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
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
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
A limonene-scented foam cleaner released formaldehyde, an irritant and carcinogen, both directly and through reactions with ozone after use.
Moderate evidence.
Caveats
Primary formaldehyde source ingredient unidentified (Rossignol's own ISO chamber measured 25.6 ug/m2/h at 0-30 min without ozone). Destaillats 2006 tested three different terpene-containing products (pine-oil cleaner, orange-oil degreaser, plug-in air freshener) under controlled bench conditions and found NO primary formaldehyde in any of them (negligible before ozone was added). This does not contradict Rossignol's own direct measurement of a different, specific product, but it shows primary formaldehyde is not a general feature of terpene/fragrance cleaners, supporting the reading that Rossignol's primary source is a formulation additive (e.g. a preservative or surfactant impurity) rather than the fragrance/terpene component itself.
Source: Rossignol 2013, Atmospheric Environment Link to this fact
Indoor air / Measured in people or real products
Scent was only part of what a scented cleaner released: its glycol-ether solvent reached about 1,100 ug/m3 in room air against 71 ug/m3 for limonene.
Moderate evidence.
Caveats
One product; Singer 2006 (Indoor Air, 5 more US cleaners, 50 m3 room) found the opposite pattern in a cleaner containing both a glycol ether and limonene (limonene 3-5x the 2-BE), so 'solvent exceeds scent' is product-specific, not general.
Source: Rossignol 2013, Atmospheric Environment Link to this fact
Indoor air / Review of other studies
EU researchers attributed large swings in home limonene levels within the same city to whether people had used a fragrance, air freshener, or cleaning product before the air was sampled.
Moderate evidence.
Caveats
Authors' interpretation of variance; a larger, more rigorous 60-home UK diary study (Heeley-Hill 2021) found cumulative product-use frequency has little predictive power for measured concentrations (R²<0.001), with only weak covariance between limonene and insecticide/plug-in-air-freshener use specifically, not general fragrance/cleaning-product use Note the exposure measures differ: this claim concerns product use shortly before sampling, whereas Heeley-Hill 2021 tested cumulative use frequency over the sampling period, so it does not directly test the claim. Evidence is mixed: Wang 2017 (25 UK homes) found the highest-limonene homes were heavy product users; Heeley-Hill 2021 (60 UK homes; fieldwork funded by Givaudan, a fragrance manufacturer; analysis by the University of York) found frequency predicted little.
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
Pure limonene only irritates human eyes at about 445 mg/m³, far above indoor levels. A limonene-ozone mixture reacted for just 10 minutes raises eye-blink rates at roughly 1,000-2,000x less limonene: Klenø & Wolkoff (2004, n=8, primary) found residual 0.42 mg/m³ limonene + 0.08 mg/m³ ozone raised blink frequency 42% (P<0.0001); Nøjgaard (2005, n=10, primary) found a lower dose, 0.23 mg/m³ limonene + 0.08 mg/m³ ozone, gave a smaller but still significant +17% (p=0.003).
Moderate evidence.
Caveats
Fadeyi et al. 2015 (now read directly; n=71 — 38 non-asthmatic, 33 mild asthmatic, corrects an earlier undifferentiated count — 3 h, whole-body) found no significant eye/nose/throat irritation difference between asthma-status groups, at doses comparable-to-LOWER than Kleno/Nojgaard's residual concentrations, not higher as previously stated: limonene 35-36 ppb vs. Kleno's 75 ppb / Nojgaard's 41 ppb, and ozone 20-37 ppb (rising) vs. their steady ~41 ppb. This is a different endpoint (self-reported symptom rating vs. objective blink count), and the study has no unexposed/clean-air control arm, so 'no significant' is a between-group comparison with ratings staying below the scale's 'slight irritation' anchor, not a formal null against no exposure. Not a refutation of the blink-frequency result, but it tempers real-world relevance at doses at or below the LOEL pair, over a much longer (3 h vs 20 min), whole-body exposure. Laumbach et al. 2005 (n=130, same chamber cohort as Fiedler 2005) adds a whole-body objective-biomarker null at a higher combined terpene dose (limonene 125 ppb + alpha-pinene 160 ppb, with ozone, 135 min): no nasal symptom or nasal-lavage PMN/IL-6/IL-8/protein change. It's a different route and endpoint from the single-eye blink studies, so it doesn't refute them, but it weighs against generalizing them.
