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.
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 / Self-reported survey
In this Atlanta sample, women were reported as chemically hypersensitive at roughly 1.75 times the rate of men (about 15.7% of women vs 8.95% of men, wiki arithmetic from the paper's cross-tabulation), a smaller sex skew than the same authors' national survey found (F:M about 4.0).
Weak evidence.
Caveats
Our arithmetic, not stated by the authors; the primary brief gives sample counts of 926 women / 600 men and 71.7/28.3% sensitive, which implies roughly 15.3% vs 9.3% (F:M about 1.6), not the 905/592 denominators behind 1.75; single regional self-report survey.
Source: Caress & Steinemann 2003 (EHP), Environmental Health Perspectives 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 / Measured in people or real products
A 2025 global disease-burden model estimates that DEHP exposure from plastics was linked to about 356,000 cardiovascular deaths worldwide in 2018 (about 13.5% of CV deaths among 55-64-year-olds), and about 10.5 million years of life lost.
Weak evidence.
Caveats
A disease-burden model that applies one hazard ratio from a single earlier US cohort (the same group's); that ratio (1.10) is the all-cause estimate in the source cohort, whose CV-specific DEHP estimate was only borderline; assumes causation. Bloomberg Philanthropies (anti-plastics campaign) funded.
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
Health effects / Self-reported survey
Diffusing a scent in the bedroom air was linked to better self-reported sleep quality and less next-day tiredness than a pillow spray or no scent at all, in a small industry-funded trial of healthy adults, but this has not been shown to improve sleep as measured objectively.
Weak evidence.
Caveats
N=39 diffuser vs 19 control; one of the two reported p-values (0.052) is above the paper's own significance threshold; non-randomized; no air-quality/VOC measurement of what the diffuser actually released; funded by Takasago Europe.
Source: Li et al. 2025, Scientific Reports Industry-funded Link to this fact
Health effects / Other evidence
Dermatologists consider moisturizer use critical for preventing and treating numerous skin conditions, and regard allergic or irritant contact dermatitis as the only established health risk of moisturizer use.
Weak evidence.
Caveats
This is the study authors' Discussion-section opinion, not a result of the underlying label survey, and not a formal quantitative risk-benefit analysis weighing skin-barrier/disease-prevention benefits against contact-dermatitis risk. It also covers moisturizers only — no equivalent risk-benefit statement for sunscreen specifically (weighing skin-cancer prevention against contact-dermatitis risk) was found in our evidence base or in this pass, so the video's sunscreen half of the claim remains unsupported by our evidence.
Health effects / Self-reported survey
In the same study, migraineurs with interictal olfactory hypersensitivity (IOH, 16/113) had markedly LOWER rates of osmophobia (75% vs 98%, P=.002) and odor-triggered crisis (68% vs 93%, P=.001) than those without IOH, but markedly HIGHER rates of phantosmia (25% vs 1%, P=.001) and cacosmia/euosmia (18% vs 0%, P=.002) — the opposite direction from the positive IOH-osmophobia association reported by Demarquay et al. 2006.
Weak evidence.
Caveats
Small IOH subgroup (n=16), single study, directly contradicts an earlier primary (Demarquay 2006, not yet in this evidence base); the authors themselves call the discrepancy unexplained and note their IOH question differs from Demarquay's validated chemical odor intolerance index.
Source: Fornazieri 2016, Headache: The Journal of Head and Face Pain Link to this fact
Health effects / Other evidence
Nail salon workers have reported elevated rates of headaches, respiratory irritation, skin problems, and nasal/airway symptoms in prior cross-sectional surveys, consistent with (but not directly tested by) this study's indoor air quality measurements.
Weak evidence: This paper measured air chemistry only, not health outcomes; the symptom literature it cites is cross-sectional survey data from other studies.
Source: Pavilonis, Roelofs & Blair 2018, citing prior nail-salon worker surveys, Journal of Occupational and Environmental Hygiene Link to this fact
Health effects / Other evidence
The TVOC and PM2.5 increases measured after cleaning in this study (up to about 104 ppbv and 14.5 micrograms per cubic meter) fall at the lower end of ranges reported elsewhere for cooking (10-560 ppbv, 0.3-480 micrograms per cubic meter) and smoking (up to 600 ppbv, up to 253 micrograms per cubic meter).
Weak evidence.
Caveats
The cooking/smoking numbers are secondhand citations from other studies, not measurements from this paper, and the authors note their own small-surface controlled experiments likely understate real-world cleaning exposure (e.g., multiple surfaces cleaned in succession, as in the hotel).
Source: Souza 2025, ACS Earth Space Chem, ACS Earth and Space Chemistry Link to this fact
Health effects / Review of other studies
In one study, (R)-(-) and (S)-(+) linalool at concentrations below participants' own detection threshold — undetectable, not perceived as different — produced opposite heart-rate and mood changes, the one result in Herz's 18-study review that offers direct evidence for a chemical (pharmacological) rather than a learned-association mechanism.
Weak evidence.
Caveats
Single study, not independently replicated; per the Kuroda primary the heart-rate difference is significant versus water but the mood difference is significant only between the two forms, not versus water; 7 analyzed subjects; undetectability checked by questionnaire only. Herz's overall conclusion still favors the psychological account for the other 17 studies.
