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.
Health effects / Review of other studies
Doctors have published detailed reports of 12 young children (8 boys, 4 girls) whose breasts began to grow while they used lavender or tea tree oil products such as colognes, baby bath soap, or hair gel; in every case the growth went away within months of stopping.
Weak evidence: Case reports only; no rechallenge; this kind of breast growth often regresses on its own; the review itself concludes causation is not shown.
Source: Braunstein & Braunstein 2023, touchREVIEWS in Endocrinology Industry-funded Link to this fact
Health effects / Lab study (cells or chemistry)
In human adrenal cells, eight common fragrance terpenes — eucalyptol, geraniol, carvone, 3-carene, ocimene, both pinenes, and dihydro-beta-ionone — cut production of the androgen precursor DHEA by 13–31%, and six others cut the activity of aromatase, the enzyme that makes estrogen, by 22–33%.
Weak evidence.
Caveats
Single 10 µM concentration, ~140–200× above what indoor air or ordinary product use could produce internally; the mass-spectrometry check was non-significant for eucalyptol (p = 0.0574) and null for dihydro-beta-ionone; the same 10 µM killed up to 50% of a prostate-cancer cell line by 48 h. Always state the concentration.
Health effects / Lab study (cells or chemistry)
In a lab-grown 3D model of human skin, polystyrene fragments up to 10 µm were cytotoxic and inflammatory in keratinocytes, but only the fragments 2 µm or smaller penetrated into the dermis (average maximum 4.7 µg) within an hour, switching on inflammation genes there.
Weak evidence.
Caveats
One 3D skin model study (Song 2024); independently read the same way by a second review (Menichetti et al. 2025, J Xenobiot), which also reports the <2 µm penetrating cutoff and notes that in ex vivo human and mouse skin from the same primary study, the cutoff for any penetration was stricter still, under 1 µm. Not intact living human skin; no real-use dose.
Health effects / Lab study (cells or chemistry)
Many perfumes contain strongly antibacterial compounds: activity against Gram-negative bacteria appeared at 50 billionths of a liter, and a single spray is about 2,000 times that amount.
Weak evidence: Plate assay with a marine bacterium; effect on the skin microbiome inferred by the authors, not tested.
Source: Morlock & Heil 2025, Journal of Chromatography A Link to this fact
Health effects / Measured in people or real products
In the same test, patients rated breathlessness and cough higher after perfume at the eyes (1.5 vs 0.4 and 0.9 vs 0.3 on a 0-3 scale), yet lung function, oxygen saturation, and breathing rate did not change at all.
Weak evidence: Single-blind (scorers apparently not blinded), 3 of many symptoms analyzed, n=11; the airway symptoms did not replicate double-blind (Elberling 2006: 6/11 perfume vs 5/11 placebo).
Health effects / Lab study (cells or chemistry)
A small 2026 follow-up study found mutagenic and cell-killing compounds in 8 perfumes, consistent with an earlier 42-perfume finding from the same German lab.
Weak evidence.
Caveats
Same lab and platform as the earlier study, not independent; only 8 unnamed perfumes, unclear overlap with the 42; simulated liver metabolism was built for this paper but explicitly not tested on the perfumes; no antibacterial or hormone-related endpoints were run.
Source: Schmidtmann 2026, Analytical Chemistry Link to this fact
Health effects / Measured in people or real products
A small clinic study found that a real cologne challenge produced an objective, reproducible 18-58% drop in FEV1 (lung function) within minutes in asthma patients who already reported cologne sensitivity, blocked mostly by bronchodilators rather than cromolyn or blocking the sense of smell.
Weak evidence: N=4 evaluable patients, unblinded first exposure, cologne dose never measured, single cologne brand, all pre-selected for a cologne-sensitivity history, 1986, unreplicated.
Source: Shim & Williams 1986, The American Journal of Medicine Link to this fact
Health effects / Measured in people or real products
Pleasant fragrance smells can measurably calm the body (raising a marker of parasympathetic "rest and digest" activity by up to 47% for pine scent and 26% for citrus), but once that same citrus scent has reacted with ozone, the calming effect reverses into a small drop in that same marker.
Weak evidence.
