Every fact on this site, with its evidence grade, its caveats, and a link to the source.
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
Once normalized per gram of wax burned, the scented candle's HONO emission rate (170.77 mg per kg of wax) was an order of magnitude higher than the unscented candles' (24.14 mg/kg) or incense sticks' (52.50 mg/kg), and higher than HONO from vehicle exhaust in a traffic tunnel (88-115 mg/kg fuel).
Moderate evidence: One scented candle product tested; emission index relies on a mass-balance model of room volume and air exchange, not direct stack sampling.
Source: Deng 2026, Environment International Link to this fact
Indoor air / Measured in people or real products
Burning six sandalwood incense sticks in a living room produced isocyanic acid up to 0.38 ppb and methyl isocyanate up to 0.12 ppb, in a range the researchers compare to smoke measured downwind of large outdoor biomass fires.
Moderate evidence: One incense brand/type tested (n=3 replicate burns); methyl isocyanate stayed below the cited 0.5 ppb acute exposure limit.
Source: Deng 2026, Environment International Link to this fact
Indoor air / Measured in people or real products
The isocyanic acid released by incense tracked its precursor hydrogen cyanide almost exactly as in open biomass burning (emission ratio 0.18, within the 0.16-0.50 range reported for wildland fires), showing incense combustion runs on the same pyrolysis chemistry as biomass burning.
Moderate evidence: One incense product; mechanism (HCN to HNCO conversion pathway) inferred from correlation, not independently confirmed.
Source: Deng 2026, Environment International 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 / Measured in people or real products
During morning stir-frying, oxygenated aldehydes (formaldehyde, acetaldehyde, acetone, butanal) surged to 19.38 ppb, 91% of the total measured aldehyde signal, and on a sunny day these aldehydes rebounded upward again shortly after the stove was turned off and the hood closed, tracking a sharp rise in sunlight-driven hydroxyl radical (OH) production rather than continuing to decline.
Moderate evidence.
Caveats
Single home, comparative (non-replicate) cooking scenarios; the authors state that physical transport of pollutants from kitchen to sampling point could not be fully separated from chemical production because human occupancy ruled out using CO2 as a transport tracer.
Source: Deng 2026, Environment International Link to this fact
Indoor air / Measured in people or real products
Frying with peanut oil (29.1% linoleic acid) produced more oxidized volatile byproducts than frying with olive oil (5.01% linoleic acid), consistent with peanut oil's greater share of double bonds available for hydroxyl-radical attack.
Moderate evidence: Single comparative cooking session per oil, not replicated; ingredients also differed between sessions.
Source: Deng 2026, Environment International Link to this fact
Indoor air / Measured in people or real products
Ammonia, a byproduct rarely discussed for indoor combustion, rose 3-9 ppb above background during candle and incense burning (to 30-38 ppb total) and 4-10 ppb above background during cooking (to 30-44 ppb total), in both cases a statistically significant increase over pre-combustion levels.
Moderate evidence: Single-home measurements; cooking-related ammonia rise could not be cleanly separated from concurrent human-occupancy ammonia emissions.
Source: Deng 2026, Environment International Link to this fact
Indoor air / Other evidence
Burning scented candles releases VOCs, SVOCs, and particulate matter, including polycyclic aromatic hydrocarbons (benzo[a]pyrene, naphthalene, anthracene, pyrene) classified as carcinogenic.
Moderate evidence.
Caveats
This is a secondhand restatement in a two-page opinion piece, not a new measurement; our own chamber primaries (Salthammer 2021, Andersen 2021) independently confirm PAH/VOC output but find it strongly formulation-dependent rather than universal to all scented candles.
Source: Singh 2023, Environmental Science & Technology 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 / Measured in people or real products
General-population indoor air generally has higher styrene concentrations than outdoor air (residential surveys in the range of roughly 0.3-1.5 micrograms per cubic meter, vs. under 1 ppb / about 4.3 micrograms per cubic meter outdoors), with off-gassing from styrene-containing household products contributing to the indoor level.
