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 / Review of other studies
In a small double-blind, randomized lab test (Ternesten-Hasséus 2002, the primary study behind this review's capsaicin-challenge claim), 12 people with multiple chemical sensitivity coughed significantly more than 12 matched healthy controls at every capsaicin dose tested (P<0.05 to P<0.005), a sign that their airway irritant nerves are oversensitive.
Moderate evidence.
Caveats
Now confirmed by reading the primary source directly rather than only via this review's secondhand paraphrase: n=12 patients vs 12 matched controls, single Gothenburg clinic, MCS diagnosed only by Cullen's clinical criteria (no independent biomarker), and not independently replicated outside this same research group (which has authored nearly every paper in this specific evidence line).
Source: Molot 2023, Neuroscience and Biobehavioral Reviews Link to this fact
Health effects / Lab study (cells or chemistry)
In lab studies, common flavor and fragrance chemicals act directly on TRPA1, the nerve receptor that senses irritants such as mustard oil: cinnamon's cinnamaldehyde and thyme's thymol switch it on, while camphor and eucalyptus oil block it.
Moderate evidence: Cell and animal pharmacology; the review's framing is therapeutic, not hazard.
Source: Mihara & Shibamoto 2015, Allergy, Asthma & Clinical Immunology Link to this fact
Health effects / Review of other studies
Salicylate fragrance chemicals pass through skin and are converted in the body to salicylic acid, the compound aspirin becomes: for methyl salicylate (wintergreen), human studies found roughly 12-30% of an applied dose absorbed.
Moderate evidence.
Caveats
Human absorption data are almost all for methyl salicylate, often under occlusion at pharmaceutical concentrations; the review quotes the range three different ways (2-43%, 12-30.7%, 11.8-30.7%).
Source: RIFM Expert Panel / Belsito 2007, Food and Chemical Toxicology Industry-funded Link to this fact
Health effects / Self-reported survey
Many people with chemical sensitivities delay or avoid medical care because clinics and hospitals are heavily scented; healthcare was named as one of the least accessible settings (31 of 60).
Moderate evidence: Qualitative, self-selected Canadian sample; frequency of care avoidance not quantified.
Source: Roy 2026 Link to this fact
Health effects / Measured in people or real products
Sunlight can turn some fragrance chemicals into skin allergens: the now-banned perfume ingredient 7-methoxycoumarin made 11 of 25 volunteers photoallergic, and in people already sensitized, 0.001% plus UVA light triggered a reaction.
Moderate evidence: Artificial UVA at 20 J/cm2 (~1 h summer sun) for the 0.001% figure; predictive photomaximization test; ingredient banned in EU cosmetics since 2000.
Source: SCCNFP 2000 Link to this fact
Health effects / Self-reported survey
In a national survey of 1,098 Australian adults, 6.5% said a doctor or health professional had told them they have multiple chemical sensitivities, and 18.9% said they are unusually sensitive to everyday chemicals.
Moderate evidence: Single self-reported 'ever told' item, online panel, adults 18-65; a South Australian population survey found 1% diagnosed; same dataset as the AU fragrance reports.
Source: Steinemann 2018, Preventive Medicine Reports Link to this fact
Health effects / Self-reported survey
Among Australians who said they had been diagnosed with multiple chemical sensitivities, 91.5% reported health problems from fragranced products such as air fresheners, scented cleaners, and other people's perfume.
Moderate evidence: N = 71; self-report; partly built into the definition.
Source: Steinemann 2018, Preventive Medicine Reports Link to this fact
Health effects / Self-reported survey
In a 2016 US national survey, 86% of people who said a doctor had diagnosed them with multiple chemical sensitivity reported health problems from fragranced products, most often breathing problems (50%), migraines (47%) and eye/nose symptoms (47%).
Moderate evidence: Self-report; 'diagnosed' = told by any health professional; opt-in online panel; same dataset as Steinemann 2016.
Source: Steinemann 2018 (JOEM), Journal of Occupational and Environmental Medicine Link to this fact
Health effects / Self-reported survey
In the same 2016 US survey, about 1 in 4 adults (25.9%) said they were unusually sensitive to everyday chemicals such as cleaning products, perfume, and detergents, and 81% of them reported health problems from fragranced products.
Moderate evidence: Self-report; adults 18-65 in an opt-in online panel; earlier US telephone surveys gave 11-16%.
Source: Steinemann 2018 (JOEM), Journal of Occupational and Environmental Medicine Link to this fact
Health effects / Measured in people or real products
In a small double-blind lab test, 12 people with multiple chemical sensitivity coughed significantly more than 12 healthy matched controls every time they inhaled capsaicin (the compound that makes chili peppers hot), and the difference grew larger at higher doses.
