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.
Indoor air / Review of other studies
Benzo[a]pyrene levels in fumes from 12 tested scented candles ranged from 0.1 to 7.5 ng/m3, against a WHO guideline value of 1 ng/m3.
Weak evidence: Secondhand citation from this review (Orecchio 2011 not independently read for this evidence base); not this paper's own measurement.
Source: Adamowicz 2019, Cancer Prevention Research Link to this fact
Indoor air / Review of other studies
Measured benzene and naphthalene concentrations emitted by burning candles were reported below the standards considered to exert a toxic biological effect, while sulfur dioxide and benzopyrene concentrations might exceed recommended values in some tested candles.
Weak evidence: Secondhand summary of multiple chamber studies (Derudi, Orecchio) not independently read for this evidence base; heterogeneous across candle brands/types.
Source: Adamowicz 2019, Cancer Prevention Research Link to this fact
Indoor air / Other evidence
Burning scented candles indoors can release formaldehyde, CO2, and volatile organic compounds at levels above indoor background.
Weak evidence: Cites a secondary source (an air-freshener book chapter) not otherwise in this evidence base; not independently checked here against primary chamber measurements.
Source: Nazir et al. 2024, Annals of Medicine & Surgery Link to this fact
Indoor air / Measured in people or real products
Lighting one scented candle for 5 minutes in an ordinary room raised PM10 near the candle (1.52x baseline, 39.9 ug/m3) and kept PM2.5/PM1 elevated for a full hour 3 m and 6 m away (up to 1.97x baseline, ~26-31 ug/m3), with all measured peaks staying below Korea's 24-hour indoor air quality guideline (100 ug/m3 PM10, 50 ug/m3 PM2.5).
Weak evidence.
Caveats
Pilot study of 3 residential houses, one unspecified scented candle burned once for 5 minutes; no replication across candle types, scents, or house configurations, and no chemical (VOC/PAH) measurements.
Source: Yun et al. 2025, Scientific Reports Link to this fact
Indoor air / Measured in people or real products
Finer particles (PM2.5, PM1) from a lit scented candle did not simply decay with distance: their concentration kept rising over the hour measured at 3 m and 6 m from the candle, while PM10 peaked and declined fastest at the candle itself, consistent with warm particle-laden air traveling along the ceiling into adjacent spaces (the Coanda effect).
Weak evidence.
Caveats
Single pilot measurement per location per house (3 houses); mechanism (Coanda effect) is the authors' interpretation, not directly visualized or measured (e.g., no airflow tracer or thermal imaging).
Source: Yun et al. 2025, Scientific Reports Link to this fact
Indoor air / Measured in people or real products
After lighting a scented candle, a nano-sized bacterial extracellular vesicle population (Phyllobacterium myrsinacearum n-ABE) rose from a minor pre-burn component to 23.8-24.0% relative abundance at the candle spot and 6 m away, the first reported detection of this species' extracellular vesicles in indoor air; the authors attribute this to heat/combustion-triggered growth or apoptosis of the existing airborne bacterial population, not a new bacterial source.
Weak evidence.
Caveats
Single pilot study (3 houses), no independent no-candle control run in parallel (before/after design only), no health-outcome or exposure-dose measurement, and the growth-vs-apoptosis mechanism is the authors' proposed interpretation rather than a directly demonstrated causal pathway.
Source: Yun et al. 2025, Scientific Reports Link to this fact
Information, not medical advice. See also: myths we won’t tell you.