Moderate evidence: Multiple national surveys (Canada, Finland, France, Germany, USA) show a fairly consistent range, but sources of indoor styrene were not quantitatively apportioned in most studies.
Source: IARC 2019 (Vol. 121) 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
In a mouse inhalation bioassay, repeating the same 1-hour exposure to fabric-softener-B emissions three times over 24 hours (concentration held constant, ~250 ppm TVOC) roughly doubled the sensory-irritation response, from 22% of breaths at the first exposure to 52% at the second and 47% at the third, while sham (clean-air) exposures stayed under 10% throughout.
Moderate evidence.
Caveats
Single, unreplicated commercial testing laboratory (the study authors' own firm); mouse data only, no measured breathing-zone concentration comparable to household air; an independent lab (Tepper 1995) failed to reproduce this lab's mouse findings for a different product class (carpets).
Source: Anderson & Anderson 1999, Toxicology and Industrial Health Link to this fact
Indoor air / Animal study
The same repeated-exposure escalation appeared with vinyl mattress-cover emissions (Brand B: 22% to 46% to 96% of breaths showing sensory irritation over three exposures) and disposable-diaper emissions (Brand B: 20% to 32% to 84%), in mice.
Moderate evidence.
Caveats
Single-lab, unreplicated mouse data; brands A, D and F mattress covers showed smaller, less consistent increases (exact values available only from the paper's figure, not the text); no comparison to measured indoor concentrations of these products.
Source: Anderson & Anderson 1999, Toxicology and Industrial Health 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 / Animal study
Air brought from a federal office building under litigation for poor indoor air quality (carried to the lab in sealed bags) caused the same objective sensory-irritation signature in mice as the consumer-product tests, dropping their respiratory rate to about 46% of baseline before partial recovery; air from buildings people considered acceptable did not cause this effect.
Moderate evidence: Single building, single lab, one comparison air sample; the underlying human complaints were not independently verified against objective health measures in this paper.
Source: Anderson & Anderson 1999, Toxicology and Industrial Health Link to this fact
Indoor air / Measured in people or real products
Modeled deposited aerosol dose from a single one-minute use of a consumer spray varied by about four orders of magnitude across 10 tested products (roughly 0.1 to 1,335 nanograms per kg body weight), and for most products (8 of 10) about 85-88% of the deposited aerosol mass landed in the head airways (nose/throat) rather than deeper in the lungs.
Moderate evidence: Deposited dose is a modeled physical mass estimate, not a measured systemic or biological dose; single-lab study of 10 products, one 1-minute exposure event per product.
Source: Nazarenko 2014, Environmental Science: Nano Link to this fact
Indoor air / Measured in people or real products
Two silver spray products (a 'nano' and a 'regular' version) were the exception to the head-airways pattern: despite having the lowest total deposited aerosol doses of any product tested (2-4 orders of magnitude below the other 8 sprays), a much larger share of their deposited dose — about 29% and 40% respectively — reached the deep alveolar region of the lungs, versus 7-9.5% for the other 8 sprays.
Moderate evidence: Absolute alveolar doses from these two products were still very small in absolute terms because total exposure was so low; this is a proportional, not absolute, finding.
Source: Nazarenko 2014, Environmental Science: Nano 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 / Other evidence
For hairspray, deodorant, and eau de toilette sprayed at the head or upper body, about 85% of the sprayed product deposits on hair, skin, or other surfaces and only about 15% stays in the air available for inhalation, as a default in the absence of product-specific measurement.
Moderate evidence.
Caveats
The only cited direct measurement behind a comparable number is a 2012 deodorant/antiperspirant aerosol study (76.5-88.6% available for inhalation, i.e., 11.4-23.5% deposited) — a different, narrower product set than hairspray/eau de toilette.
