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.
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 / 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 / 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
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
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 / 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 / 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
What you can do / Lab study (cells or chemistry)
Cold-atmospheric-plasma deodorizing devices are an emerging non-chemical, non-fragrance approach to underarm odor control worth watching as an alternative to conventional antimicrobial/fragranced antiperspirants.
Weak evidence.
Caveats
Based on one prototype tested only against cultured bacteria and porcine skin dosed with synthetic odor compounds; no human trial, no skin-safety or allergy testing, and the device generates ozone (a known respiratory irritant) as part of its mechanism.
Source: Bok et al. 2024, Scientific Reports Link to this fact
What you can do / Other evidence
Airing out a room after burning scented candles helps remove residual chemical compounds produced during burning.
Weak evidence: Common-sense ventilation advice; not independently quantified in this editorial or checked against primary ventilation-effect data in this evidence base.
Source: Nazir et al. 2024, Annals of Medicine & Surgery Link to this fact
What you can do / Other evidence
A structured home walkthrough that identifies and removes common VOC sources (mothballs, scented cleaning and personal-care products, candles, garage-stored chemicals) and separates stored chemicals from living space (e.g., moving gasoline/solvents/paints to detached storage) reduced measured indoor VOC levels in the homes studied.
Weak evidence.
Caveats
Professional testing and a trained team delivered this intervention over 5 visits across a year; the paper does not test which individual component (removal vs. substitution vs. new storage vs. counseling) drove the VOC reduction. Evidence is one small uncontrolled case series.
Source: Rincón et al. 2024, Primary Health Care Research & Development Link to this fact
What you can do / Review of other studies
Because diet is the main route of human exposure to BPA and phthalates from food packaging, avoiding microwaving food in plastic, cutting back on canned food, and choosing glass, stainless-steel, or aluminum containers instead of plastic can reduce dietary exposure to these obesogenic chemicals.
Weak evidence.
Caveats
This reduces measured chemical exposure; no trial has tested whether making this switch actually changes body weight or obesity risk in people. The review infers this from exposure routes; it cites no intervention study measuring the reduction.
Source: Dalamaga 2024, International Journal of Molecular Sciences Link to this fact
What you can do / Government agency
A patient with fragrance/chemical sensitivity asking a clinic to have staff avoid fragrance for one scheduled appointment is asking for something narrower than a facility-wide rule, and DOJ's 1995 'usually not reasonable' answer was addressed to the broader framing, not this narrower one.
Weak evidence: DOJ never separately analyzed the narrower, one-appointment request; this is an inference from reading the letter against its own attached correspondence, not a DOJ holding.
Source: DOJ TAL605, 1995 Link to this fact
What you can do / Measured in people or real products
Because this study's own route argument points to prenatal (placental) transfer, not breastfeeding, as the main way synthetic musk fragrance chemicals reach a baby, choosing fragrance-free personal-care and laundry products during pregnancy specifically, not only while breastfeeding, is a plausible way to reduce an infant's earliest musk exposure.
Weak evidence.
Caveats
Inferred from pharmacokinetics (musks' short half-life) and matrix comparisons, not from measured product use or from an intervention study; no study has tested whether reducing a mother's product use lowers her infant's cord-blood or milk musk levels.
What you can do / Measured in people or real products
People who want to reduce systemic absorption of chemical UV filters while FDA's requested toxicology studies remain outstanding can choose mineral sunscreens (zinc oxide or titanium dioxide, the only two actives FDA has found generally recognized as safe and effective) or rely more on sun-protective clothing and shade.
Weak evidence: This is a risk-reduction option, not advice to avoid sun protection; the paper explicitly says its findings do not mean people should stop using sunscreen.
Source: Matta 2020, JAMA Link to this fact
What you can do / Other evidence
People rated real scents (lavender 4.5, neroli 4.3 out of 7) as more mood-changing than a placebo scent (3.0), even though the scent did not change their measured heart rate or mood, so a scent seeming to work is not evidence that the chemical is doing it.
Weak evidence: Single small study; perceived effectiveness is self-report and the authors' interpretation (attribution to odor presence) is theirs.
Source: Campenni 2004, Psychological Reports Link to this fact
What you can do / Other evidence
In the industry model for one fragrance chemical (2-phenylethanol), the highest skin dose per area was under the arms (95th percentile about 5,258 micrograms per cm2, nearly all from deodorants), far above the neck (911) or lips (829).
Weak evidence: Illustrative only; authors cite dermal uptake of this chemical under 10%, so absorbed dose would be lower.
Source: Safford et al. 2015, Regulatory Toxicology and Pharmacology Industry-funded Link to this fact
What you can do / Other evidence
In a lab test, geraniol and eugenol (rose- and clove-type fragrance chemicals) were found on a cotton cloth about 4-5 times lower after 8 hours than after 1 hour, with a small amount still detectable weeks later.
Weak evidence: One lab, a spiked mix of six pure standards (not a perfume), cotton to cotton, n = 3 per time point; fabric concentrations, not exposure.
What you can do / Other evidence
After a spill, release or accidental chemical mixing, such as bleach with acid, leave the area and get airflow testing (spirometry, reversibility or an airway reactivity test) if cough or wheeze persists.
Weak evidence: Advice inferred from case reports; the review gives no doses or incidence for household mixing.
Source: Walters 2020, Occupational Medicine Link to this fact
What you can do / Other evidence
Inclusion Canada argues that because the law requires counseling on alternatives to relieve suffering, safe housing free of smoke and chemical infiltration matters; it says her doctors found such housing would have improved her health and quality of life.
Weak evidence: Advocacy post by an organization, written a year later; not independent reporting. Attribute to Inclusion Canada. The post does not say whether counseling occurred in her case.
Source: Inclusion Canada: Remembering Sophia (advocacy post, Feb 22, 2023; redacted copy), Inclusion Canada blog post Link to this fact
What you can do / Other evidence
A friend with MCS says people with the illness cannot easily get justice because the available tribunals take years, and that recognition of MCS as a disability is rarely enforced.
Weak evidence: Personal view of one person with MCS; compare the survey evidence on accommodation refusals before generalizing.
Source: Chemical Sensitivity Podcast ep. 101, 2026 Link to this fact
What you can do / Review of other studies
Several small randomized trials of probiotics or synbiotics in children with ADHD report symptom improvement, but none enrolled children selected for chemical exposure, so they do not show that gut bacteria carry chemical effects.
Weak evidence: Small trials, some without microbiome measurement; relayed by the review without risk-of-bias scores in the main text.
Source: Wu 2026, Biological Psychiatry Global Open Science Link to this fact
Information, not medical advice. See also: myths we won’t tell you.