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.
Laws and loopholes / Other evidence
Scented-candle manufacturers should be required to disclose indoor-pollution and health risks on labels or packaging under new labeling and packaging laws.
Weak evidence: A policy recommendation with no current legal requirement cited; no such disclosure law exists today per this source.
Source: Nazir et al. 2024, Annals of Medicine & Surgery Link to this fact
Skin allergy / Measured in people or real products
Most patients who reacted to oxidized scent chemicals (58%) also had other fragrance allergies or a history of reacting to fragranced products.
Weak evidence: 31 positive patients.
Skin allergy / Measured in people or real products
People without skin disease reacted to oxidized limonene and linalool as strongly as dermatitis patients.
Weak evidence: Small groups (9 controls per comparison after exclusions).
Source: Bråred Christensson 2009, Contact Dermatitis Industry-funded Link to this fact
Skin allergy / Lab study (cells or chemistry)
In lab tests on human skin cells, the oxidized forms of limonene and linalool reshaped the cells' fats in the same way as a classic potent skin allergen (DNFB), a pattern consistent with oxidative stress.
Weak evidence: One cell line, one dose.
Skin allergy / Lab study (cells or chemistry)
In lab tests on reconstructed human skin, oxidized linalool broke down into reactive radicals that bind to skin proteins, which helps explain why linalool becomes an allergen only after it reacts with air.
Weak evidence: Skin model and model thiols; mechanism, not prevalence.
Source: Kuresepi 2020, Chemical Research in Toxicology Link to this fact
Skin allergy / Lab study (cells or chemistry)
In lab tests on human skin cells, the air-oxidized forms of limonene and linalool (the forms that cause fragrance allergy) damaged the fats in cell membranes at concentrations from 100 µM, with oxidized limonene strongest; a possible second route to skin inflammation not yet shown in people.
Weak evidence: Cell line and liposomes only; added iron; real skin doses unknown.
Skin allergy / Measured in people or real products
Once someone is sensitized, patch tests can trigger reactions at low ppm concentrations of oxidized terpene — but the specific 'as low as 1 ppm' figure is for Δ³-carene in older, narratively-reviewed occupational turpentine literature; for the two terpenes that dominate consumer exposure, modern peer-reviewed dose-response studies put the threshold one to two orders of magnitude higher (limonene hydroperoxides: ~24 ppm single patch application, ~140 ppm repeated realistic exposure, ED₁₀ ≈85 ppm; linalool hydroperoxides: ~560 ppm repeated realistic exposure).
Weak evidence.
Caveats
The 1 ppm figure applies to Δ³-carene in historical occupational patch testing, not to limonene or linalool, and its own study design (occlusion, participant numbers) is not given in the citing review. No limonene- or linalool-specific study supports reactions at ~1 ppm.
Source: Karlberg & Lepoittevin 2021, Contact Dermatitis Link to this fact
Skin allergy / Measured in people or real products
All four patients already allergic to oxidized linalool reacted to air-exposed lavender oil on patch testing.
Weak evidence: N=4 pre-selected sensitized patients; fresh oil not tested alongside; elicitation, not sensitization.
Source: Hagvall 2008, Contact Dermatitis Industry-funded Link to this fact
Skin allergy / Review of other studies
A 2007 clinical review reports that oxidized limonene caused positive patch-test reactions in about 2.6% of dermatitis patients in a European study, leading to a call to add oxidized limonene to routine allergy screening.
Weak evidence.
Caveats
Secondary relay of Matura et al. 2006 (not independently read in this evidence base); this is an early statement of a position later found by other groups (e.g. the IVDK) to over-call weak/doubtful reactions as true allergy.
Source: Brasch 2007, Current Opinion in Allergy and Clinical Immunology Link to this fact
Skin allergy / Review of other studies
By 2007, Fragrance Mix II, a newer fragrance patch-test screen, was showing a high and still-rising rate of positive reactions in German clinic data, on top of the original Fragrance Mix I.
Weak evidence.
