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.
Health effects / Review of other studies
In the same EPA review, diethyl phthalate (DEP), the phthalate used in fragrance, had only 'slight' evidence of male reproductive effects, the weakest of six phthalates, even though people are exposed to it the most.
Strong evidence: Use to set the record straight, not to accuse fragrance; 'slight' is not 'none' (more high-confidence studies needed).
Source: Radke 2018 (US EPA), Environment International Link to this fact
Health effects / Measured in people or real products
The fragrance-linked phthalate DEP was found in 78% of the hair products tested, and cyclosiloxanes, parabens, and DEP were found at the highest concentrations, including one anti-frizz product that was 38-46% cyclosiloxane by weight.
Moderate evidence: N=18 products; concentration in the product is not the same as absorbed dose or exposure.
Health effects / Review of other studies
In mouse, rat, and zebrafish studies, bisphenol A and phthalates such as DEHP promote weight gain by switching on the master fat-cell gene PPAR-gamma, boosting appetite-driving brain chemicals (neuropeptide Y and AgRP), and triggering low-grade inflammation in fat tissue, often at doses meant to mimic real-world human exposure.
Moderate evidence.
Caveats
These are animal and cell-culture mechanisms; extrapolation to human obesity risk is not established, and effects vary by species, sex, dose, and life stage in ways not yet mapped for humans.
Source: Dalamaga 2024, International Journal of Molecular Sciences Link to this fact
Health effects / Review of other studies
A 2025 systematic review of 18 human studies found bisphenol A, phthalates, and the UV filter octocrylene positively associated with polycystic ovary syndrome (PCOS) in most (though not all) of the studies that tested them.
Moderate evidence.
Caveats
Observational case-control/cross-sectional studies with biomonitoring, not causal evidence; BPA alone had 8-10 positive studies against 2-4 null studies depending on how analogs are counted; most individual chemicals rest on only 1-5 studies.
Health effects / Hypothesis
A 2019 minireview proposes that frequent, long-term burning of scented candles in poorly ventilated rooms may increase bladder cancer risk, based on chemicals in candle emissions (PAHs, benzo[a]pyrene, formaldehyde, phthalates) that are separately linked to bladder cancer via occupational and other non-candle exposure routes.
Weak evidence.
Caveats
No case-control, cohort, or biomonitoring study has ever tested candle use against bladder cancer; the authors' own conclusion calls for that study to be done. This is a narrative minireview with no original data.
Source: Adamowicz 2019, Cancer Prevention Research Link to this fact
Health effects / Review of other studies
Higher urinary MEHHP (a DEHP phthalate metabolite) was correlated with increased urothelial cancer risk in patients with chronic kidney disease; phthalate esters have also been identified in synthetic candle fragrances.
Weak evidence: Single cohort restricted to chronic kidney disease patients, not the general population; not a candle-exposure study; secondhand citation of Huang & Chou 2018.
Source: Adamowicz 2019, Cancer Prevention Research Link to this fact
Information, not medical advice. See also: myths we won’t tell you.