Caveats
Each condition (pure pine, pure citrus, and the ozone-reacted citrus mixture) comes from a separate, small study, not one head-to-head design; the review's own authors suggest perceived unpleasantness of the reacted mixture, not necessarily toxicity, may explain the reversal.
Source: Wolkoff & Nielsen 2017, Environment International Link to this fact
Health effects / Self-reported survey
In a 10-year longitudinal follow-up of a German young-adult cohort (SOLAR, n=1,143), only participants who persistently used multiple disinfectants and cleaning products (sprays, disinfectant sprays, and nonspray disinfection methods) weekly at two assessments 10 years apart showed an elevated point estimate for current asthma (OR 1.68) and current wheeze (OR 1.71) compared with no weekly use; neither reached statistical significance (95% CI 0.48-5.88 and 0.75-3.90).
Weak evidence.
Caveats
Same underlying cohort as Weinmann 2017 (SOLAR 2 exposure data reused); small persistent-use subgroup (8.2% of n=1,143); wide confidence intervals; incident-asthma/wheeze estimates too imprecise for inference; authors draw no causal conclusion.
Health effects / Animal study
When the air freshener's emissions were combined with fresh latex-paint emissions, the mixture was not less toxic in mice than paint alone — the behavioral (FOB) score rose further and significantly, countering claims that air fresheners neutralize or mask other indoor pollutants.
Weak evidence: Single product, single co-pollutant, one dose combination, mouse behavioral scoring only; not tested with other pollutant classes or in humans.
Source: Anderson & Anderson 1997, Archives of Environmental Health Link to this fact
Health effects / Other evidence
California state scientists estimate that cosmetics may account for at least 4% (and plausibly much more, given wide uncertainty) of the PFOA-related chemicals measured in San Francisco Bay Area wastewater.
Weak evidence.
Caveats
The comparison spans a very wide range (roughly 4% to several hundred percent of the median measured loading) because of unreliable use-concentration inputs; this is an environmental-loading estimate, not a personal health-exposure estimate.
Source: Balan 2024, Environmental Science & Technology Link to this fact
Health effects / Animal study
In ex vivo real human and mouse skin (not a lab-grown skin model), plastic nanoparticles only penetrated when they were smaller than about 1 micrometer, and human skin let slightly more through than mouse skin at that size, likely because human hair follicles are larger.
Weak evidence: Single primary study (Song et al. 2024) as read by this review; ex vivo excised tissue, not living skin measured during real use; no real-use cosmetic dose.
Source: Menichetti et al. 2025, Journal of Xenobiotics Link to this fact
Health effects / Measured in people or real products
Almost half (44%) of patients in the founding irritable larynx syndrome series related their symptom onset to a viral illness, most often not a simple upper respiratory infection but herpes zoster, Epstein-Barr virus, viral meningitis, Lyme disease, or post-viral chronic fatigue syndrome.
Weak evidence.
Caveats
Retrospective patient-recalled association, not confirmed causally; n=39, one clinic; the paper's own abstract says "one third", which its own Results text ("almost half") and Table 4 (17/39=43.6%) contradict.
Health effects / Review of other studies
Citronella oil, marketed as a natural insect repellent, has been banned in the European Union and Canada since 2006, partly because it contains methyl eugenol, which the US National Toxicology Program considers 'reasonably anticipated to be a human carcinogen' based on animal studies.
Weak evidence.
Caveats
No human carcinogenicity data exist for methyl eugenol; this is a regulatory ban and an animal-based NTP classification relayed by a secondary review, not measured harm from using citronella products.
Source: Ramsey 2020 (YJBM), Yale Journal of Biology and Medicine Link to this fact
Health effects / Review of other studies
No published study has been found that tests whether quaternary ammonium compounds specifically from laundry fabric softeners or dryer sheets, as opposed to disinfectant or cosmetic-preservative exposure, cause asthma or skin sensitization in consumers.
Weak evidence: This is an evidence-gap statement, not a positive finding; the review also never discusses esterquats, the ester-linked chemistry that dominates modern fabric softeners, at all.
Source: Peyneau 2022, Frontiers in Toxicology Link to this fact
Health effects / Review of other studies
Estimated prevalence of multiple chemical sensitivity across the reviewed epidemiological literature ranges from about 1% to more than 15% of the population, a spread the review attributes to diagnostic difficulty, lack of standardized case-definition criteria, and differing recognition of the condition across countries.