Moderate evidence: N=12 vs 12, single Gothenburg clinic, MCS diagnosed only by Cullen's clinical criteria (no independent biomarker), not independently replicated outside this research group.
Source: Ternesten-Hasséus 2002, Journal of Occupational and Environmental Medicine Link to this fact
Health effects / Measured in people or real products
The extra coughing in multiple chemical sensitivity patients was not explained by asthma or classic allergy: patients tested negative on standard allergy skin-prick and methacholine airway-reactivity tests, and lung function (FEV1) did not change after capsaicin, pointing to an oversensitive airway nerve response rather than an allergic or asthmatic reaction.
Moderate evidence.
Caveats
Small single-center sample; several patients used asthma/allergy medication for symptom control (withheld before testing), so baseline airway status over time is not fully independent of treatment.
Source: Ternesten-Hasséus 2002, Journal of Occupational and Environmental Medicine Link to this fact
Health effects / Measured in people or real products
Non-Hispanic Black women douched far more often than white women (39% vs 13% in the past month) and had significantly higher blood 1,4-dichlorobenzene, a possible contributor to racial differences in chemical exposure.
Moderate evidence: Association, not a demonstrated causal pathway; unadjusted racial comparison for the biomarker figure.
Source: Ding 2020, Journal of Women's Health Link to this fact
Health effects / Measured in people or real products
Using the identical question and instrument in the same Swedish town, adults report being bothered by strong odors about twice as often as teenagers (33% vs 15.6%), and objectively confirmed sensory hyperreactivity is about seven times more common in adults (6.3% vs 0.9%), suggesting chemical sensitivity often develops with age rather than being present from childhood.
Moderate evidence.
Caveats
Cross-sectional age comparison across two separate studies (not a longitudinal cohort); the adult comparator (Johansson 2005/2006) is cited secondhand and is not yet a primary source in our evidence base.
Source: Andersson 2008, International Journal of Hygiene and Environmental Health Link to this fact
Health effects / Lab study (cells or chemistry)
Three fragrance and cosmetic chemicals used in bodycare products applied around the breast, benzyl salicylate, benzyl benzoate, and butylphenylmethylpropional (Lilial), activated the human estrogen receptor and increased growth of estrogen-dependent breast cancer cells in a laboratory dish, an effect blocked by an anti-estrogen drug, suggesting the mechanism runs through the estrogen receptor.
Moderate evidence.
Caveats
Independent, non-industry-funded MCF7 cell study; concentrations required were 10,000 to 3,000,000-fold higher than the estradiol positive control, and none of the three compounds produced a full agonist response within 7 days (partial agonists at that timepoint, converging toward full over 35 days). No animal or human confirmation exists for any of the three compounds. A 2023 independent, guideline-validated retest of Lilial alone (OECD/EPA HeLa9903 ER-transactivation and MDA-kb2 AR-transactivation reporter assays, up to 100 µM, including its major Phase I S9 metabolites) found no estrogenic or androgenic agonist activity at all; this does not test benzyl salicylate or benzyl benzoate, and uses a different (receptor-transactivation vs. proliferation/pS2) endpoint, so it complicates but does not retract this finding for Lilial specifically.
Source: Charles & Darbre 2009, Journal of Applied Toxicology Link to this fact
Health effects / Lab study (cells or chemistry)
These estrogen-receptor effects only appeared at concentrations tens of thousands to millions of times higher than the natural hormone estradiol needs to produce the same size effect, this is laboratory-dish evidence that these chemicals can act like a weak estrogen, not evidence that normal skin or cosmetic use delivers enough of them to the breast to do so.
Moderate evidence.
Caveats
The exposure comparison is our own back-of-envelope calculation, not in the paper, using the fragrance industry's own worst-case 100% dermal-absorption assumption for benzyl salicylate only; benzyl benzoate and Lilial have no systemic-exposure estimate in our evidence base at all, so no comparable check exists for them.
Source: Charles & Darbre 2009, Journal of Applied Toxicology Link to this fact
Health effects / Measured in people or real products
In the nasal-lavage arm of the same 130-woman chamber study, breathing a VOC-ozone mixture containing citrus and pine scent chemicals (limonene, alpha-pinene) caused no significant increase in nasal irritation symptoms or in objective inflammation markers (immune cells, IL-6, IL-8, protein) in nasal fluid.
Moderate evidence.