Caveats
Cites the original FM II validation studies (Frosch et al. 2005) plus an unpublished personal communication (IVDK network) for the 'still increasing in 2007' claim; neither is independently verified here.
Source: Brasch 2007, Current Opinion in Allergy and Clinical Immunology Link to this fact
Skin allergy / Review of other studies
People sensitized to hydrolyzed wheat protein in cosmetics do not necessarily react to intact wheat protein, so they can generally still eat wheat/bread without a reaction.
Weak evidence: Stated in passing in a narrative review, citing a single 2006 study; not itself verified against the primary.
Source: Brasch 2007, Current Opinion in Allergy and Clinical Immunology Link to this fact
Skin allergy / Review of other studies
In one clinic-based dose study, the paraphenylenediamine concentration that elicited at least a weak positive patch-test reaction in 10% of already PPD-sensitized people was 38 ppm, well below the concentrations permitted for hair dyes — raising the question of whether the standard 1% patch-test concentration is itself safe to apply.
Weak evidence: Threshold applies to already-sensitized individuals in one cited dose-response study, not to the general population's exposure risk; relayed secondhand.
Source: Brasch 2007, Current Opinion in Allergy and Clinical Immunology Link to this fact
Skin allergy / Review of other studies
Fragrance is the most common cause of allergic contact dermatitis in the armpit, and deodorants and antiperspirants are a major source of that fragrance exposure.
Weak evidence: Narrative clinical review with no new data of its own; relays a 1982 cosmetic-product survey and later studies not independently re-checked here.
Source: Musicante 2024, Cutis Industry-funded Link to this fact
Skin allergy / Review of other studies
Axillary dermatitis can occasionally be caused by systemic contact dermatitis or symmetrical drug-related intertriginous and flexural exanthema (SDRIFE) rather than direct topical contact allergy; in sensitized patients, eating balsam-of-Peru-rich foods (citrus, chocolate, tomato, certain alcohols) can trigger a flare without any new topical exposure.
Weak evidence: Relayed from isolated case reports; systemic contact dermatitis of the axillae is described as rare.
Source: Musicante 2024, Cutis Industry-funded Link to this fact
Skin allergy / Other evidence
Across three chemical-intolerance case studies with symptom improvement tied to reduced VOC exposure, blood IgE allergy panels for 16 common indoor/outdoor/food antigens did not track or explain the symptom changes, and only 2 of the full 37-patient cohort (5.4%) had elevated antibodies to both dust mite and cockroach allergens.
Weak evidence.
Caveats
Uncontrolled case-series observation; absence of IgE elevation does not rule out other allergic or non-IgE immune mechanisms, and the paper does not test a specific non-allergic mechanism directly.
Source: Rincón et al. 2024, Primary Health Care Research & Development Link to this fact
Skin allergy / Review of other studies
Fragrance causes both irritant and allergic contact dermatitis, among other adverse skin reactions, and fragrances are the most frequent chemicals causing contact dermatitis overall.
Weak evidence.
Caveats
Narrative review statement, not a ranked prevalence study; does not establish that contact dermatitis (from any cause) is the single most common adverse reaction to skincare products in general, only that fragrance is a leading cause of contact dermatitis specifically and that it can be either irritant or allergic.
Source: Pastor-Nieto 2021, Current Treatment Options in Allergy Link to this fact
Skin allergy / Review of other studies
Fragrance chemicals are also used as food flavorings, and dermatologists consider systemic contact dermatitis from fragrance-related food flavorings in fragrance-allergic patients whose eczema does not clear after 6 weeks of full topical fragrance avoidance.
Weak evidence: Clinical management guidance from a narrative review, not a measured ingestion-exposure or prevalence study; does not quantify how often food flavorings are the actual culprit.
Skin allergy / Review of other studies
Certain fragrance and botanical ingredients have been linked to pigmented cosmetic dermatitis (facial hyperpigmentation), reported mainly in Japan in the 1960s-1970s; the condition became rare after 1978 reformulation of the implicated products.
Weak evidence.