Weak evidence.
Caveats
Secondhand synthesis of several distinct primary studies with different case definitions and populations, not a single standardized measurement; the review does not report the underlying studies' individual case definitions in enough detail to weight the range.
Source: Rossi 2018, Journal of Occupational & Environmental Medicine Link to this fact
Health effects / Review of other studies
A cohort of laborers acutely exposed to gasoline vapors above allowed limits during an underground tunnel-excavation job later developed symptoms similar to those reported in multiple chemical sensitivity, and the study authors argued the workers' sociocultural profile made simple psychosomatic suggestibility an unlikely sole explanation.
Weak evidence.
Caveats
Cited secondhand from Davidoff et al. (primary study not yet in our evidence base); occupational cohort with no independent control for pre-existing chemical sensitivity, and "unlikely to be suggestible" is the original authors' qualitative judgment, not a tested exclusion of a psychological contribution.
Source: Rossi 2018, Journal of Occupational & Environmental Medicine Link to this fact
Health effects / Review of other studies
Some solvents can theoretically sensitize the heart muscle to the body's own adrenaline-type hormones, raising a theoretical risk of arrhythmia or cardiac arrest under chemical exposure in people with multiple chemical sensitivity.
Weak evidence.
Caveats
Cited from a toxicology reference textbook (Olson, Acute Intoxications, Poisons, Pharmaceutical Substances and Drugs), not from any MCS-specific study; the review's own authors state this risk "has not been detected in any epidemiological study so far." Mechanistic/theoretical only.
Source: Rossi 2018, Journal of Occupational & Environmental Medicine Link to this fact
Health effects / Self-reported survey
In the same MCS patient sample, an anxiety-depressive symptom cluster (anxiety, palpitations, depression, sleep disturbance, chest tightness) was statistically distinct from, and less prevalent than, the hyperosmia/asthenia and respiratory clusters, leading the authors to call for more study of the psychosomatic aspects of MCS.
Weak evidence: Cross-sectional, no control group; cannot show whether anxiety-depressive symptoms are a cause, a consequence, or a comorbidity of MCS; see contradictions register C45.
Source: Del Casale 2020 Link to this fact
Health effects / Review of other studies
A review of MCS mechanism studies describes hyperosmia (heightened smell sensitivity from a lowered odor-detection threshold) as common in multiple chemical sensitivity, and cites a small brain-imaging study where MCS patients showed stronger brain responses than healthy controls specifically at odor-recognition-threshold and normal-perceived odor levels.
Weak evidence.
Caveats
Secondhand summary of a single small study (Azuma et al. 2016, 12 patients/7 controls) not independently read or verified in this evidence base; runs counter to other reviews' claim that MCS patients have normal odor thresholds.
Source: Palmieri et al. 2020, Reviews on Environmental Health Link to this fact
Health effects / Review of other studies
Small studies cited in this review report MCS patients have lower catalase and glutathione S-transferase (GST) enzyme activity than healthy controls, potentially impairing detoxification of chemical substances.
Weak evidence: Secondhand from a single research group's studies (De Luca et al.), not independently verified; enzyme-activity differences do not establish that they cause MCS symptoms.
Source: Palmieri et al. 2020, Reviews on Environmental Health Link to this fact
Health effects / Self-reported survey
In a small lab study, MCS patients exposed to increasing concentrations of the odorant n-butanol reported more intense odors, had higher heart rates, and reported more symptoms over time than healthy controls, with no difference in respiratory rate or skin conductance.
Weak evidence: Secondhand from a single study (Andersson et al. 2016, 18 patients/18 controls) not independently read; small single-lab sample.
Source: Palmieri et al. 2020, Reviews on Environmental Health Link to this fact
Health effects / Measured in people or real products
A case report found a woman with a gain-of-function mutation in the Nav1.7 sodium channel (SCN9A gene) had unusually high olfactory sensitivity along with very low pain, thermal, and tactile thresholds in the nose and lower legs, showing a genetic mechanism can raise smell sensitivity and pain sensitivity together.
Weak evidence: A single case report (one 50-year-old woman); cannot establish how common this mechanism is among MCS patients generally, who mostly do not carry this specific mutation.
