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