Source: Kuroda et al. 2005, via Herz 2009, International Journal of Neuroscience Industry-funded Link to this fact
Health effects / Review of other studies
A 2004 review in the Journal of Applied Toxicology proposed, as a hypothesis, that parabens in underarm and body care products might contribute to breast cancer, and stated that no causal link is proven.
Weak evidence: Narrative review with no new data; the question is the title; the second author's lab supplies much of the paraben data.
Source: [[src-2004-endocrine-disrupters-estrogenic-chemicals-body-care-cosmetics|Harvey & Darbre 2004]], Journal of Applied Toxicology Link to this fact
Health effects / Review of other studies
Breast cancer researchers reviewing the evidence in 2004 said the link between paraben-containing body care products and breast cancer needed rigorous testing, because tumor detection, cell tests, and rodent studies cannot show human causation.
Weak evidence: Authors' own framing; the review lists Bradford-Hill criteria as a plan, not as applied.
Source: [[src-2004-endocrine-disrupters-estrogenic-chemicals-body-care-cosmetics|Harvey & Darbre 2004]], Journal of Applied Toxicology Link to this fact
Health effects / Review of other studies
Two studies on underarm products and breast cancer disagreed in 2002-2003: one with 813 cases and 793 controls found no association with antiperspirant use, the other, of 437 women already diagnosed, linked heavier use to earlier diagnosis.
Weak evidence: Both secondhand; the second had no cancer-free comparison and measured age at diagnosis, not risk; neither tested parabens.
Source: [[src-2004-endocrine-disrupters-estrogenic-chemicals-body-care-cosmetics|Harvey & Darbre 2004]], Journal of Applied Toxicology Link to this fact
Health effects / Hypothesis
A 2004 review noted that breast tumors are disproportionately found in the upper outer quadrant and left breast and suggested, conditionally, that underarm product use might explain it, with no data presented.
Weak evidence: Conditional suggestion ("if this cannot be explained by … anatomical differences"); not tested in the review.
Source: [[src-2004-endocrine-disrupters-estrogenic-chemicals-body-care-cosmetics|Harvey & Darbre 2004]], Journal of Applied Toxicology Link to this fact
Health effects / Other evidence
In the same study, lavender and neroli themselves had no significant effect on heart rate, skin conductance or self-rated mood, so the calming, or stimulating response followed what people were told, not which scent was present.
Weak evidence: Underpowered (about 10 per cell, HR SDs 4-8 bpm); a null result is not proof of no odor effect; the placebo odor was perceptible (intensity 2.83/7).
Source: Campenni 2004, Psychological Reports Link to this fact
Health effects / Other evidence
The study's authors calculated that PPD loads of 22-939 nmol per hand (about 0.06-2.29 nmol/cm2 averaged over a 410 cm2 hand) exceed a calculated acceptable non-sensitizing area dose of 0.57 nmol/cm2 but are below experimental sensitization (9.3 nmol/cm2 NOEL) and elicitation (28 nmol/cm2) thresholds, and they argue repeated daily exposure may still be enough to sensitize or elicit allergy.
Weak evidence: Authors' extrapolation from hand averages; no sensitization outcomes were measured; real dose is unevenly distributed and likely higher in places.
Source: Lind et al. 2005, The Annals of Occupational Hygiene Link to this fact
Health effects / Measured in people or real products
In a small Japanese lab study, breathing a very faint jasmine tea or lavender odor for 5 minutes lowered heart rate by about 3 beats per minute for 40 minutes more than breathing water did.
Weak evidence: About 10 analyzed adults (24 recruited across two experiments), no blinding described, single lab, authors from a tea company; effect sizes about, read from Fig. 1.
Source: Kuroda et al. 2005, European Journal of Applied Physiology Industry-funded Link to this fact
Health effects / Measured in people or real products
One mirror-image form of linalool, (R)-(-), lowered heart rate by about 2.7 beats per minute, while the other form, (S)-(+), raised it by about 1.7, at a concentration the volunteers said they could not smell.
Weak evidence.
Caveats
Seven analyzed subjects; aqueous concentration 0.03 ppm, not measured air level; 'could not smell' rests on a questionnaire; values about, read from Fig. 4; no replication in our evidence base.
Source: Kuroda et al. 2005, European Journal of Applied Physiology Industry-funded Link to this fact
Health effects / Measured in people or real products
In that study parabens were spread fairly evenly across the breast from armpit to sternum; only n-propylparaben was modestly higher near the armpit (P = 0.010 across regions), and no other paraben showed a pattern.
Weak evidence: Small gradient (the authors say so), no correction for the many statistical tests run, and blanks for n-propylparaben were large in one assay batch.
Source: [[src-2012-measurement-paraben-concentrations-breast-tissue-serial-locations|Barr 2012]], Journal of Applied Toxicology Link to this fact
Health effects / Measured in people or real products
Paraben levels in the breast tissue did not track where the tumor was, whether the tumor was estrogen-receptor positive, the woman's age, or how long she had breast-fed.
Weak evidence: Small sample, tissue taken after diagnosis (cancer may start years earlier), and tumor tissue itself was not tested.
Source: [[src-2012-measurement-paraben-concentrations-breast-tissue-serial-locations|Barr 2012]], Journal of Applied Toxicology Link to this fact
Information, not medical advice. See also: myths we won’t tell you.