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.
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
Information, not medical advice. See also: myths we won’t tell you.