Caveats
Single 2-hour exposure in healthy, non-asthmatic, non-chemically-sensitive women; a different, smaller earlier study using a different lavage technique found a positive result at a similar VOC dose.
Source: Laumbach 2005, Journal of Occupational and Environmental Medicine Link to this fact
Health effects / Measured in people or real products
In a small double-blind lab test, a drug that numbs sensory nerves (lidocaine) cut in half the number of coughs that chemically sensitive patients had after inhaling capsaicin, evidence that their airway sensitivity runs through nerve pathways rather than the kind of airway narrowing seen in asthma.
Moderate evidence.
Caveats
N=12, single Gothenburg clinic, same research lineage as most other evidence base capsaicin-challenge studies; the same lidocaine blockade also works in healthy subjects (cited within the paper), so it shows the pathway exists, not that it is disease-specific.
Health effects / Review of other studies
Across 6 independent lab studies using a forced-choice 'which one is the real chemical?' test, people who report multiple chemical sensitivities were not better than other people at telling active chemical exposures apart from blank or sham ones.
Moderate evidence.
Caveats
A systematic review, not new data; the 6 studies span different research groups, chemicals, and blinding tiers but are heterogeneous (worker cohorts, clinic patients, different named subgroups pooled together).
Source: Das-Munshi 2006, Journal of Allergy and Clinical Immunology Link to this fact
Health effects / Self-reported survey
In a large random sample of Swedish adults (Vasterbotten, n=3,406), 12.2% said they get symptoms from odorous or pungent chemicals such as perfumes and cleaning agents in doses that don't bother most other people, but only 3.3% had actually been given a doctor's diagnosis of a chemical-intolerance condition.
Moderate evidence: Single region (Vasterbotten county), not national; diagnosis status is itself self-reported, not verified against medical records.
Source: Palmquist 2014, International Journal of Hygiene and Environmental Health Link to this fact
Health effects / Self-reported survey
People who report being intolerant to one environmental factor (chemicals, certain buildings, electromagnetic fields, or everyday sounds) are far more likely than chance to also report intolerance to another — for example, self-reported chemically intolerant Swedes were about six times more likely than average to also report building-related symptoms (observed 96 vs. 19.5 expected under chance).
Moderate evidence: Cross-sectional single-item design; cannot separate a shared physiological mechanism from a shared symptom-reporting/attribution style or shared exposure circumstances.
Source: Palmquist 2014, International Journal of Hygiene and Environmental Health Link to this fact
Health effects / Measured in people or real products
In a lab EEG study, people who scored high on a validated chemical-sensitivity questionnaire showed brainwave (ERP) evidence of difficulty disengaging attention from a pungent gas (CO2) and an odorant (amyl acetate) specifically, not from a neutral tone, when told to ignore them and focus on another task.
Moderate evidence.
Caveats
Single lab study, n=21 chemically sensitive vs 17 nonsensitive Swedish adults defined by one self-report questionnaire (CSS-SHR), not a clinical MCS diagnosis; not independently replicated; ERP habituation comparison across only two session halves is a crude proxy per the authors' own caveat.
Source: Andersson 2009, Journal of Psychosomatic Research Link to this fact
Health effects / Measured in people or real products
The same chemically sensitive group did not habituate to repeated chemical exposure over 1.5 hours (perceived intensity of CO2 and an ERP amplitude marker stayed flat), while a nonsensitive comparison group habituated normally on both measures.
Moderate evidence.
Caveats
Small single-lab sample (n=21/17, fewer after ERP exclusions); the CS group is defined by a questionnaire cutoff, not a clinical diagnosis; sensitization was chemosomatosensory (CO2)-specific and did not extend to the olfactory (amyl acetate) magnitude-estimation measure.
Source: Andersson 2009, Journal of Psychosomatic Research Link to this fact
Health effects / Review of other studies
A family of temperature- and chemical-gated TRP ion channels spans the range of stimuli relevant to breathing: TRPV2 detects tissue-damaging heat (>=52C), TRPV1 detects warmth/capsaicin/low pH/ethanol (>=42C), TRPV3/TRPV4 detect normal ambient temperature and osmotic/mechanical changes (roughly 22-40C), TRPM8 detects menthol and cool temperatures (8-22C), and TRPA1 detects very cold temperatures, mustard oil, garlic isothiocyanates, and THC (below 8C) but not menthol.
Moderate evidence: This is a conceptual/diagrammatic synthesis of previously published receptor characterization studies, not new data generated in this paper.