Source: Palmieri et al. 2020, Reviews on Environmental Health Link to this fact
Health effects / Review of other studies
A review proposes that TRPV1 and TRPA1, chemical-sensing nerve receptors in the nose, airway, and elsewhere, become upregulated and sensitized (a lower threshold and bigger response to normally tolerated triggers) in both neurodegenerative disease and multiple chemical sensitivity, following long-term exposure to air pollution, oxidative stress, and inflammation.
Weak evidence.
Caveats
Narrative, not systematic review; mechanism is a synthesis of others' receptor biology, oxidative-stress, and imaging studies, not new experimental data; shares its primary capsaicin-challenge evidence base with Molot 2023 (a single small, unreplicated Gothenburg research lineage).
Source: Molot 2022, Reviews on Environmental Health Link to this fact
Health effects / Review of other studies
People with multiple chemical sensitivity do not show the brain-mass loss or olfactory-nerve damage seen in neurodegenerative diseases such as Alzheimer's or Parkinson's; instead, brain-imaging studies find altered processing of odors without evidence of nerve damage, while trigeminal-nerve sensitization is the feature specific to MCS.
Weak evidence.
Caveats
Based on a qualitative present/absent/unknown comparison table (the review's Table 2) built by the authors, not a quantitative meta-analysis; no inter-rater or per-cell sourcing detail given.
Source: Molot 2022, Reviews on Environmental Health Link to this fact
Health effects / Review of other studies
A clinical allergist's practice review proposes that idiopathic environmental intolerance (IEI, formerly multiple chemical sensitivity) commonly involves a genetic anxiety/panic-disorder predisposition and a classically conditioned pairing of specific odors with physiologic sympathetic arousal, citing IEI patients' panic-like responses to sodium lactate infusion and CO2 inhalation challenges and an elevated frequency of a panic-disorder-associated cholecystokinin B receptor allele in a pilot study.
Weak evidence.
Caveats
Built almost entirely on the same author's own small, largely unreplicated 1990s-2000s pilot studies from one Toronto clinic; the paper does not cite or engage the TRPV1/TRPA1 capsaicin-cough-hypersensitivity evidence for a peripheral biological mechanism.
Source: Binkley 2023, Journal of Allergy and Clinical Immunology: In Practice Industry-funded Link to this fact
Health effects / Measured in people or real products
In a small genetic study of 6 people with multiple chemical sensitivity and 5 controls, every single MCS patient carried at least one rare, homozygous variant in a gene from the SLC "solute carrier" transporter family, compared to only 1 of 5 controls.
Weak evidence.
Caveats
Single unreplicated pilot cohort (n=11 total); at least 8 uncorrected statistical comparisons across four gene groups; no odds ratios or effect sizes reported for any variant; no independent replication cohort tested.
Source: Alcorta & Gomez-Diaz 2025, International Journal of Molecular Sciences Link to this fact
Health effects / Test-chamber measurement
In a controlled chamber study, 11 asthmatics with documented bronchial hyperreactivity who breathed a 25 milligram per cubic meter mixture of 22 indoor/occupational VOCs for about 85 minutes had their lung function (FEV1) fall to 90.7% of their pre-exposure baseline, a significant drop from their own baseline.
Weak evidence.
Caveats
The 90.7%-of-baseline decline, while significant vs. the subject's own baseline (p<0.05), was not significantly different from the decline seen after sham (clean-air) exposure (97.4% of baseline); single small study, not independently replicated.
Source: Harving et al. 1991, American Review of Respiratory Disease Link to this fact
Health effects / Test-chamber measurement
The size of the FEV1 decline during the 25 mg/m3 VOC exposure tracked each asthmatic subject's baseline bronchial hyperreactivity to histamine: the more hyperreactive the person, the larger the lung-function drop.
Weak evidence: Secondary correlation analysis within a single small study (n=11); not independently replicated.
Source: Harving et al. 1991, American Review of Respiratory Disease Link to this fact
Health effects / Test-chamber measurement
Breathing the VOC mixture did not change asthmatic subjects' bronchial reactivity to histamine afterward, and no delayed (late-phase) breathing symptoms appeared in the following 24 hours at any dose tested.