Source: Wolkoff 2013, International Journal of Hygiene and Environmental Health Link to this fact
Indoor air / Other evidence
In mouse tests, about three-fourths of the airway irritation from limonene reacting with ozone came from formaldehyde and residual limonene together (formaldehyde the dominant contributor, at roughly 17-22 percentage points; residual limonene a small but real contributor, under 5 percentage points), not from the particles.
Moderate evidence.
Caveats
Animal data at ppm-range reactants; the author's own lab; not independently replicated by another group. This is now grounded directly in the true primary, Wolkoff et al. 2008 (*Toxicol Lett* 181:171-176), read in full: its own Abstract and Conclusion state formaldehyde and residual limonene COMBINED explain 'up to three-fourth' (~75%), correcting this page's earlier paraphrase ('two-thirds, formaldehyde only, excluding limonene') which had both the wrong number and the wrong attribution. The entire conducting-airway (VD/VT, airflow-limitation) effect's causal chemical remains unidentified in the primary.
Source: Wolkoff 2013, International Journal of Hygiene and Environmental Health Link to this fact
Indoor air / Review of other studies
An indoor-air toxicologist recommends measuring limonene in offices because this common fragrance 'easily undergoes ozonolysis producing oxidation products that includes formaldehyde'.
Moderate evidence.
Caveats
Wolkoff & Nielsen 2017 (same author) reinforces the same recommendation-level framing and adds a quantitative synthesis ('>200 ug/m3 ozone at high limonene concentrations would be necessary to expect sensory airway and eye effects'), consistent with human nulls in Fiedler 2005 and Fadeyi 2015. Laumbach et al. 2005 (n=130, now read directly, the Fiedler cohort's nasal-lavage companion) adds a null on the one endpoint most directly relevant to a monitoring recommendation for a chemical that 'easily undergoes ozonolysis': no nasal symptom or objective nasal-inflammation-marker change despite the same ozonolysis chemistry occurring (formaldehyde and SOA both confirmed to rise during exposure). This keeps the claim at the level of a monitoring/indicator recommendation, not a finding of harm at current office levels.
Source: Wolkoff 2013, International Journal of Hygiene and Environmental Health Link to this fact
Indoor air / Measured in people or real products
A new Little Tree car air freshener releases most of its limonene in the first few days: in a closed car the limonene signal halved roughly every day and was nearly gone within 4-5 days.
Moderate evidence: Relative peak areas only, no concentrations; one car and one scent; baseline not shown.
Source: Pino-Delgado 2021 (J Student Res), Journal of Student Research 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 / 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 / Test-chamber measurement
A car air freshener's own terpenes (alpha-pinene, beta-pinene, p-cymene, limonene) react with in-vehicle ozone to form ultrafine particles and irritant gases (formaldehyde, acetaldehyde, acrolein) that never appear on the product's ingredient list, because they are made in the cabin air, not sold in the bottle.
Moderate evidence.
Caveats
N=1 product (oil-based liquid, citrus); single run per condition, no replicates; the 100 ppb ozone condition exceeds the paper's own cited in-vehicle ozone range (2-86 ppb) and RH/ventilation were excluded, so treat the numbers as chemistry demonstration, not a real-commute dose.
Source: Lamorena & Lee 2008 (J Hazard Mater), Journal of Hazardous Materials Link to this fact
Indoor air / Measured in people or real products
In a real working primary school, mopping a classroom with a limonene-containing detergent produced bursts of tens of thousands of tiny new particles per cubic centimeter within minutes, but only when ozone was present in the air; a plain water-only mop produced no such burst.
Moderate evidence.
Caveats
One school, one detergent; particle number not mass. Classroom mopping peak ~35,000/cm3; matched controlled lecture-theater trials with the same detergent confirmed peaks up to ~68,500/cm3.
Source: Morawska 2009, Environmental Science & Technology Link to this fact
Indoor air / Measured in people or real products
A limonene-cleaning event needs indoor ozone above roughly 5 parts per billion to trigger a detectable burst of new ultrafine particles; below that threshold, in this study's controlled trials, essentially no particle formation occurred.
Moderate evidence.
Caveats
One product, one 140 m3 lecture theater, one air-exchange rate (1.08/h); threshold is specific to this detergent's limonene loading and may not generalize to other products or rooms.
Source: Morawska 2009, Environmental Science & Technology Link to this fact
Indoor air / Measured in people or real products
A 10-minute-old reacted mixture of limonene and ozone (residual 75 ppb limonene + 40 ppb ozone) raised human eye-blink frequency 42% relative to clean air, while the same men's eyes exposed separately to just limonene, or just ozone, at similar or higher levels, did not blink more.