Source: Baraniuk & Merck 2009, Annals of the New York Academy of Sciences Link to this fact
Health effects / Review of other studies
A systematic review of 27 human chemical-exposure challenge studies on multiple chemical sensitivity (1998-2015) found no scientific consensus on whether the reaction is physical (toxicological) or psychological: only a minority of studies concluded toxicological causation, a similar minority concluded psychological causation, and the single largest group of studies reached no conclusion at all.
Moderate evidence.
Caveats
Narrative bibliographic review, not a PRISMA-registered systematic review; no formal quality scoring of the 27 underlying studies, which used heterogeneous designs (facemask aerosol, exposure chamber, sticks, bottle, dynamic olfactometer) and small samples (as few as 8 per arm); classification into toxicological/psychological/no-conclusion groups is the review authors' own qualitative judgment, not a quantitative synthesis.
Source: Rossi 2018, Journal of Occupational & Environmental Medicine Link to this fact
Health effects / Review of other studies
Across 13 independent qualitative studies from four countries, people with multiple chemical sensitivity consistently describe being kept out of everyday places by scented/chemical products, and losing jobs, income, or social relationships because of it.
Moderate evidence.
Caveats
Systematic review of qualitative (not survey) evidence; meta-aggregation of 53 findings from 13 small, mostly clinic/support-group/self-selected-website-recruited studies (sample sizes 4-203), none rated top quality by the review's own NICE checklist. Converges in direction with, but does not quantitatively confirm, Steinemann's self-report survey percentages already in our evidence base.
Source: Driesen 2020, Journal of Psychosomatic Research Link to this fact
Health effects / Test-chamber measurement
Telling people a real chemical exposure is a harmful industrial solvent versus a beneficial natural extract changed how irritating they rated identical 800 ppm acetone air and how many health symptoms (throat/nasal irritation, lightheadedness, nausea, drowsiness) they reported afterward, even though every group breathed the same concentration.
Moderate evidence: Single lab, single cohort, not independently replicated; co-funded by the Chemical Manufacturers' Association alongside NIH grants (coi/industry-funded).
Source: Dalton et al. 1997, Int Arch Occup Environ Health 69:407-417 Industry-funded Link to this fact
Health effects / Measured in people or real products
In a small Swedish clinic study, people whose breathing symptoms were triggered by scents and chemical irritants — but who had normal lung function and negative allergy and asthma tests — coughed much more after inhaling capsaicin (the hot-pepper compound) than either people with verified asthma or healthy volunteers (93 vs 23 average coughs at the highest dose, P<0.001).
Moderate evidence.
Caveats
Small (n=10 per patient group, n=28 healthy controls), single-clinic study; capsaicin dosing was open-label (patients not told doses would increase) rather than placebo-blinded, so it is a correlational patient-vs-comparator design, not an intervention.
Source: Millqvist, Bende & Löwhagen 1998, Allergy Link to this fact
Health effects / Measured in people or real products
The extra coughing in these chemically sensitive patients could not be explained by asthma: their lung function, methacholine reactivity, and skin-prick allergy testing were all normal, yet they still coughed dose-dependently to inhaled capsaicin, and even to a plain saline control, while a separate group of people with verified asthma did not cough more than healthy volunteers.
Moderate evidence.
Caveats
Single small clinic sample (n=10 per patient group); normal methacholine and skin-prick tests were inclusion criteria for the chemically sensitive group, not an independent finding in an unselected population.
Source: Millqvist, Bende & Löwhagen 1998, Allergy Link to this fact
Health effects / Government agency
As of 1998, EPA's own environmental-health office stated that certain types of childhood cancer were increasing but the causes were largely unknown, and that the agency lacked a reliable basis to determine whether most untested high-production-volume industrial chemicals were safe or unsafe for children.
Moderate evidence.
Caveats
A general statement about data gaps as of 1998, not a study establishing or ruling out any specific chemical-childhood-cancer link; the paper explicitly states EPA does not know how many, if any, childhood cancers are caused by these exposures.
Source: Goldman 1998, Environmental Health Perspectives Link to this fact
Health effects / Self-reported survey
People with asthma were about 4 times more likely to report a doctor's diagnosis of environmental illness/multiple chemical sensitivity than people without asthma (19.0% vs. 4.6%), and over twice as likely to self-report unusual sensitivity to everyday chemicals (31.5% vs. 13.9%).
Moderate evidence.
Caveats
Cross-sectional association from a single population survey with no independent replication cited here; does not establish that asthma causes or is caused by chemical sensitivity, only that they co-occur more than chance in self-report.