Caveats
Relayed from a narrative review's historical summary (citing older Japanese case-report literature, e.g. Nakayama); no prevalence data or systematic count of cases is given, and a companion evidence base source page (src-2020-review-perfume-present-status-associated-allergens) names specific implicated ingredients (ylang-ylang, jasmine absolute, cananga, benzyl salicylate, hydroxycitronellal, sandalwood, geraniol) but the video's decade range (1970s-80s) is only approximately matched (source says 1960s-1970s).
Source: de Groot 2020, Dermatitis 31(1):13-35, Dermatitis® Link to this fact
Skin allergy / Other evidence
The National Eczema Association's Seal of Acceptance certification criteria exclude chemical UV-absorber sunscreens, accepting only physical (mineral) sunscreens containing titanium, zinc, or iron oxide.
Weak evidence.
Caveats
This reflects one certification body's precautionary ingredient-exclusion criteria for eczema-prone skin, not measured comparative allergic-contact-dermatitis incidence rates between mineral and chemical UV filters — no such comparative rate data were found in our evidence base or in this pass. Do not read this as evidence that mineral filters cause fewer ACD reactions in the general population, only that this eczema-focused body's rules treat them as the safer default.
Source: National Eczema Association 2026 Link to this fact
Skin allergy / Review of other studies
Standard fragrance-allergy patch screening (fragrance mix I plus balsam of Peru) is estimated to identify only 60 to 70 percent of people with true fragrance allergy, due to the evolving ingredient mix used by the perfume industry.
Weak evidence: Secondhand figure relayed from the authors' ref. 11 (a NACDG/Scheman source), not independently verified or re-derived in this paper.
Source: Zirwas & Moennich 2008, The Journal of Clinical and Aesthetic Dermatology Link to this fact
What you can do / Measured in people or real products
Childcare rooms with more fresh-air exchange had lower levels of several of the chemicals measured.
Weak evidence: Bivariate correlations, 34 rooms.
What you can do / Measured in people or real products
Keep scented products closed and avoid old, long-opened ones: limonene and linalool became skin irritants after weeks of air exposure.
Weak evidence.
Caveats
Extrapolated from lab-oxidized neat material (10-20 weeks air exposure); product storage not tested by this paper. Two independent industry market surveys have now directly tested the specific mechanism this advice assumes (in-bottle oxidation with age) and both found it absent: Kern 2014 (39 aged fine fragrances + 29 antiperspirants, 9 months accelerated storage) and Natsch 2019 (104 products spanning fine fragrances, antiperspirants, creams, and lotions, including two fine fragrances tracked 3-6 years at room temperature) both found no progressive hydroperoxide accumulation with age, and consumer-product doses 2-4 orders of magnitude below elicitation/sensitization thresholds. Both studies are industry-funded (IDEA consortium: Givaudan, Firmenich, IFF, IFRA) and not independently replicated by a non-industry group, and neither tests essential oils or raw materials (separately known to accumulate hydroperoxide) or every product category. Moved to claims-to-avoid because the specific mechanistic basis for this advice (in-container autoxidation) is now negative in the only two real-product tests that exist, even though the underlying autoxidation chemistry itself, in neat/essential oils, is not disputed. Kern 2014 and Natsch 2019 are both industry studies (Givaudan / IDEA consortium) with Natsch as a co-author on both, so they are not independent replications of each other.
Source: Bråred Christensson 2009, Contact Dermatitis Industry-funded Link to this fact
What you can do / Review of other studies
Old, long-opened scented products are more allergenic than fresh ones, because the scent chemicals oxidize on contact with air.
Weak evidence.