Moderate evidence.
Caveats
Small (n=8), single-lab, local single-eye exposure (not whole-body). Starting limonene (220 ppb) and residual limonene (75 ppb) are one to two orders of magnitude above typical indoor levels (usually <10 ppb, up to ~70 ppb in cleaning agents/new housing, per the authors' own Introduction). A same-lab follow-up re-test of a nominally comparable mixture gave a 3.5x smaller effect (12% vs 42%), so the magnitude has not replicated within the same group.
Indoor air / Review of other studies
The four most common airborne fragrances in homes and offices, pinene, limonene, linalool, and eugenol, are usually present at levels 2 to 3 times below the concentration needed to physically irritate the eyes and airways, but at or above the much lower level needed just to smell them.
Moderate evidence.
Caveats
Sensory-irritation thresholds here are derived (mouse RD50 values run through a regression, or human LOAELs divided by an assessment factor of 5), not all directly measured; this restates the same author group's own 2013 conclusion for an updated audience, not independent confirmation.
Source: Wolkoff & Nielsen 2017, Environment International 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
The UK home with the heaviest, most frequent use of cleaning and fragranced products (9 different products, some used more than 10 times in a week, plus a scented candle) had a 5-day average D-limonene concentration of up to 1,439 ug/m3, around 80 times the study's median home and possibly the highest domestic value reported in the literature at the time.
Moderate evidence: Single home out of 25 driving the extreme; 5-day average, not a short-term peak, which the authors state was likely higher.
Source: Wang 2017, Environmental Science: Processes & Impacts Link to this fact
Indoor air / Measured in people or real products
Even with daily diary records of exactly how often 60 households used 13 different types of scented and cleaning products over three days, how often people used these products did not predict how much VOC was in their home's air (R-squared less than 0.001 for total VOC; no individual VOC, including limonene, showed a significant relationship).
Moderate evidence: Frequency of use, not dose per use or product formulation, was recorded; a narrow, weak exception existed for limonene with insecticide/plug-in-air-freshener use specifically.
Source: Heeley-Hill 2021, Environmental Science: Processes & Impacts Industry-funded Link to this fact
Indoor air / Animal study
In a mouse study, when scientists physically separated the invisible ultrafine particles from the gas fumes made by citrus-scent limonene reacting with ozone, the airway-irritating effect disappeared entirely, showing it's the gas products, led by formaldehyde, that irritate, not the particles themselves.
Moderate evidence.
Caveats
Single lab, not independently replicated. Mouse ppm-range reactant concentrations are several orders of magnitude above real indoor limonene/ozone levels; this is a causation/mechanism study, not an exposure-response study at realistic doses.
Source: Wolkoff et al. 2008, Toxicology Letters Link to this fact
Indoor air / Animal study
In the same mouse study, formaldehyde formed by the limonene-ozone reaction, together with the leftover limonene itself, accounted for roughly three-quarters of the airway-irritating effect measured; formaldehyde was the dominant contributor.
Moderate evidence.
Caveats
Single lab, single animal study; the estimate for formaldehyde and limonene's individual contributions is model-based (from the group's own earlier single-compound dose-response studies), not a direct blocking experiment. The remaining ~25% of the effect, and the entire conducting-airway (airflow-limitation) effect's causal chemical, are unidentified.
Source: Wolkoff et al. 2008, Toxicology Letters 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
Switching to fragrance-free laundry detergent also reduced D-limonene in the laundry room's own indoor air, not just at the dryer vent, by up to 72.7% (mean 45.8%) within one month.
Moderate evidence: 4 households, single background-air sample per round, no statistical testing.
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
In a chamber test at a realistic indoor ozone level (~40 ppb), adding ozone to an indoor-representative mixture containing the fragrance terpenes d-limonene and alpha-pinene generated formaldehyde (13 to 40 micrograms per cubic meter), several other irritant aldehydes, organic acids, and fine secondary particle pollution (140 micrograms per cubic meter, versus under 5 without ozone).
Moderate evidence.
Caveats
Single chamber study, one research group; the total VOC and terpene concentrations used (6.6 ppm total VOC, 125-160 ppb terpenes) were deliberately set above typical nonindustrial indoor air, by the authors' own statement, to match a specific human-exposure protocol.