Source: Kreutzer, Neutra & Lashuay 1999, American Journal of Epidemiology Link to this fact
Health effects / Self-reported survey
Women were about 1.6 times more likely than men to self-report sensitivity to more than one everyday chemical, after adjusting for other factors, though doctor-diagnosed MCS itself was not significantly associated with sex.
Moderate evidence.
Caveats
Single population survey; unadjusted sex ratios for this item (F:M ~2.3) sit well below the ~4:1 ratio later found in a national survey using the same question wording, so the sex effect size varies by sample.
Source: Kreutzer, Neutra & Lashuay 1999, American Journal of Epidemiology Link to this fact
Health effects / Self-reported survey
Reports of doctor-diagnosed multiple chemical sensitivity and self-reported chemical sensitivity were spread fairly evenly across race/ethnicity, income, education, marital status, and geography in a representative California sample, unlike clinic-based case series which have reported a predominance of middle- to upper-class white women.
Moderate evidence.
Caveats
Homogeneous distribution is consistent with either a real physiologic mechanism or widespread cultural apprehension about chemicals; the study explicitly does not distinguish between these explanations.
Source: Kreutzer, Neutra & Lashuay 1999, American Journal of Epidemiology Link to this fact
Health effects / Other evidence
Methacrolein activates the sensory-irritant receptor by chemically reacting with it (like acrolein), not by simple physical adsorption, and its carbon-carbon double bond — not its aldehyde group — is the key reactive feature; it is roughly six times less potent than acrolein itself.
Moderate evidence: Mechanistic inference from a potency-ratio comparison across compounds tested in different (cited) studies, not a direct receptor-binding assay.
Source: Larsen & Nielsen 2000, Toxicology Letters Industry-funded Link to this fact
Health effects / Animal study
In the same study, a cotton tee-shirt that had already been dried with a fabric-softener pad — not the pad itself — still emitted enough residual chemical to cause significant sensory irritation in mice (49% of breaths, versus 6% for an unwashed new shirt), at a much lower bulk air concentration (86 ppm) than the raw pad's headspace.
Moderate evidence.
Caveats
Single lab, one brand tested, n=8 exposed mice; airflow limitation (7%, not significant except in 1 of 8 mice) and pulmonary irritation were not significantly changed from the new-shirt control.
Source: Anderson & Anderson 2000, Journal of Toxicology and Environmental Health, Part A Link to this fact
Health effects / Lab study (cells or chemistry)
In a lab test, four common fragrance/flavor chemicals found in essential oils – citral, geraniol, nerol, and trans-anethole – weakly activated the human estrogen receptor, and eugenol weakly blocked it, but all needed concentrations 100,000 to 1,000,000 times higher than the body's own estrogen to show any effect.
Moderate evidence: Single-lab yeast reporter assay, confirmed by direct receptor-binding but not by a second cell-based assay (Ishikawa cells, negative for all compounds).
Source: Howes et al. 2002, Journal of Pharmacy and Pharmacology Link to this fact
Health effects / Lab study (cells or chemistry)
Linalool and eucalyptol (1,8-cineole) – two of the main scent chemicals in lavender and tea tree oil – showed no estrogen-receptor activity at all in this yeast test, alongside 14 other common essential-oil constituents that were tested and found inactive.
Moderate evidence.
Caveats
Single assay type (yeast ERE reporter); does not test androgen-receptor activity or steroid-synthesis enzymes, which other studies show linalool and eucalyptol can affect differently.
Source: Howes et al. 2002, Journal of Pharmacy and Pharmacology Link to this fact
Health effects / Self-reported survey
In a 2002-03 US national telephone survey of 1,054 randomly selected adults, 11.2% self-identified as unusually sensitive to everyday chemicals such as cleaning products, perfume, and detergents, and 2.5% said they had been medically diagnosed with multiple chemical sensitivity (MCS).
Moderate evidence.
Caveats
Single national random-digit-dial telephone survey; self-report with no clinical verification of hypersensitivity or diagnosis; the earliest in a cross-country series of self-report chemical-sensitivity prevalence figures.
Source: Caress & Steinemann 2003, Archives of Environmental Health: An International Journal Link to this fact
Health effects / Self-reported survey
Among the 11.2% of US adults who self-identified as chemically hypersensitive, about 2 in 3 (66.7%) described their symptoms as severe or moderately severe, and about 1 in 7 (13.2%) said they had lost a job because of it; 72.7% had changed their household or personal-care products.
Moderate evidence: Self-report severity and lifestyle-effect items in a subgroup of n=117-122; no clinical verification.
