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.
Indoor air / Review of other studies
Scent chemicals released by perfumes and scented products can react with ozone in indoor air to form new pollutants, including formaldehyde and fine particles.
Strong evidence.
Caveats
Formation is well established (Fiedler 2005: 40 ppb O3 + a limonene/alpha-pinene-containing VOC mix -> HCHO 13 -> 40 µg/m³, UFP 2,500 -> 46,000 cm-3; Singer 2006; Rossignol 2013; Destaillats 2006 gives the underlying per-ozone yield). Amounts depend on dose and ozone; the harm at real indoor levels is not shown. A far more rigorous, independent toxicologist review (Wolkoff & Nielsen 2017) reaches the same qualitative chemistry conclusion via its own literature synthesis and adds a quantitative caution: in the two largest human tests to date (Fiedler 2005, n=130; Fadeyi 2015, n=71), the resulting reaction mixture caused no significant airway/eye effects, and its own threshold estimate is that >200 µg/m³ ozone at high limonene would be needed before sensory effects are expected. Cite primaries for numbers.
Source: Alblooshi 2025, Frontiers in Toxicology Link to this fact
Indoor air / Measured in people or real products
In week-long air measurements across 11 European cities, the scent chemicals limonene and alpha-pinene were the compounds most concentrated in homes compared with workplaces (about 4x), attributed to perfumes, cleaning and fragranced products.
Strong evidence: Source attribution by the authors, not measured per product.
Source: Geiss 2011, Atmospheric Environment Link to this fact
Indoor air / Other evidence
Terpene ingredients in scented cleaners, air fresheners, perfumes, colognes and essential oils (limonene, pinene, linalool, linalyl acetate) are listed as ozone-reactive indoor sources that make formaldehyde and tiny particles when ozone is present.
Strong evidence.
Caveats
Table 1 is a literature summary; perfumes and essential oils rest on three chamber citations (Chao 2005, Karamalegos 2005, Shu 1997). No product was measured in this paper and it gives no product-specific numbers.
Source: Weschler 2006, Environmental Health Perspectives Link to this fact
Indoor air / Measured in people or real products
In an office-sized test room with some ozone in the air, a single ordinary spray of perfume, body spray, or hair spray, or a dab of hand lotion, set off a burst of new ultrafine particles within minutes, reaching 34,000–200,000 particles per cubic centimeter, more than in many city streets.
Moderate evidence: One chamber, 5 products, one use each; ozone held at 35–40 ppb (high end for indoors); masked volunteer; no toxicity measured.
Source: Wu 2024, Environmental Science & Technology Letters Link to this fact
Indoor air / Measured in people or real products
Almost everything in a perfume ends up in the air: one perfume released 964 mg of vapor per gram used, mostly alcohol but also about 32 mg per gram of terpene fragrance chemicals.
Moderate evidence: One perfume; emission factors are lower bounds (PTR-MS blind to some compounds).
Source: Wu 2024, Environmental Science & Technology Letters Link to this fact
Indoor air / Journalism
In 2003 Southern California air regulators estimated that household and small-business products, including cleaners, cosmetics, perfume, and room fresheners, released about 108 tons of smog-forming chemicals a day in the Los Angeles region, second only to vehicle tailpipes.
Moderate evidence: Agency inventory relayed by the LA Times; for measured/modeled figures use McDonald 2018 (LA) and Coggon 2021 (NYC 2018: VCPs comparable to vehicle fuels for ozone).
Source: DONTSPRAYCALIFORNIA 2008 (DOJ ADA docket) Link to this fact
Indoor air / Self-reported survey
In a small (n=69) follow-up of Atlanta-area adults with chemical hypersensitivity, the products most commonly reported to trigger symptoms were cleaning agents (88.4%), pesticides (81.2%) and perfume (81.2%), followed by tobacco smoke (82.6%) and car exhaust (72.5%).
