Evidence is limited to animal or in-vitro work. No human pharmacokinetics. Any human dose in circulation is extrapolated, and extrapolation across species routinely fails.
No pharmacokinetic or half-life data exist. The 2024 CIR assessment reports dermal penetration data demonstrating limited dermal absorption; no systemic pharmacokinetic parameters were established.
Not dosed per administration, used as a percentage in formulation. Per the industry concentration-of-use survey in the CIR assessment: highest maximum reported use is 0.0035% in hair conditioners; highest leave-on maximum is 0.0012% in face and neck preparations and eye lotions. These regulatory-survey concentrations are far lower than the percentages often marketed to consumers.
The CIR Panel concluded these ingredients are safe at present practices of use and concentration, supported by negative human repeated insult patch tests at concentrations higher than maximum reported use, a negative in-vitro dermal irritation study, negative genotoxicity studies, and a negative estrogen agonist assay. The Panel noted changes in the keratin profile of subjects using a facial cream containing it, suggesting a potential biologic effect, but did not consider these adverse. Acknowledged data gaps: no developmental/reproductive toxicity and no carcinogenicity data, judged unnecessary given the low maximum use concentration and limited absorption, a rationale that is concentration-dependent and does not transfer to higher-strength products. Topical only.