Source: Caress & Steinemann 2003, Archives of Environmental Health: An International Journal Link to this fact
Health effects / Self-reported survey
In this national survey, women were reported as chemically hypersensitive at roughly 4 times the rate of men (about 15.9% of women vs 4.0% of men, wiki arithmetic from the paper's cross-tabulation), and prevalence rose steadily with age from about 7% under age 36 to about 15% over age 50.
Moderate evidence.
Caveats
Sex- and age-specific prevalence rates are evidence base arithmetic from the paper's Table 4 cross-tabulation, not stated directly by the authors; single national self-report survey.
Source: Caress & Steinemann 2003, Archives of Environmental Health: An International Journal Link to this fact
Health effects / Self-reported survey
In a 1999-2000 telephone survey of 1,582 randomly selected adults in the Atlanta, Georgia metro area, 12.6% self-identified as unusually sensitive to everyday chemicals, and 3.1% reported a medical diagnosis of environmental illness or multiple chemical sensitivity (MCS).
Moderate evidence: Single regional random-digit-dial telephone survey; self-report with no clinical verification of hypersensitivity or diagnosis.
Source: Caress & Steinemann 2003 (EHP), Environmental Health Perspectives Link to this fact
Health effects / Self-reported survey
Among Atlanta-area adults who reported chemical hypersensitivity, about 1 in 7 (13.5%) said they had lost a job because of it (1.8% of the entire sample), and about 3 in 10 (29.9%) said it made shopping in stores difficult.
Moderate evidence.
Caveats
Self-report, single regional survey; per the primary brief (Caress & Steinemann 2004, Table 1) these items were asked of 'yes' plus 'not sure' respondents (denominators 214-215), not only the 199 'yes'.
Source: Caress & Steinemann 2003 (EHP), Environmental Health Perspectives Link to this fact
Health effects / Self-reported survey
In the same follow-up, the most common symptoms reported after a chemical exposure were headache (88.4%) and burning eyes (76.8%), followed by asthma-like breathing difficulty (59.4%) and nausea or stomach distress (55.1%).
Moderate evidence.
Caveats
Small, non-random follow-up sample (n=69); self-reported symptoms with no clinical verification; the symptom-question cluster had the lowest internal-consistency score (Cronbach's alpha 0.5054) of the three question clusters tested.
Source: Caress & Steinemann 2003 (EHP), Environmental Health Perspectives Link to this fact
Health effects / Measured in people or real products
In a PET brain-imaging study of 12 women with multiple chemical sensitivity (MCS) and 12 matched controls, MCS subjects activated the brain's core odor-processing regions (amygdala, piriform, and insular cortex) LESS than controls when smelling most odorants, not more, despite resting brain activity being normal in both groups.
Moderate evidence: N=12/group, women only, single center (Karolinska), no independent replication of this exact PET paradigm in our evidence base yet.
Source: Hillert et al. 2007, Human Brain Mapping Link to this fact
Health effects / Measured in people or real products
In a double-blind chamber study of 130 healthy women, those who scored high on a validated chemical-odor-intolerance questionnaire did not have worse symptoms, stress-hormone (cortisol) levels, or cognitive/driving-simulation performance when exposed to an indoor VOC or VOC-plus-ozone mixture, compared to women who scored low on the same questionnaire.
Moderate evidence.
Caveats
Single lab, subsample of 130 (40 high-CI, 46 low-CI, tertile split); healthy, non-smoking women only; people with clinically significant MCS/illness behavior were excluded, and the authors could not recruit volunteers at the extremes of chemical intolerance; one 140-minute exposure, not repeated or chronic exposure.
Source: Fiedler 2008, Psychosomatic Medicine Link to this fact
Health effects / Measured in people or real products
Women prone to negative affect (anxiety, worry, distress) became more anxious after a public-speaking stressor during an indoor-chemical exposure session, regardless of what was in the air (clean air, VOCs, or VOCs plus ozone) – but they did not show higher cortisol or more physical (non-anxiety) symptoms than women low in negative affect.
Moderate evidence.
Caveats
Tertile-split subsample (45 high-NA, 48 low-NA) of 130 healthy women; excludes people with diagnosed psychiatric conditions; a public-speaking task is a milder stressor than daily-life stress.
Source: Fiedler 2008, Psychosomatic Medicine Link to this fact
Health effects / Measured in people or real products
People who scored high in chemical intolerance or negative affect rated the same chemical exposure and their own symptoms as more annoying and more distressing than other participants did, even though their measured symptom counts, cortisol, and driving/attention performance were no different.