Moderate evidence: Small, non-random follow-up sample (n=69, about 35% of the original 199 hypersensitive respondents); self-report of trigger identification, not exposure measurement.
Source: Caress & Steinemann 2003 (EHP), Environmental Health Perspectives Link to this fact
Indoor air / Measured in people or real products
In controlled chamber testing of 12 cosmetic spray products (sunscreens, dry shampoos, hair sprays, a moisturizing and a setting spray, and perfumes) applied 20 cm from the measurement point, one sunscreen spray reached a maximum PM10 particle-number concentration of 1.03 x 10^6 particles per cubic centimeter, and another reached a maximum PM10 mass concentration of 36.17 mg per cubic meter.
Moderate evidence.
Caveats
Single lab, chamber-based, near-field (20 cm) measurement of the immediate spray plume, not a room-average or personal-exposure measurement; one unit tested per product; no replication by an independent group yet.
Source: Dai et al. 2026, ACS Environmental Au Link to this fact
Indoor air / Measured in people or real products
Propellant-based cosmetic sprays (sunscreen, dry shampoo, hair spray) emitted far more submicron particles than pump-based sprays: the two pump perfumes tested stayed below 100 particles per cubic centimeter across all size fractions, while propellant sprays ranged up to hundreds of thousands of particles per cubic centimeter.
Moderate evidence.
Caveats
12 products from unnamed brands, single lab; propellant vs. pump delivery is confounded with product type (perfumes vs. sunscreens/hair sprays), so the difference cannot be attributed to propellant use alone.
Source: Dai et al. 2026, ACS Environmental Au Link to this fact
Indoor air / Other evidence
A lemon-scented general-purpose cleaner, a wood floor cleaner, and a perfume sprayed into a chamber with 95-219 ppb ozone added about 16, 70, and 22 micrograms per cubic meter of fine particles, much less than the air fresheners.
Moderate evidence: Single chamber runs; the floor cleaner run used the highest ozone (219 ppb) so it is not comparable with the others; particle mass modeled from counts.
Source: Sarwar 2004, Journal of the Air & Waste Management Association Link to this fact
Indoor air / Other evidence
In the fragrance industry's 2015 aggregate exposure model, perfume, body spray, and deodorant spray were counted only as skin exposure; the paper reports no figure for how much is breathed in when a spray is used on the body.
Moderate evidence: Industry-funded paper by RIFM, Unilever, P&G, Givaudan and Firmenich staff; it shows the model did not estimate inhalation, not that inhalation is large or small.
Source: Safford et al. 2015, Regulatory Toxicology and Pharmacology Industry-funded Link to this fact
Indoor air / Other evidence
In a lab chamber with a very high ozone level (about 6.5 ppm), all six ordinary perfumes, deodorants and cleaning liquids tested formed new particles; about 0.2% to 17% of the product's evaporated mass became aerosol, with an average near 4%.
Moderate evidence.
Caveats
One lab, six products, a closed 0.68 m3 chamber at roughly 100 times typical indoor ozone, very dry air, no vapor wall-loss correction; a yield, not an indoor concentration. NSF and Sloan funded; no industry funding.
Indoor air / Other evidence
Industry chemists note that indoor air tests for secondhand smoke also pick up cooking, cleaners, furniture polish, perfumes, hair sprays, deodorants and building materials, and one conference-room scan found non-tobacco peaks larger than the tobacco-smoke peaks.
Weak evidence: Industry authors citing an industry report; shows measurement confounding, not that ETS is harmless.
Source: Rodgman & Perfetti 2013 Industry-funded Link to this fact
Indoor air / Other evidence
Personal-use scented products (perfumes, colognes, hair treatments) release their ozone-reactive chemicals close to the breathing zone, so inhaled doses of the reaction products can be larger than room-average models predict.
Weak evidence: A single supporting chamber citation, stated as a qualitative point; no dose given here.
Source: Weschler 2006, Environmental Health Perspectives Link to this fact
Information, not medical advice. See also: myths we won’t tell you.