Source: Steiling et al. 2025, Toxicology Letters Industry-funded Link to this fact
Indoor air / Other evidence
Sprayed cosmetic droplets are mostly gone from the breathing zone within minutes: about 35% clear in the first minute after spraying and about 95% clear within eight minutes, which is why the authors recommend a standard 10-minute exposure duration for modeling.
Moderate evidence: The 35%/95% clearance figures are cited from a single 2021 CIR resource document, not independently replicated here.
Source: Steiling et al. 2025, Toxicology Letters Industry-funded Link to this fact
Indoor air / Measured in people or real products
In controlled chamber testing of 12 cosmetic spray products (sunscreens, dry shampoos, hair sprays, a moisturizing and a setting spray, and perfumes) applied 20 cm from the measurement point, one sunscreen spray reached a maximum PM10 particle-number concentration of 1.03 x 10^6 particles per cubic centimeter, and another reached a maximum PM10 mass concentration of 36.17 mg per cubic meter.
Moderate evidence.
Caveats
Single lab, chamber-based, near-field (20 cm) measurement of the immediate spray plume, not a room-average or personal-exposure measurement; one unit tested per product; no replication by an independent group yet.
Source: Dai et al. 2026, ACS Environmental Au Link to this fact
Indoor air / Measured in people or real products
Propellant-based cosmetic sprays (sunscreen, dry shampoo, hair spray) emitted far more submicron particles than pump-based sprays: the two pump perfumes tested stayed below 100 particles per cubic centimeter across all size fractions, while propellant sprays ranged up to hundreds of thousands of particles per cubic centimeter.
Moderate evidence.
Caveats
12 products from unnamed brands, single lab; propellant vs. pump delivery is confounded with product type (perfumes vs. sunscreens/hair sprays), so the difference cannot be attributed to propellant use alone.
Source: Dai et al. 2026, ACS Environmental Au Link to this fact
Indoor air / Measured in people or real products
Modeling with the Multiple-Path Particle Dosimetry (MPPD) model estimated that a single use of one dry-shampoo spray could deposit up to 1.38 x 10^10 submicron particles in the respiratory tract, mostly by particle count rather than mass (total deposited mass below 50 micrograms), while sunscreen sprays delivered the highest total deposited mass, up to about 2.22 milligrams per use.
Moderate evidence.
Caveats
Deposition doses are model estimates (MPPD), not measured in a human airway; the model did not account for hygroscopic particle growth or electrostatic charge, which the authors say makes the net effect on total dose uncertain.
Source: Dai et al. 2026, ACS Environmental Au Link to this fact
Indoor air / Measured in people or real products
Among the 9 air fresheners where diethyl phthalate (DEP) was detected, NRDC's 2007 test found levels ranging from 0.78 ppm to 7,300 ppm, averaging 977 ppm among DEP-containing products.
Moderate evidence: Single lab, single sample per product, not independently replicated.
Source: NRDC 2007, Clearing the Air Link to this fact
Indoor air / Measured in people or real products
At one Taoist temple in Yi-Lan, Taiwan, both particle mass and total PAH content peaked in the submicrometer 0.1-1.0 um size fraction of temple incense-burning particles: 119.0 (SD 35.2) ug/m3 particle mass and 0.19 (SD 0.002) ug/m3 total PAHs, versus 31.0/4.8 ug/m3 particle mass and 0.07/0.02 ug/m3 PAHs for the 1.0-10 um and sub-0.1 um fractions.
Moderate evidence: Field measurement from a single temple over 13 sampling days (2010); does not generalize to other temples, incense products, or ventilation conditions.
Source: Lin 2012, Science of The Total Environment 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
Across 10 real, working New York City nail salons, total VOC levels (measured in real time with a photoionization detector) averaged almost 10 times higher (32 ppm) when indoor CO2 exceeded the ANSI/ASHRAE ventilation target of 850 ppm than when the target was met (4.1 ppm).