Moderate evidence: Annoyance/distress were retrospective, subjective 5-point ratings, not the same structured symptom-severity measure used for the main null; single study, healthy women only.
Source: Fiedler 2008, Psychosomatic Medicine Link to this fact
Health effects / Self-reported survey
In the same study, chlorine/bleach exposure (adjusted OR 1.01, 95% CI 0.47-2.18), latex glove use (adjusted OR 0.69, 95% CI 0.32-1.51), and glutaraldehyde exposure (crude OR 1.31, 95% CI 0.53-3.23) showed no significant association with reported asthma; QAC exposure was the only occupational chemical exposure that remained statistically significant after adjustment.
Moderate evidence.
Caveats
A null result in one cross-sectional study does not prove these exposures are safe; some comparisons (e.g. glutaraldehyde, chlorine/bleach) had small exposed groups and wide confidence intervals, so a true effect could have been missed for lack of statistical power.
Source: Gonzalez 2014, Clinical & Experimental Allergy Link to this fact
Health effects / Self-reported survey
Using an expert job-task-exposure matrix, high occupational exposure to formaldehyde (OR 1.33), glutaraldehyde (OR 1.18), hypochlorite bleach (OR 1.18), hydrogen peroxide (OR 1.19) and enzymatic cleaners (OR 1.33, the only one significant at P<0.001) was each associated with poorer asthma control in US nurses, versus low exposure to the same chemical.
Moderate evidence.
Caveats
Exposure levels come from a job-task-exposure matrix built from a separate reference sample's questionnaire responses, not direct measurement; 95% confidence intervals for these specific odds ratios were shown only as graphical whiskers in the source figure, not printed, so are not reported as exact numbers here.
Source: Dumas 2017, European Respiratory Journal Link to this fact
Health effects / Review of other studies
A review of controlled chamber studies (carbon dioxide, ammonia, formaldehyde, sulfur dioxide, glycol/glycol-ether mixtures) found no consistent evidence that people with allergic rhinitis or mild asthma are more sensitive to sensory-irritant chemicals than non-allergic people.
Moderate evidence.
Caveats
The underlying chamber studies excluded moderate and severe asthma/allergy by design and tested mostly non-fragrance irritants; one exception was found (allergic subjects more sensitive to n-propanol specifically), and the review is narrative, not a systematic review with a defined search protocol.
Source: Nielsen & Wolkoff 2017, Regulatory Toxicology and Pharmacology Industry-funded Link to this fact
Health effects / Self-reported survey
The study found no association between childhood or adult hair product or hair oil use and mammographic breast density, a separate, strong breast-cancer risk factor, suggesting that if hair-product chemicals affect breast cancer risk, it may be through pubertal timing rather than breast density.
Moderate evidence: Small sample (N=248) limits power to detect a true but modest effect on breast density; one adult product subgroup (hair dye) did show a small positive association with density.
Source: McDonald 2018, Environmental Health Link to this fact
Health effects / Review of other studies
People with chemical intolerance or multiple chemical sensitivity react more strongly than healthy controls in controlled chamber exposures to irritant chemicals, with derived sensitivity factors typically 1 to 3 times higher and, in some studies, up to about 20 times higher.
Moderate evidence.
Caveats
Objective physiological confirmation was rare across the underlying studies; most of the signal is in subjective symptom ratings, which can be influenced by odor perception and expectation.
Source: Mangelsdorf et al. 2021, Int J Hyg Environ Health, International Journal of Hygiene and Environmental Health Link to this fact
Health effects / Lab study (cells or chemistry)
Among 62 individually tested deodorant ingredients, only fragrance chemicals (plus one insect-pheromone contaminant) showed any estrogenic activity; no carrier, stabilizer, emulsifier, plasticizer, antitranspirant, or other active ingredient (including triclosan and BHT) tested positive.
Moderate evidence: Only 62 of the many ingredients found by GC/MS screening were selected for individual testing, based on frequency of occurrence; ingredients not selected were not tested at all.
Health effects / Review of other studies
Fragrance chemicals have been reported to cause immediate-type contact urticaria, photosensitivity reactions, and rarer miscellaneous effects such as depigmentation and orofacial granulomatosis, but the review characterizes all of these as currently rare and not causing significant clinical problems.
Moderate evidence: Causal relationship for the miscellaneous effects in Table 13 is explicitly stated by the review as "not always established beyond doubt" (mostly case reports).