Weak evidence: Single small study; absence of a late reaction in 11 subjects over one exposure each does not rule out delayed effects with repeated or prolonged exposure.
Source: Harving et al. 1991, American Review of Respiratory Disease Link to this fact
Health effects / Test-chamber measurement
In a controlled human chamber study, 14 healthy young men who breathed a 25 milligram per cubic meter mixture of 22 everyday indoor VOCs for 4 hours showed a significant increase in nasal inflammatory cells (neutrophils) compared to breathing filtered air, both right after exposure (roughly 2-fold, read from a chart) and, more strongly, 18 hours later (roughly 8-9-fold, read from a chart).
Weak evidence.
Caveats
Single small study (n=14, one lab); a much larger, later study using the identical outcome measure (nasal-lavage neutrophils) at a similar dose (Laumbach et al. 2005, n=130) found no change at all, an unresolved contradiction. The full-cohort magnitude figures are approximate, read from a bar chart, not printed numbers.
Source: Koren et al. 1992, Archives of Environmental Health: An International Journal Link to this fact
Health effects / Test-chamber measurement
A subgroup analysis restricted to the 9 subjects with a low pre-exposure baseline neutrophil count found the same pattern on exact, table-reported numbers: nasal neutrophils rose from 1.4 to 16.0 (times 10,000 cells) immediately after VOC exposure and to 67.6 eighteen hours later, versus no comparable rise after breathing filtered air.
Weak evidence: Small subgroup from a single small study; not independently replicated.
Source: Koren et al. 1992, Archives of Environmental Health: An International Journal Link to this fact
Health effects / Test-chamber measurement
The nasal-inflammation response to the VOC mixture was concentrated in a small number of high-responder subjects (4 of 14), while about half the group (7 of 14) showed minimal or no response to the same exposure — consistent with survey findings that only a minority of people report sensitivity to indoor VOCs.
Weak evidence.
Caveats
Individual-subject pattern from a single small study; the authors themselves note it would need to be tested by re-exposing the same high-responder subjects a second time to see if the response is consistent.
Source: Koren et al. 1992, Archives of Environmental Health: An International Journal Link to this fact
Health effects / Self-reported survey
Most of these patients (7 of 10) were already using asthma inhalers or inhaled steroids for their symptoms and reported getting little or no relief from them.
Weak evidence.
Caveats
Small, uncontrolled self-report within a 10-patient case series; consistent with a later, larger figure (8 of 12) from the same research group's 2000 paper and with an independent Canadian clinic's finding on a related condition, but this 1998 figure alone is not a controlled medication-response trial.
Source: Millqvist, Bende & Löwhagen 1998, Allergy Link to this fact
Health effects / Animal study
After three exposures to one fabric-softener brand, mice showed mild lung inflammation (small clusters of white blood cells and fluid buildup in the walls of air sacs) with no eosinophils, but the difference from sham-exposed mice in lung-tissue density and lung weight was not statistically significant.
Weak evidence.
Caveats
The study's own authors describe the finding as 'very mild'; not shown to be dose-dependent, and the quantitative tissue and weight measures did not differ significantly from controls.
Source: Anderson & Anderson 2000, Journal of Toxicology and Environmental Health, Part A Link to this fact
Health effects / Other evidence
People with allergies (atopic, by skin-prick test) showed a significantly larger drop in a small-airway lung-function measure (FEF25-75) than non-atopic people after the highest VOC exposure (50 mg/m3), suggesting they may be somewhat more physiologically sensitive to VOC mixtures at high doses.
Weak evidence.
Caveats
Very small subgroup (n=5 atopic); atopy was not associated with symptom reports or with any other measured outcome, so this does not show that fragrance/VOC respiratory reactions are generally allergic.
Source: Pappas et al. 2000, Int J Occup Environ Health 6:1-8 Link to this fact
Health effects / Lab study (cells or chemistry)
In vitro, the preservative benzalkonium chloride (BAK) — but not latanoprost or timolol at an intraocular-relevant 1:1000 dilution — dramatically increased human lens epithelial cell secretion of PGE2, IL-1alpha, and IL-6 at concentrations as low as 0.2 micrograms/mL (about 0.5 micromolar, a 1000-fold dilution of typical topical eye-drop strength).