Source: Fan et al. 2003, Environmental Science & Technology 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 / Measured in people or real products
Hotel housekeepers' real occupational personal exposure to fragrance terpenes (mainly limonene and alpha-pinene) from direct, repeated contact with cleaning and laundry products averaged just 7.7 µg/m3, even though every cleaning product tested in the study contained terpenes (up to 64 µg/mL in one smoke-removal spray).
Moderate evidence: Occupational, not general-population exposure; short sampling window (6-9h); small sample.
Indoor air / Measured in people or real products
In a 2021 pilot study of 20 real nail salons in the NYC area, toluene (median 7.03 ppb) and d-limonene (median 4.21 ppb) were the two most abundant of 31 volatile organic compounds measured in the air, and the authors attribute the d-limonene to cleaning and disinfection products rather than nail products, since d-limonene is not a nail-product ingredient.
Moderate evidence.
Caveats
Small convenience sample (n=20), area/micro-environmental air sampling only (not personal exposure), sampled during COVID-19 when cleaning frequency was likely elevated; source attribution to cleaning products is the authors' inference, not measured (no product-ingredient data collected).
Source: Han et al. 2022 Link to this fact
Indoor air / Measured in people or real products
Nail salons serving 30 or more customers per day had significantly higher air d-limonene (median 6.18 ppb) than salons serving fewer than 30 customers (median 2.30 ppb, p=0.044), consistent with more frequent cleaning of tables between customers.
Moderate evidence: Single small pilot study; cleaning-product use itself was not directly measured or recorded, only inferred from customer volume and observed cleaning behavior.
Source: Han et al. 2022 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 / Measured in people or real products
In those spa salons, terpenes made up about 22% to 86% of the airborne VOC total on the days charted, and limonene was the most abundant terpene in all four.
Moderate evidence: Range from one example day per salon (Fig. 3), not all 60 samples; non-limonene VOCs are toluene-equivalent estimates.
Source: Pytel 2021, Environmental Science and Pollution Research Link to this fact
Indoor air / Measured in people or real products
What fills a treatment room's air depends on the oils used: limonene-rich oils such as orange or grapefruit gave limonene-dominated air, while rose oil gave none.
Moderate evidence: Few days per salon, oil mixtures often unknown or blended with additives; association by day, not controlled comparison.
Source: Pytel 2021, Environmental Science and Pollution Research Link to this fact
Indoor air / Other evidence
The same car sprays raised limonene, ethyl acetate, and cyclohexane in the cabin air; limonene at the driver seat in one medium SUV rose from about 10 to about 125 micrograms per cubic meter (about 165 with another spray).
Moderate evidence.
Caveats
Single small lab study; limonene values are read from a chart, so they are approximate; the small SUV had a much higher unexplained limonene baseline (about 280 micrograms per cubic meter before spraying, read from Fig. 5b3).
Source: Lee 2024, Science of The Total Environment 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
The concentrations in this mouse test were much higher than found indoors: about 48-56 ppm of leftover terpene and 4-6 ppm of starting ozone, versus indoor limonene or pinene maxima of roughly 45-70 ppb and indoor ozone up to roughly 150 ppb (the wiki's conversions of the paper's tables).
Moderate evidence.
Caveats
Our arithmetic from the paper's printed tables; the authors justify the doses by mouse insensitivity (about 10x less sensitive than humans) and the need for over 90% ozone consumption in 30 s.
Source: Wolkoff 2000, Indoor Air Industry-funded Link to this fact
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 / Test-chamber measurement
In a 2.5 m3 test room ventilated at about 0.5-0.8 air changes per hour, pulses of 60-100 ppb ozone added to air containing limonene (the lemon scent in many air fresheners and polishes) produced new submicron particles within minutes; later pulses grew them to larger submicron sizes.
Moderate evidence: Single runs per condition, one lab, injected limonene, ozone set by a generator; particles below 0.1 um and particle chemistry were not measured; no health outcome.
Source: Wainman 2000, Environmental Health Perspectives 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
Indoor air / Other evidence
In 30 closed Korean homes with no other scented products allowed, putting three Vicks plants in the living room raised room limonene about 1.5 times for plants in soil and about 2.3 times for plants in water over 3 hours; alpha-pinene rose about 1.5 and 2.5 times.
Moderate evidence.
Caveats
One plant species, 3-hour windows, 30 homes, conditions not randomized in order (soil day then water day), small closed rooms; the alpha-pinene rise for soil plants was not significant (p = 0.057).
Information, not medical advice. See also: myths we won’t tell you.