, mixing the pine and citrus scent chemicals alpha-pinene or limonene with ozone made a gas that cut the animals' breathing rate by about 30% and 33%; each chemical alone, at similar levels, and the ozone alone did not.
Moderate evidence.
Caveats
Mouse study (ASTM bioassay, BALB/c, n=12 per condition) at about 50-60 ppm terpene and 4-6 ppm starting ozone, far above indoor levels; part of one lab group's work; the same group later attributed about 75% of the limonene effect to formaldehyde plus leftover limonene.
Source: Wolkoff 2000, Indoor Air Industry-funded Link to this fact
Indoor air / Other evidence
In a controlled office experiment with 30 young women, more outdoor air (3, 10, then 30 liters per second per person) made the air seem fresher on entering (about 38% then 31% then 15% dissatisfied) and reduced dry mouth and throat, difficulty thinking clearly and feeling bad, while a carpet that gave off chemicals stayed in the room.
Moderate evidence.
Caveats
One 4.6-hour exposure per condition, 30 young female students, self-reported ratings, subjects could smell the difference on entering; percentages approximate (read from Fig. 4); the improvement in air quality during the sit was not significant.
Indoor air / Other evidence
Raising office ventilation did not only dilute the chemicals: higher outdoor air also brought ozone indoors (0, 4 and 16 ppb at 3, 10 and 30 L/s per person) and the room's measured sensory pollution load rose at the highest rate, so the authors favored removing sources plus ventilating rather than ventilation alone.
Moderate evidence.
Caveats
Single chamber-like office with a constant carpet source; no ozone-VOC secondary products were detected (aldehydes below detection limits), so the trade-off is a caution, not a measured harm.
Indoor air / Other evidence
A carpet used as the constant pollution source released about 127 micrograms of volatile chemicals per square meter per hour, including toluene, acetic acid, hexanal and small amounts of the scent terpenes limonene and alpha-pinene.
Moderate evidence: One used carpet, lab emission test at 23 C; terpenes were a small part of the mixture; not a fragrance product.
Indoor air / Other evidence
When limonene reacted with ozone in the test chamber, formaldehyde and two other irritant-type chemicals (4-oxopentanal and 3-isopropenyl-6-oxoheptanal) formed within the first hour, at roughly 9-17 micrograms per cubic meter each, along with a burst of ultrafine particles (average about 830 per cm3, maximum about 2,200).
Moderate evidence: Chamber chemistry at 0.7 air changes/h and 22 C with dry air; one run per condition for the chemistry; levels the authors call the upper end of indoor air.
Source: Verstraelen 2024 (J Environ Sci Health A), Journal of Environmental Science and Health, Part A Link to this fact
Indoor air / Other evidence
A computer model of typical US homes finds indoor ozone reacts almost only with terpene scent chemicals: about 99% of its reactions with indoor VOCs, with limonene (citrus) about two-thirds and alpha-pinene (pine) about a quarter.
Moderate evidence: Model, not a measurement; VOC profile is a literature median (Logue 2011), not a home with heavy scented-product use; no validation against field data.
Source: Waring & Wells 2015, Atmospheric Environment Link to this fact
Information, not medical advice. See also: myths we won’t tell you.