Weak evidence.
Caveats
Single unreplicated in vitro study relayed secondhand in this editorial (primary data is Goto et al. 2003, not yet its own evidence base page); actual intraocular BAK concentrations achieved in patients are unpublished, so the clinical relevance of the tested doses is uncertain.
Source: Brandt 2003, citing Goto et al. 2003 (same issue), Archives of Ophthalmology Industry-funded Link to this fact
Health effects / Other evidence
In cultured human trabecular meshwork cells, BAK concentrations as low as 0.00002% — well below the 0.005-0.02% range found in commercial glaucoma drops — significantly reduced cell density and cell growth.
Weak evidence.
Caveats
Single in vitro study; bovine trabecular meshwork cells in a different study required about 50x that concentration (0.001%) to show the same effect, so results vary by species and cell state.
Source: Rasmussen et al. 2014, citing Samples et al. 1989, Journal of Ocular Pharmacology and Therapeutics Industry-funded Link to this fact
Health effects / Measured in people or real products
In the same chamber study, particles formed when the citrus fragrance chemical d-limonene reacted with ozone tended to shift that same heart-rhythm marker in the opposite direction from candle smoke, at particle levels similar to everyday cleaning or air-freshener use.
Weak evidence.
Caveats
This tendency was not statistically significant on its own versus clean air (HF -7.2%, p=0.41); only its difference from candle smoke's opposite-direction change reached significance (p=0.02, 12-subject paired comparison). Not replicated.
Source: Hagerman et al. 2014, Atmospheric Environment Link to this fact
Health effects / Lab study (cells or chemistry)
BKC aerosol exposure altered secretion of 166 proteins in bronchial epithelial cells (84 up, 82 down); a gene-disease network of the upregulated secreted proteins linked GDF15, MMP1, and VEGFA (each increased two- to three-fold) to atherosclerosis and cardiovascular disease, suggesting inhaled BKC could have a direct, not just stress-mediated, systemic cardiovascular effect.
Weak evidence.
Caveats
This is a novel hypothesis from one cell-culture secretome analysis cross-referenced against disease-association databases (DisGeNET, CTD), not a measured blood biomarker change in an exposed animal or human; the authors describe it as warranting further investigation.
Source: Kim et al. 2025, Ecotoxicology and Environmental Safety Link to this fact
Health effects / Review of other studies
A trained Labrador retriever accurately identified cancer patients by sniffing their exhaled breath and stool samples in a controlled study.
Weak evidence: Single trained-dog study cited secondhand; not independently replicated at scale in this review.
Source: Kippenberger 2012, Experimental Dermatology Link to this fact
Health effects / Hypothesis
A 2019 minireview proposes that frequent, long-term burning of scented candles in poorly ventilated rooms may increase bladder cancer risk, based on chemicals in candle emissions (PAHs, benzo[a]pyrene, formaldehyde, phthalates) that are separately linked to bladder cancer via occupational and other non-candle exposure routes.
Weak evidence.
Caveats
No case-control, cohort, or biomonitoring study has ever tested candle use against bladder cancer; the authors' own conclusion calls for that study to be done. This is a narrative minireview with no original data.
Source: Adamowicz 2019, Cancer Prevention Research Link to this fact
Health effects / Review of other studies
Formaldehyde, an ingredient of candle fragrances with a low boiling point, is released at high concentration during candle burning, but the authors state there is no known mechanism linking formaldehyde to bladder carcinogenesis.
Weak evidence: Association is explicitly postulated, not mechanistic, per the authors' own text.
Source: Adamowicz 2019, Cancer Prevention Research Link to this fact
Health effects / Review of other studies
Higher urinary MEHHP (a DEHP phthalate metabolite) was correlated with increased urothelial cancer risk in patients with chronic kidney disease; phthalate esters have also been identified in synthetic candle fragrances.
Weak evidence: Single cohort restricted to chronic kidney disease patients, not the general population; not a candle-exposure study; secondhand citation of Huang & Chou 2018.
Source: Adamowicz 2019, Cancer Prevention Research Link to this fact
Health effects / Review of other studies
Benzyl salicylate, BHT, and butylphenyl methylpropional, all found in the tested perfumes, have been shown in other cited research to interfere with estrogenic signaling pathways and may therefore increase breast cancer risk.