Caveats
Time course is primary for lavender oil (Hagvall 2008: LLNA EC3 36% fresh -> 23% at 10 weeks -> 4.4% at 45 weeks in the same batch), but in neat oil in open lab flasks, not formulated products as stored. Kern 2014 first closed part of this gap (39 fine fragrances + 29 antiperspirants, no accumulation over 9 months accelerated storage); Natsch 2019 extends this to 104 products across more categories (adding limonene, creams, lotions) and to multi-year real-time storage (two fine fragrances tracked 3-6 years at room temperature, no accumulation), plus tests products donated by allergic patients themselves (also negative for hydroperoxide). Downgraded to avoid because the specific claim — that aging/opening itself makes a product more allergenic via in-container oxidation — has now failed two independent, broader industry market surveys with no non-industry evidence on the other side; creams, lotions, and fine fragrances/antiperspirants are covered, though essential oils, raw materials, and other categories remain untested and are not covered by this downgrade. Kern 2014 and Natsch 2019 are both industry studies (Givaudan / IDEA consortium) with Natsch as a co-author on both, so they are not independent replications of each other.
Source: Karlberg & Lepoittevin 2021, Contact Dermatitis Link to this fact
What you can do / Self-reported survey
People affected by fragrance say policies work only with purchasing rules for fragrance-free, low-emission products, staff education, better ventilation, and consequences for repeat violations, enforced like smoke-free rules.
Weak evidence: Participants' and authors' proposals; not tested as an intervention.
Source: Roy 2026 Link to this fact
What you can do / Hypothesis
Air a room or clean it instead of scenting it: non-chemical alternatives such as opening windows and better hygiene are the first step in Klaschka's ten-step hierarchy for reducing fragrance exposure.
Weak evidence: Expert recommendation; not tested in the paper.
Source: Klaschka 2020, Environmental Sciences Europe Link to this fact
What you can do / Review of other studies
If a child develops unexplained breast tissue, tell the doctor about every scented product the child uses or is near, including colognes, baby washes, hair products, and diffusers; stopping them is what the case reports did.
Weak evidence: Practical advice drawn from case reports, not a tested intervention.
Source: Hawkins 2020, Complementary Therapies in Medicine Industry-funded Link to this fact
What you can do / Self-reported survey
People who always or usually used a healthy-product app, read ingredient labels, or looked for eco-friendly labels used hair, skin, and beauty products with somewhat lower EWG hazard ratings, by up to half a point on a 10-point scale.
Weak evidence: Cross-sectional; the rating is built from the same labels, so it cannot see undisclosed fragrance chemicals; no exposure measured.
Source: Barrett 2025, Journal of Exposure Science & Environmental Epidemiology Link to this fact
What you can do / Measured in people or real products
Using less shower product and running the bathroom fan both lower the fragrance-terpene peak: emissions scaled with product amount, and halving ventilation raised the modeled limonene peak from about 375 to 495 ppb.
Weak evidence: Amount-scaling from one person's shower; ventilation effect is modeled; no health outcome measured.
What you can do / Test-chamber measurement
Keeping indoor ozone low (no ozone-emitting 'air purifiers' or ionizers) limits both skin-oil chemistry and fragrance-terpene chemistry indoors, because ozone starts both chains.
Weak evidence: This paper makes no recommendation; the ozone-generator advice comes from Singer 2006, and the ventilation/ozone trade-off is our inference.
What you can do / Review of other studies
If you want to avoid persistent fluorinated ingredients, check cosmetic labels for 'PTFE', 'polytetrafluoroethylene', or names containing 'perfluoro-' or 'polyfluoro-'.
Weak evidence.
Caveats
Namazkar 2024 found INCI names for PFAS ingredients can themselves be ambiguous or incorrect (an apparent isomer mismatch for a silane; an undisclosed shorter chain-length range for a phosphate ester), and found unlabeled residual PFCA impurities in nearly every PFAS-containing cosmetic tested (5 of 6 products), which were far more dermally bioaccessible (43-76%) than the labeled ingredient itself (negligible bioaccessibility). Label-reading is a reasonable screen for intentionally added, correctly-named PFAS but does not detect the unlabeled residual impurities this paper shows can be present and bioaccessible regardless of which PFAS is named.
Source: Jomaa 2024, Journal of the Netherlands Society of Toxicology (JNST) Industry-funded Link to this fact
What you can do / Lab study (cells or chemistry)
Only 6 of 42 perfumes tested were comparatively low in hazardous compounds across ten lab tests, which suggests lower-hazard perfumes can be made.