Moderate evidence: Small (n=10), non-random convenience sample skewed toward larger, 'upscale' Manhattan salons; TVOC is an unspeciated PID sum, not a specific chemical measurement.
Source: Pavilonis, Roelofs & Blair 2018, Journal of Occupational and Environmental Hygiene Link to this fact
Indoor air / Other evidence
Mean total VOC levels measured in 10 NYC nail salons (12 ppm, median 4.0 ppm, range 0.035-67 ppm) were, in the study authors' own assessment, many times higher than would be considered acceptable in homes or office workplaces.
Moderate evidence: The paper does not give a specific numeric residential/office comparison value in text, only a qualitative 'many times greater' statement; TVOC is unspeciated.
Source: Pavilonis, Roelofs & Blair 2018, Journal of Occupational and Environmental Hygiene Link to this fact
Indoor air / Other evidence
Nail technicians' whole-blood toluene and ethyl acetate rose significantly over a single work shift (toluene 0.16→0.36 µg/L; ethyl acetate <0.16→0.51 µg/L) and post-shift levels significantly exceeded U.S. general-population (NHANES) levels for female nonsmokers.
Moderate evidence: Single small pilot study (n=10); one small cohort does not establish generalizability across the nail-salon industry.
Indoor air / Other evidence
Better ventilation (higher air changes per hour) was significantly associated with lower personal-air toluene in nail salons (Spearman r=-0.76, p=0.017), but also with higher salon-area methyl methacrylate (r=0.71, p=0.034).
Moderate evidence.
Caveats
Small sample (7 salons); the positive ACH-methyl-methacrylate correlation is the opposite of the expected direction and is only the authors' hypothesis (increased monomer evaporation at higher airflow), not confirmed.
Indoor air / Test-chamber measurement
Standardizing 196 results from 12 published potted-plant VOC-chamber studies into clean air delivery rate (CADR), the typical (median) houseplant removes VOCs at about 0.023 m3/h, roughly 4,000 times weaker than a standard portable air cleaner (~100 m3/h).
Moderate evidence.
Caveats
Best-case estimate; the underlying mass-balance models assumed negligible chamber leakage and surface sorption, both of which would inflate apparent plant removal, so true removal is likely smaller still.
Source: Cummings & Waring 2020, Journal of Exposure Science & Environmental Epidemiology Link to this fact
Indoor air / Other evidence
To match the VOC removal that ordinary outdoor-to-indoor air exchange already provides in a typical home or office (~1 h-1 air exchange rate), a room would need 10 to 1,000 potted plants per square meter of floor space.
Moderate evidence: Best-case plant-performance assumption (no chamber leakage/sorption); ceiling height held constant at 2.5 m across the analysis.
Source: Cummings & Waring 2020, Journal of Exposure Science & Environmental Epidemiology Link to this fact
Indoor air / Other evidence
Even using the best-performing plants (90th percentile of the dataset) in an unusually airtight building, one potted plant per square meter of floor area (already impractically dense for interior design) achieves only about 20% of the VOC removal that air exchange alone provides.
Moderate evidence: Requires both an unusually low air exchange rate (<0.2 h-1) and the single best-case CADRp tier; falls off quickly at more typical air exchange rates.
Source: Cummings & Waring 2020, Journal of Exposure Science & Environmental Epidemiology Link to this fact
Indoor air / Other evidence
A historical calculation (Levin 1992), using the most generous reading of the early Wolverton/NASA chamber data, found a typical ~140 m2 (1,500 ft2) house would need 680 houseplants (4.9 plants/m2) just to raise plant-driven VOC removal to 0.096 h-1, about an order of magnitude below normal air exchange and called 'obviously not attainable.'
Moderate evidence: Uses the most generous (best-case) early NASA dataset; independently replicated in direction and order of magnitude by this paper's own larger analysis.
