What it is
Hydrogenated polyisobutene is a synthetic liquid oil made by polymerizing isobutene and then hydrogenating the resulting polymer. It is available in several grades, from lightweight, more volatile versions to heavier ones, and is used in cosmetics as an emollient that leaves skin feeling soft and smooth. Formulators often choose it to replace mineral oil or silicone oils, and it also serves to control viscosity and add shine in products such as lip balms and glosses.
Safety & warnings
Hydrogenated polyisobutene is generally regarded as well tolerated in cosmetic use, with low reported irritation potential and a low tendency to clog pores. As an inert, saturated synthetic oil it is widely used in lip care and leave-on products, including formulas aimed at sensitive skin, though as with any emollient individual responses can vary.
Origin & sourcing
It is fully synthetic. The base polymer, polyisobutene, is prepared by cationic polymerization of isobutene initiated with a strong Brønsted or Lewis acid; this polymer is then hydrogenated to give the stable, saturated liquid oil used in cosmetics.
History
Polyisobutene polymers were developed industrially for uses ranging from plasticizers at low molecular weight to adhesive components at higher molecular weight. The hydrogenated, cosmetic-grade liquid form later became popular in personal care as a clean-feeling alternative to mineral oil and silicones.
Questions everyone asks
Is hydrogenated polyisobutene the same as mineral oil?
No, but it is a synthetic oil often used to replace mineral oil or silicone oils, giving a similar soft, smooth emollient feel.
Will it clog my pores?
Cosmetic references rate it low for comedogenicity, so it is considered unlikely to clog pores for most people.
Why is it in sunscreens?
It works as an emollient and viscosity controller, helping the formula spread smoothly and feel soft on the skin.