Weak evidence: Products not named, so consumers cannot identify the cleaner ones; in vitro only.
Source: Morlock & Heil 2025, Journal of Chromatography A Link to this fact
What you can do / Instrument measurement
A filter-only HEPA air purifier kept fine-particle readings near zero after hair and nail products were used together in a small closed room.
Weak evidence: Flow-to-volume ratio far above any real home or salon; VOC removal by the carbon filter not credible for acetone/formaldehyde.
What you can do / Review of other studies
Fragrance-free policies are easier to make work when they start with a needs assessment and an inventory of the cleaning and personal products in use, involve employees in drafting, and agree how violations are handled before launch.
Weak evidence: Lessons from unnamed organizations; no outcome data.
What you can do / Review of other studies
Close fragranced products after use and discard them about a year after opening to limit exposure to oxidized allergens.
Weak evidence.
Caveats
Expert advice; no study tests whether it reduces dermatitis. The assumed mechanism (in-bottle oxidation during storage) has now failed two industry market surveys rather than one: Kern 2014 (fine fragrances, antiperspirants, 9 months accelerated storage) and Natsch 2019 (104 products including creams and lotions, two fine fragrances tracked 3-6 years at room temperature) both found no hydroperoxide accumulation with age or storage time. The advice may still be reasonable for essential oils and raw materials (which do carry hydroperoxide, e.g. lavandin ~220 ug/g), just not via this specific in-bottle mechanism for finished consumer products. Both studies are industry-funded (IDEA consortium: Givaudan, Firmenich, IFF, IFRA) and not independently replicated, and say nothing about essential oils, raw materials, or product categories outside fine fragrances/antiperspirants/creams/lotions. Kern 2014 and Natsch 2019 are both industry studies (Givaudan / IDEA consortium) with Natsch as a co-author on both, so they are not independent replications of each other.
Source: Pastor-Nieto 2021 (Klaschka 2010), Current Treatment Options in Allergy Link to this fact
What you can do / Measured in people or real products
Moisturizers that listed alcohol or 'alcohol denat.' near the top of the ingredient list delivered far more ethanol to a mannequin's nose; products with no listed alcohol gave almost none.
Weak evidence: 16 products, qualitative (Fig. 4, no statistic); ethanol hidden inside 'parfum' is not visible on labels; absolute ethanol doses are disputed.
What you can do / Measured in people or real products
'Agua de violetas' colognes marketed to Hispanic families, including preparations made for babies, are a specific consumer product worth asking about if a young child has unexplained breast growth.
Weak evidence: Based on 2 of 3 case reports from one clinic; not every bottle sold under this name contains lavender oil.
Source: Diaz 2016, Journal of Pediatric Endocrinology and Metabolism Link to this fact
What you can do / Hypothesis
If you already notice fragrance-related symptoms, do not expect awareness alone to change your exposure — most Germans who link their own symptoms to fragrance still use fragranced products at or above the average rate; choosing fragrance-free products and spaces is the step that actually reduces exposure.
Weak evidence: Author's recommendation, drawn from the self-exposure paradox in this survey; not itself tested as an intervention.
Source: Klaschka 2020a, Environmental Sciences Europe Link to this fact
What you can do / Review of other studies
If households switch from fragranced to fragrance-free laundry detergent, modeling suggests dryer-vent limonene emissions across a whole city or state could drop substantially — an estimated 1.58 tons per year for metropolitan Melbourne, or 8.66 tons per year for the state of California.
Weak evidence.
Caveats
This is a modeled extrapolation, not a measurement: it multiplies a mean vent concentration from just 2-6 households (one grab sample each) by census household counts and usage-rate assumptions, with no confidence interval or sensitivity analysis anywhere in the calculation; the Melbourne input is dominated by a single outlier household roughly 11 times the other three.
Source: Goodman, Nematollahi & Steinemann 2020/2021, Air Quality, Atmosphere & Health Link to this fact
What you can do / Review of other studies
Wearable personal chemical-exposure monitors with audible threshold alarms ("eNose"-type devices) are proposed as a future tool to help people track real-time chemical exposure and correlate it with symptom onset, alongside biomarker testing (blood/urine for substances or metabolites) when intoxication is suspected.