Source: Cummings & Waring 2020, citing Levin 1992, Journal of Exposure Science & Environmental Epidemiology Link to this fact
Indoor air / Measured in people or real products
In a field study of two Michigan hotels, hotel housekeepers' and other staff's personal breathing-zone VOC exposure while working (57 ± 36 µg/m3 total target VOCs) was nearly twice the level measured by stationary indoor-area monitors in the same hotels (28 ± 15 µg/m3), and both were far above outdoor levels (mostly below detection).
Moderate evidence: Small sample (2 hotels, 22-23 personal samples); short 6-9 hour sampling shifts; not generalizable to other hotels.
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 this hotel study, airborne formaldehyde — the single biggest driver of estimated health risk — did not track terpene-fragrance levels or season (terpene-ozone secondary chemistry would be expected to rise with summer ozone), leading the authors to attribute it instead to building materials, furnishings, and the large volume of bedding and towels used in hotels, not to the terpene-containing cleaning and laundry products.
Moderate evidence: Attribution is inferential, not source-tested directly; the authors call for further study to verify formaldehyde sources in hotels.
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
Ordinary spray-and-wipe cleaning with quats, bleach, hydrogen peroxide, or a thymol-based botanical disinfectant raised indoor fine-particle (PM2.5) levels by 0.7-14.5 micrograms per cubic meter and total-VOC sensor readings by 10-104 ppbv, measured across a residential bathroom, a university office, two chemistry labs, and a hotel in Canada.
Moderate evidence: Single study, small replicate counts per cleaner/location, and the TVOC sensor is explicitly non-quantitative.
Source: Souza 2025, ACS Earth Space Chem, ACS Earth and Space Chemistry Link to this fact
Indoor air / Other evidence
The lowest-ventilation room tested, a residential bathroom with an air change rate under 1 per hour, showed 146-346% higher cleaning-related PM2.5 increases and about 7-fold higher TVOC increases than a university office and lab with 5.9-9.1 air changes per hour, for the same cleaning products.
Moderate evidence: One bathroom, one office, two labs; not a dose-response series across many ACR values.
Source: Souza 2025, ACS Earth Space Chem, ACS Earth and Space Chemistry 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
Bleach cleaning produced a two-humped (bimodal) rise in total VOC readings, a pattern consistent with bleach's chlorine-based oxidants reacting with ordinary indoor VOCs to form new, oxidized compounds, rather than only releasing VOCs directly.
Moderate evidence: The oxidized compounds were not chemically identified in this study; the PID gives only a total, non-specific VOC signal, so this is an inferred mechanism, not a confirmed one.
Source: Souza 2025, ACS Earth Space Chem, ACS Earth and Space Chemistry Link to this fact
Indoor air / Other evidence
During real COVID-19 disinfection at a hotel, repeated use of a quats-based disinfectant raised fine-particle levels by 5.5 to 14.2 micrograms per cubic meter in the lobby, elevator, and a public bathroom, exposing cleaning staff to repeated particle bumps throughout a work shift.
Moderate evidence.
Caveats
One day of field measurement, one hotel; cleaning protocol there also deviated from the product label (solution left on surfaces rather than wiped off) to reduce staff vapor exposure.
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
The industry / Self-reported survey
Even the companies selling products often don't know everything in them: all 20 'leader' consumer-product companies interviewed said ingredient or hazard information could be hard to get from suppliers, and 7 named suppliers' trade-secret claims as a major obstacle.
Moderate evidence: Interview study, 20 self-selected companies, 2009; no fragrance firms identified.
Source: Scruggs 2011, Environmental Science & Policy Link to this fact
The industry / Self-reported survey
Only 1 of 20 leading consumer-product companies could test its own products' chemistry in-house; most relied on suppliers' signed promises (18 of 20).
Moderate evidence: Counts are interview mentions.