Source: de Groot 2020, Dermatitis 31(1):13-35, Dermatitis® Link to this fact
Health effects / Lab study (cells or chemistry)
An academic in vitro toxicology screen of Lilial (butylphenyl methylpropional, the fragrance chemical banned from EU cosmetics in 2022) found no cytotoxicity, no mutagenicity in a mammalian gene mutation assay, no nephrotoxicity, and no NF-κB or NRF2 stress-pathway activation, in either Lilial itself or its major liver-generated (S9) metabolites, up to 100 µM.
Moderate evidence.
Caveats
Single academic lab, one round of testing, not yet independently replicated; a genotoxicity endpoint (γH2AX) in the same paper was inconclusive, not clean negative, so 'no adverse effect' does not extend to every endpoint tested.
Source: Jablonská 2023, Sci Rep 13:18536, Scientific Reports Link to this fact
Health effects / Lab study (cells or chemistry)
Using OECD/EPA guideline-validated receptor-transactivation assays (HeLa9903 for estrogen receptor, MDA-kb2 for androgen receptor), Lilial and its major liver metabolites showed no estrogen- or androgen-receptor agonist activity from 1 nM to 100 µM; the study's authors said they were unable to confirm the European Chemicals Agency's earlier suspicion that Lilial is an endocrine disruptor.
Moderate evidence: Single academic lab; this directly conflicts with a weaker, non-guideline finding from a different assay type (MCF7 proliferation) for the same compound — see contradiction.
Source: Jablonská 2023, Sci Rep 13:18536, Scientific Reports Link to this fact
Health effects / Government agency
An international expert working group convened by the World Health Organization and UN Environment Program concluded that close to 800 chemicals are known or suspected to interfere with hormone receptors, hormone synthesis, or hormone conversion, but only a small fraction of them have been tested for whether they actually cause overt endocrine effects in an intact organism.
Moderate evidence.
Caveats
This is a 2012 expert-consensus count covering every kind of suspected endocrine disruptor (industrial chemicals, pesticides, plastics, cosmetic ingredients, natural compounds), not a fragrance-specific count, and the report is now well over a decade old.
Source: WHO/UNEP 2012 Link to this fact
Health effects / Government agency
Animal studies show that mixtures of endocrine-disrupting chemicals can produce additive effects even when every chemical in the mixture is present at a level too low, on its own, to cause any observable effect, meaning many 'individually safe' exposures could add up to a harmful one.
Moderate evidence.
Caveats
Based on animal mixture studies cited in the report; the report itself states there are no data showing how real-world mixtures of hundreds of EDCs at low concentrations actually affect human or wildlife health.
Source: WHO/UNEP 2012 Link to this fact
Health effects / Government agency
Hormone-disrupting chemicals often do not follow a simple 'more dose equals more effect' pattern; some show non-monotonic dose-response curves, so standard toxicology testing at high doses, divided by a safety factor to estimate a low 'safe' dose, may miss real effects that occur only at low doses.
Moderate evidence: This is the report's own methodological critique of standard regulatory toxicology testing, not a finding about any specific chemical.
Source: WHO/UNEP 2012 Link to this fact
Health effects / Other evidence
A widely cited 2012 review (Vandenberg et al.) cataloged many examples of endocrine-disrupting chemicals producing non-monotonic (U-shaped) dose-response curves; an independent 2013 Danish government reanalysis of that same catalog found that 45% of its cited in vitro examples were artifacts of general cell toxicity rather than true hormone-mediated effects, and only 5 of 34 cited in vivo (whole-animal) examples showed clear evidence of a genuine non-monotonic response.
Moderate evidence.
Caveats
Known only secondhand through an industry-funded critique paper with a direct interest in this conclusion; the original Vandenberg et al. 2012 review and the DTU Food 2013 reanalysis should be read as primaries before this is treated as settled.
Source: Lamb et al. 2014, Regulatory Toxicology and Pharmacology Industry-funded Link to this fact
Health effects / Other evidence
The WHO-UNEP 2012 report changed its conclusion on PCBs and DDT causing adrenocortical hyperplasia (Cushing-like adrenal gland disease) in Baltic seals from 'uncertain association' in the WHO's 2002 report to 'sufficient evidence' of a causal link in 2012, without citing any new supporting data, while not addressing contrary findings that tie similar adrenal changes in other marine mammals to chronic stress rather than chemical exposure, and rat studies finding the opposite direction of adrenal effect (atrophy, not hyperplasia) from the same chemicals.
Moderate evidence: From an industry-funded critique paper; the underlying wildlife and rat studies have not yet been read as primaries by this evidence base.
Source: Lamb et al. 2014, Regulatory Toxicology and Pharmacology Industry-funded Link to this fact
Information, not medical advice. See also: myths we won’t tell you.