Weak evidence.
Caveats
A forward-looking recommendation in the review's discussion/outlook section, not a validated or clinically deployed diagnostic tool; no accuracy, sensitivity, or outcome data for any such device is cited.
Source: Rossi 2018, Journal of Occupational & Environmental Medicine Link to this fact
What you can do / Review of other studies
Because people with MCS describe both a fear of asking for accommodations (risking hostility) and a fear of staying silent (risking worsening symptoms), workplaces and services that proactively offer fragrance-free accommodation without requiring the person to ask remove one source of this dilemma.
Weak evidence.
Caveats
Qualitative theme ('suppressing vs expressing needs', 9 findings/5 studies) describing participants' experience, not a tested intervention; no study in this review evaluated an accommodation policy's effect. Downgraded moderate→weak 2026-09-27 (Jev audit): the accommodation recommendation is an inference, not a finding.
Source: Driesen 2020, Journal of Psychosomatic Research Link to this fact
What you can do / Measured in people or real products
A small trial found that a nasal spray containing hyaluronic acid, used daily for a month, reduced smell-detection thresholds and improved smell-disorder and anxiety questionnaire scores in MCS patients compared with a saline spray.
Weak evidence: Single small trial (29 treated/30 controls per this review's own Table 1) from one research group, not independently replicated; not an approved or established MCS treatment.
Source: Palmieri et al. 2020, Reviews on Environmental Health Link to this fact
What you can do / Review of other studies
For people whose fragrance/chemical reactions have a strong anxiety or panic component, mental-health referral, stress management, relaxation training, graded psychological desensitization to trigger odors, and (if needed) low-dose SSRIs are a recommended management approach, used alongside (not instead of) ruling out and treating any real underlying allergic or respiratory disease.
Weak evidence.
Caveats
The author states outright that research on mental-health treatment efficacy specifically in IEI is limited, because many affected patients decline psychiatric referral; the recommendation rests on case reports and phobia-treatment analogy, not controlled trials in this population.
Source: Binkley 2023, Journal of Allergy and Clinical Immunology: In Practice Industry-funded Link to this fact
What you can do / Test-chamber measurement
Accurate, calibrated information about a real chemical exposure (e.g., explaining that mild effects now do not imply long-term harm) can reduce reported irritation and symptoms compared with giving no information at all.
Weak evidence.
Caveats
Single lab study of naive volunteers under brief controlled exposure; may not generalize to real workplaces, longer exposures, or people who already have symptoms from an exposure. Downgraded to weak 2026-09-28 (Jev audit): the action goes beyond what this paper itself tested.
Source: Dalton et al. 1997, Int Arch Occup Environ Health 69:407-417 Industry-funded Link to this fact
What you can do / Measured in people or real products
People whose breathing symptoms are triggered by scents or chemical irritants, but whose standard asthma tests (spirometry, methacholine challenge) come back normal, can ask a specialist about objective sensory-hyperreactivity testing, such as a capsaicin cough-sensitivity challenge, rather than assuming the symptoms are either undiagnosed asthma or purely psychological.
Weak evidence: Capsaicin cough-challenge testing is a research protocol developed and used mainly by this one Swedish research group, not a routine or widely available clinical test.
Source: Millqvist, Bende & Löwhagen 1998, Allergy Link to this fact
What you can do / Government agency
As of 1998, EPA planned to expand its voluntary consumer-labeling initiative beyond pesticides to labels on household and other consumer products such as cleaning agents and latex paint, aiming to give clearer hazard information, especially for children.
Weak evidence.
Caveats
A stated 1998 plan/intention, not a completed program; the paper does not report whether or how it was implemented, and no fragrance-specific labeling requirement is described anywhere in the paper.
Source: Goldman 1998, Environmental Health Perspectives Link to this fact
What you can do / Review of other studies
Close deodorant containers after use and replace them about a year after opening: two of the most common deodorant fragrances (limonene, linalool) are rated weak allergens fresh but oxidize in air into much stronger sensitizers.