Source: Scruggs 2011, Environmental Science & Policy Link to this fact
The industry / Lab study (cells or chemistry)
The fragrance industry's own data show its main explanation for how fragrance chemicals cause allergy doesn't cover most of them: 34 of 62 ingredients (55%) sensitize despite having no predicted protein-binding alert.
Moderate evidence.
Caveats
Structural-alert software limitation; metabolic activation explains some. Roberts & Api 2018 (different 57-chemical fragrance dataset, no direct overlap confirmed with this claim's 62-chemical set) adds two further indirect-activation routes the alert software here evidently does not capture — slow autoxidation of tertiary allylic/benzylic C-H compounds to allergenic hydroperoxides/epoxides, and a proposed bio-sulfation route for benzylic alcohols — which could explain part of the unexplained 55% for chemicals with those structural motifs. The same paper separately proposes that some LLNA-positive, alert-free fragrance chemicals (hexyl/benzyl salicylate) may be LLNA false positives rather than true sensitizers at all, which would pull in the opposite direction (shrinking, not explaining, the true no-mechanism fraction) if any such chemicals are present in this claim's 62-ingredient set — not checked here, so the net effect on the 55% figure is unresolved and the grade is left unchanged.
Source: Lee 2024, Food and Chemical Toxicology Industry-funded Link to this fact
The industry / Lab study (cells or chemistry)
The non-animal tests now used to set fragrance safety levels are typically off by about 2 to 3 times when predicting how potent an ingredient is.
Moderate evidence.
Caveats
Median absolute fold-misprediction 1.8-3.4; errors tend to be conservative. Natsch 2023 (same regression framework, non-fragrance-specific dataset) finds the underlying models are robust to retraining against human rather than LLNA data (only 6/139 chemicals shift >3.3-fold) — weak indirect support that this fold-error range is a stable property of the method, not an LLNA-fitting artifact, though the 62-fragrance-ingredient set itself is not retested against human data.
Source: Lee 2024, Food and Chemical Toxicology Industry-funded Link to this fact
The industry / Lab study (cells or chemistry)
Those models underestimated allergy potency by more than fivefold for 18% of the 188 chemicals tested, and more than tenfold for 11%.
Moderate evidence.
Caveats
Prediction error, not a safety-limit error; worst outliers are non-fragrance chemicals. Natsch 2023 (same author, human-anchored retraining) shows this outlier structure is not simply an artifact of fitting to mouse data: only 6/139 chemicals (4.3%) shift by more than 3.3-fold when the same models are retrained against human-anchored potency values instead of LLNA.
Source: Natsch & Gerberick 2022, ALTEX Industry-funded Link to this fact
The industry / Animal study
Older synthetic musks (musk ambrette, AETT) caused nerve damage in animal studies and were later restricted.
Moderate evidence.
Caveats
Both primaries now read directly (2026-09-26): Spencer 1979 (AETT, N=16, single lab, single route) and Spencer 1984 (musk ambrette, N=220, dual route, dose-ranging). The musk-ambrette evidence alone is large and well-controlled enough to support 'strong', but the claim bundles it with the smaller AETT study, which keeps the combined claim at moderate under the grading rule.
Source: Pinkas 2017, Environmental Research Link to this fact
The industry / Journalism
A perfumer writing in a chemistry journal said a natural ingredient such as rose oil is sometimes added in a "negligible quantity only to be able to say that you have rose oil in your formula", which "will please the marketing people" but does nothing for the scent.
Moderate evidence: Opinion; she advises against the practice and gives no frequency.
Source: Ellena 2008, Chemistry & Biodiversity Industry-funded Link to this fact
The industry / Animal study
Citronellol is treated as safe by default – GRAS at the US FDA, a 'non-toxic' biopesticide at the US EPA, and limited only by the fragrance industry's own voluntary IFRA standard – yet this government-funded study found it is brain-penetrant and calls for its content in consumer products to be regulated.
