Polyisobutene
Also known as Polyisobutene, PIB, Polyisobutylene
“CIR Expert Panel says: safe as used in cosmetics.”
Polyisobutene is a synthetic hydrocarbon polymer (homopolymer of isobutene) used as a film-former and emollient binder in cosmetics. The CIR Expert Panel conducted a full safety assessment co-covering Polyisobutene and Hydrogenated Polyisobutene (IJT 2008, PMID 19101833): the ingredient is not a dermal irritant, not a sensitizer, not phototoxic, and not carcinogenic in mouse studies. Very limited systemic absorption is expected due to large polymer molecular weight and low water solubility. The 2020 reaffirmation (PMID 32975153) reviewed the polyene group including Polyisobutene and confirmed the original safe conclusion remains in force.
Effective film-forming emollient and binder; used in lip products, mascaras, and skincare at concentrations up to approximately 95% in some lipstick formulations
Not a dermal irritant or sensitizer at cosmetic use concentrations (CIR 2008)
Not phototoxic or photoallergenic — suitable for leave-on sun-exposed formulations
Fully synthetic — no refining-history conditions or PAH contamination risk unlike petrolatum
Not carcinogenic in animal studies; did not promote carcinogenicity of DMBA in mouse studies
- · Non-biodegradable synthetic polymer — environmental persistence concern (not a human safety concern at cosmetic use concentrations)
CIR Quick Reference Table (October 2024) — POLYISOBUTENE row: Finding=S, Citation=IJT 27 (Suppl. 4):83-106, 2008; IJT 39(S2):59-90, 2020
“Polyisobutene S IJT 27 (Suppl. 4):83-106, 2008;IJT 39(S2):59-90,2020”— QRT-Update-100824_0.pdf, p. 249