Weak evidence.
Caveats
Klaschka relays this oxidation chemistry from prior studies (Karlberg 1994, Matura 2005, Skold 2008), already in our evidence base; she adds no new dose data of her own. Downgraded to weak 2026-09-28 (Jev audit): the action goes beyond what this paper itself tested.
Source: Klaschka 2012, International Journal of Hygiene and Environmental Health Link to this fact
What you can do / Other evidence
Because the association tracked frequency of use in a dose-response pattern, using fewer personal care products or using them less often is the lowest-regret step for someone concerned about a possible link to lung function.
Weak evidence: The study did not test whether reducing use reverses any effect; this is an inference from an observational dose-response pattern, not a tested intervention.
Source: Dales 2013, Annals of Epidemiology Link to this fact
What you can do / Measured in people or real products
Running an ozone-generating device (an ionizer, or some 'air purifiers') at the same time as using citrus- or terpene-scented cleaning or personal-care products creates the same class of reaction-product nanoparticles studied here; keeping the two apart in time, or ventilating, avoids generating them.
Weak evidence.
Caveats
This study alone did not find a significant health effect from the terpene+ozone arm; the precautionary action is supported by the wider ozonolysis-SOA literature in our evidence base (see transformation-products), not by this study's HRV result in isolation. Downgraded to weak 2026-09-28 (Jev audit): the action goes beyond what this paper itself tested.
Source: Hagerman et al. 2014, Atmospheric Environment Link to this fact
What you can do / Other evidence
Because leave-on skin products with large use amounts (body lotion, fine fragrance) drove the highest modeled fragrance-ingredient exposure in this industry model — not air-care products, which had the highest in-product concentrations but low exposure due to no skin contact — a reasonable consumer heuristic is that layering multiple fragranced skin products likely matters more for aggregate systemic fragrance exposure than using a scented candle or air freshener.
Weak evidence.
Caveats
Derived inference from a single industry model covering 8 ingredients; not validated against measured exposure; does not address inhalation health effects, only relative modeled systemic dose.
Source: Safford 2017, Regulatory Toxicology and Pharmacology Industry-funded Link to this fact
What you can do / Hypothesis
Unlike outdoor air pollutants such as vehicle exhaust, people can directly reduce their exposure to limonene at home by limiting use of strongly limonene-scented personal-care products and household cleaners.
Weak evidence: This is the authors' own inference from a cross-sectional association, not a tested intervention; no randomized avoidance trial has been done, though the authors call for one.
Source: Dales & Cakmak 2019, Environmental Pollution Industry-funded Link to this fact
What you can do / Lab study (cells or chemistry)
People on long-term BAK-preserved eye drops (e.g., for glaucoma or dry eye) with ocular surface concerns may want to ask their prescriber about preservative-free formulations.
Weak evidence.
Caveats
Based on an in vitro cell-culture study, not a clinical trial; supports a conversation with a prescriber, not a self-directed switch, and does not establish that any specific preservative-free product (including the study's own TBE formulation) is proven safer in practice.
Source: Kabashima 2020, Journal of Ocular Pharmacology and Therapeutics Industry-funded Link to this fact
What you can do / Measured in people or real products
Powder laundry detergents had the lowest average common-allergen count of any subgroup surveyed (0.75/product) and contained none of the preservative allergens (MI, BIT, MCI/MI, phenoxyethanol) tracked in this study; their only common allergen was fragrance, present in 3 of 4 products.
Weak evidence: Very small subgroup (n=4); one 2019 US best-seller sample, not necessarily generalizable to all powder detergents.
What you can do / Measured in people or real products
Regularly cleaning a dryer's lint trap and keeping vent ducting short and well-maintained is associated with differences in how much microfiber reaches the outside vent, based on comparing two homes with different dryer ages and duct setups.
Weak evidence.
Caveats
This is a two-home comparison, not a tested intervention — the study did not clean or modify ducting and measure a before/after change, so this is an inference from correlation, not a demonstrated fix.