Moderate evidence: The call for regulation is the authors' conclusion from high-dose animal data; funded by the Korean Ministry of Environment, no industry money.
Source: Kim 2024, Journal of Hazardous Materials Link to this fact
The industry / Review of other studies
The industry's permitted levels for rose ketones (up to 0.07-0.8% depending on product type) overlap the concentrations at which already-sensitized volunteers reacted (0.05-0.1%), because the risk assessment is designed to prevent new allergies rather than to protect people who already have one.
Moderate evidence.
Caveats
The loosest categories are rinse-off/incidental contact where dose per area is far lower than a patch test. The design intent (induction only, not elicitation) is now confirmed by the framework's own current methodology paper (Api 2020, QRA2 §2.2); the numeric overlap still rests on the single 2007 dossier.
Source: Lalko 2007 (RIFM), Food and Chemical Toxicology Industry-funded Link to this fact
The industry / Review of other studies
The fragrance industry's safety assessment of 17 salicylates counted exposure from 10 personal-care product types only. Household cleaners and detergents, which the same report lists as uses, and breathing fragrance in were not included.
Moderate evidence.
Caveats
As of 2024, RIFM/Creme Global's aggregate exposure model (Lee 2024) does now cover household care, air care, and inhalation industry-wide, but that 2024 paper does not report salicylate-specific numbers, so it is unconfirmed whether this specific 2007 dossier's gap has since been closed for these 17 materials. A decade after this 2007 dossier, RIFM's own broader exposure model (Comiskey et al. 2017, Phase 2) had still not reached household cleaning or laundry products either — explicitly named as future work — confirming the product-type gap this claim describes persisted within the industry's own more advanced modeling program well past 2007, closing only with Lee 2024 industry-wide (still not salicylate-specific).
Source: RIFM Expert Panel / Belsito 2007, Food and Chemical Toxicology Industry-funded Link to this fact
The industry / Review of other studies
The industry panel judged each salicylate's safety one chemical at a time, although the same report says all 17 are broken down in the body to the same substance, salicylic acid.
Moderate evidence.
Caveats
The combined-exposure figure (about 1.05 mg/kg/day, group margin roughly 48-69 at the panel's own 100%-absorption default) is a evidence base calculation on the paper's Table 1, not a published number, and sums high-end maxima.
Source: RIFM Expert Panel / Belsito 2007, Food and Chemical Toxicology Industry-funded Link to this fact
The industry / Measured in people or real products
In a French fragrance-and-flavor factory, the company's own measurements found the butter-flavor chemical diacetyl (linked to 'popcorn lung' in US factory workers) in workers' breathing air at 0.05–9 ppm during short tasks; 29 of 31 samples were above the 15-minute limit of 0.1 ppm recommended by the EU's scientific committee on occupational limits.
Moderate evidence.
Caveats
Limit comparison is our (paper makes none); samplers on clothing, respirator use per task not reported; flavor chemical, factory workers, not consumers; industry-funded (V. Mane Fils).
Source: Angelini 2016, PLoS ONE Industry-funded Link to this fact
The industry / Measured in people or real products
The standard EU (REACH) screening tool for estimating workers' chemical exposure predicted lower levels than were actually measured in 61% of 431 measurements in a fragrance-and-flavor factory, sometimes by more than 100-fold.
Moderate evidence: One plant; evidence base count from the paper's S4 table (paper: 37% of tool predictions were above the measurement); short task samples.
Source: Angelini 2016, PLoS ONE Industry-funded Link to this fact
The industry / Self-reported survey
More than a third of Germans (37.8%) think people who wear perfume are more hygiene-conscious; fragrance can mask a smell but does not clean.
Moderate evidence: Attitude item; the 'does not clean' half is the author's argument, not a measurement.
Source: Klaschka 2020, Environmental Sciences Europe Link to this fact
Information, not medical advice. See also: myths we won’t tell you.