Weak evidence: No doses or a quantified risk estimate are given; this is a mechanistic association from cited literature, not a measured increase in breast cancer risk from perfume use.
Source: Tegengif 2022 Link to this fact
Health effects / Lab study (cells or chemistry)
Lilial is extensively metabolized by liver enzymes (via a Phase I cytochrome P450 route) into lysmerylic acid and p-tert-butylbenzoic acid; the study's authors propose that the metabolite p-tert-butylbenzoic acid, not Lilial itself, is the more likely driver of Lilial's reproductive-toxicity classification, since that metabolite is separately reported (in other cited studies) to disrupt lipid metabolism in sperm-producing tissue.
Weak evidence.
Caveats
This is the authors' own proposed explanation built on citation of two other papers (Laue 2020, Hareng 2023, neither yet in this evidence base); the reprotoxic mechanism of the metabolite was not itself tested in this paper.
Source: Jablonská 2023, Sci Rep 13:18536, Scientific Reports Link to this fact
Health effects / Other evidence
A case report describes a 66-year-old woman diagnosed with exogenous lipoid pneumonia after inhaling vaporized paraffin from burning candles.
Weak evidence: Single case report; not generalizable evidence of population-level risk.
Source: Nazir et al. 2024, Annals of Medicine & Surgery Link to this fact
Health effects / Other evidence
A screening-level model of a heavy occupational scented-candle exposure (aromatherapy workers, 8 hours a day for 40 years) found a 95th-percentile lifetime lung cancer risk from PAHs alone of 1.20 in a million, marginally exceeding the commonly used 1-in-a-million risk threshold, under the single worst combination of low ventilation and intermediate humidity tested.
Weak evidence.
Caveats
PAH-only estimate (excludes co-emitted benzene, formaldehyde, and particulate matter that would add to total risk); occupational 8h/day/40-year exposure scenario, not typical home candle use; single candle formulation and small chamber; only the 95th-percentile Monte Carlo estimate under the single worst condition exceeded the threshold, not the mean case.
Health effects / Animal study
Ancestral exposure of pregnant rats to the fungicide vinclozolin (100-200 mg/kg/day, by injection) has repeatedly produced reduced sperm count and motility and increased ovarian cysts in the great-grandoffspring generation across several studies from one laboratory, but two industry-linked studies using oral (rather than injected) maternal exposure during the same developmental window found no transgenerational effect at all.
Weak evidence.
Caveats
The negative replication studies (Schneider et al., 2008 and 2013) are affiliated with BASF, a chemical manufacturer, and used a different exposure route (oral vs. intraperitoneal injection) and possibly different effective dose than the positive studies, so route/dose and funding source are both plausible explanations for the disagreement; unresolved as of this review.
Health effects / Animal study
In rats, daily skin application of six commercial perfumes (three original, three counterfeit) for 28 days significantly increased mast cell counts in the liver and in several lung compartments (perivascular, peribronchial, pleural) compared to untreated controls, with no allergic or inflammatory tissue damage seen on routine histology.
Weak evidence.
Caveats
Single animal study (n=12/group Wistar rats), not replicated; effects were inconsistent across the two special stains used and not every perfume produced a statistically distinguished result in every tissue; perfumes were not chemically characterized.
Source: Hananeh 2021, Open Veterinary Journal Link to this fact
Health effects / Animal study
Neither original nor counterfeit perfume increased mast cell numbers in rat skin (the site of direct application) or the heart after 28 days of daily use — the systemic organs (liver, lungs) responded, not the local application site.
Weak evidence.
Caveats
Counterintuitive given topical exposure; the study did not investigate a mechanism (e.g., systemic absorption vs. distant mast cell recruitment) for why the application site itself was unaffected.
Source: Hananeh 2021, Open Veterinary Journal Link to this fact
Health effects / Animal study
The counterfeit perfume F3 produced the largest single effect in this rat study (liver mast cells rose about 13-fold over control, from about 25 to about 319 cells/mm2 by toluidine blue stain), but the other two counterfeit perfumes tested (F1, F2) did not clearly exceed their genuine counterparts on most measures.
Weak evidence.