Source: Kapp & Miller 2020, PLOS ONE Industry-funded Link to this fact
What you can do / Measured in people or real products
Keeping candles away from drafts, fans, open windows, and foot traffic that make the flame flicker can substantially cut soot, fine-particle, and particle-bound PAH exposure, since flame disturbance alone (independent of which candle is burned) was the single largest factor increasing these emissions in this chamber study.
Weak evidence.
Caveats
Based on chamber simulation of flame disturbance via a rotating fan, not a home-scale test of specific draft sources; does not address NOx or formaldehyde exposure, which were unaffected by burn disturbance in this study. Graded weak: what-you-can-do resting on one chamber study.
What you can do / Review of other studies
Because this industry classification describes average sensitization thresholds measured in previously unexposed volunteers, not the much lower doses that can trigger a reaction in someone already allergic, a patch-test-confirmed fragrance-allergic consumer should avoid a flagged chemical entirely rather than assume any low listed concentration is safe for them personally.
Weak evidence.
Caveats
This point is not stated by this paper itself; it follows from this evidence base's existing analysis (register entry C112) of the induction-versus-elicitation gap in fragrance industry risk assessment generally.
Source: Na et al. 2022, Dermatitis Industry-funded Link to this fact
What you can do / Lab study (cells or chemistry)
Patients on long-term BAC-preserved eye drops (e.g., for glaucoma) who have corneal or ocular-surface concerns can ask their prescriber about preservative-free alternatives.
Weak evidence.
Caveats
This is a discussion-with-clinician action, not a claim that BAC-preserved drops are unsafe at typical clinical use; based on an in-vitro model plus prior clinical ocular-surface-disease literature the paper cites, not a clinical trial of this specific outcome. Graded weak (orchestrator): in-vitro, 2-donor study alone.
Source: Umetsu et al. 2024, Graefe's Archive for Clinical and Experimental Ophthalmology Link to this fact
What you can do / Measured in people or real products
People patch-tested positive to isoeugenol or Fragrance Mix I should avoid isoeugenol-containing deodorants entirely rather than relying on IFRA-compliant "low" concentrations, since the current 0.02% cap sits inside the range this study showed can elicit reactions in sensitized users.
Weak evidence: Extrapolated consumer advice from a clinical elicitation study; not itself a tested intervention. Graded weak: what-you-can-do resting on one small ROAT study.
Source: Bruze et al. 2005, Contact Dermatitis Link to this fact
What you can do / Lab study (cells or chemistry)
Choosing a roll-on or stick deodorant instead of a spray from the same product line may reduce exposure to the estrogen-active fragrance ingredients this one lab's testing found concentrated in sprays.
Weak evidence.
Caveats
Rests on a single lab's testing of 25 German products; dispenser-type differences most likely reflect how much fragrance a given carrier formulation needs, not a demonstrated safety difference, and this has not been independently replicated or linked to any human exposure or health outcome.
What you can do / Measured in people or real products
Keeping a scented candle unlit doesn't necessarily stop it from adding VOCs to a room's air — one product in this study off-gassed heavily even unlit, so if you want to avoid a candle's chemical emissions, removing the product from the room (not just leaving it unlit) is what this data suggests actually helps.
Weak evidence.
Caveats
Based on one lab's measurements of six specific products in Korea; whether unlit off-gassing in an actual room reaches similar relative levels to what was measured in this study's small chamber has not been tested here.
Source: Ahn et al. 2015, Journal of Hazardous Materials Link to this fact
What you can do / Review of other studies
Ventilate rooms during and after burning scented candles, and prefer higher-quality or unscented candles over cheap paraffin-based scented ones, as a general precaution against indoor chemical accumulation.
Weak evidence.
Caveats
General precaution suggested by the review authors; rests on this single hypothesis paper's synthesis, not on a study measuring outcomes from these actions, and does not itself establish a bladder-cancer risk reduction.
Source: Adamowicz 2019, Cancer Prevention Research Link to this fact
Information, not medical advice. See also: myths we won’t tell you.