Caveats
Only 3 counterfeit/genuine pairs tested, purchased from local markets with no independent authentication or chemical fingerprinting of counterfeit status; not a general fake-vs-genuine comparison.
Source: Hananeh 2021, Open Veterinary Journal Link to this fact
Health effects / Measured in people or real products
The only study in this review to measure parabens and PCOS together (39 PCOS women across normal-weight and obese subgroups, 20 controls) found comparably low plasma paraben levels in all groups and no significant association with PCOS.
Weak evidence: One small study; absence of an association in this one reproductive-endocrine endpoint does not establish that parabens have no hormonal effects generally.
Health effects / Review of other studies
Two studies of urinary triclosan and PCOS point in opposite directions: a 2019 study of 123 women (40 PCOS, 83 controls) found no association, while a 2018 study cited in the same review's discussion found PCOS women had significantly higher urinary triclosan and an elevated LH/FSH ratio, with higher triclosan associated with increased odds of PCOS.
Weak evidence: Both are small, single-population, cross-sectional studies; the review counts only the null one among its 15 primaries and does not explain why the positive study was excluded.
Health effects / Other evidence
In two of three reported chemical-intolerance case studies, QEESI Chemical Intolerance and Symptoms scores fell substantially after a home intervention that reduced fragrance and other VOC sources (Case 1: 80→43 and 63→23; Case 3: 74→54 and 59→23, each on a 0-100 scale).
Weak evidence.
Caveats
Open-label, no control group or blinding, cases selected for notable improvement (not representative of the full 37-patient cohort), and symptom change could reflect counseling/expectation effects rather than VOC reduction specifically.
Source: Rincón et al. 2024, Primary Health Care Research & Development Link to this fact
Health effects / Review of other studies
Urinary octocrylene (a UV filter) was significantly associated with PCOS, but only in women with a BMI of 24 kg/m2 or higher (adjusted OR=1.512, 95% CI: 1.043-2.191); benzophenone-3 and homomethyl salicylate showed no association.
Weak evidence: Based on a single Chinese case-control study (Gu et al. 2019); not replicated; no association found or tested in normal-weight women.
Health effects / Review of other studies
The one study testing parabens against PCOS found no association between summed paraben exposure and PCOS.
Weak evidence: Single small study (19 PCOS women, 20 controls); does not rule out effects of individual parabens or other outcomes.
Health effects / Review of other studies
The evidence on triclosan and PCOS is inconclusive: one Chinese study found infertile women with PCOS had significantly higher urinary triclosan than infertile women without PCOS (p=0.0407), while a second Chinese study recruiting from the same hospital in the same period found no association and triclosan below detection in nearly all samples.
Weak evidence.
Caveats
The two studies directly conflict and overlap in recruiting hospital and window (Zhejiang University Women's Hospital, March 2014-August 2015); the null study also found BPA, benzophenone-3, and homomethyl salicylate below detection where other studies in the same review detect them, suggesting a possible assay-sensitivity issue in that study.
Health effects / Other evidence
Assuming a finite, realistic 10 microliter/cm2 application (rather than the undiluted infinite dose actually tested), the study estimated that about 23% of an applied dose of propylene glycol and about 9% of dipropylene glycol would be absorbed through human skin over 24 hours.
Weak evidence.
Caveats
Extrapolated estimate, not a measurement under finite-dose conditions; the authors themselves flag it as an overestimate, and note the propylene glycol (MPG) figure may be further inflated by stratum-corneum retention that occurs under infinite dosing but would not occur at a finite dose.
Source: Fasano 2011, Toxicology in Vitro Industry-funded Link to this fact
Health effects / Self-reported survey
In a small Takasago-funded study of 131 healthy German adults, those exposed nightly for two weeks to a custom fragrance blend reported modestly better self-rated sleep quality than an unscented control group, but wearable sleep trackers found no actual difference in sleep.
Weak evidence.
Caveats
N=38 vs 19 control; non-randomized, preference-selected groups; industry-funded and co-authored with a Takasago employee; no true placebo (sham-odor) control; effect not sustained after exposure stopped.
Source: Li et al. 2025, Scientific Reports Industry-funded Link to this fact
Information, not medical advice. See also: myths we won’t tell you.