Hydrogenated Polyisobutene

Hydrogenated polyisobutene is a saturated, inert emollient/occlusive (often 1–30%+) used to reduce transepidermal water loss and improve slip, and it is generally non-reactive with a very low rate of irritation in patch testing and clinical use. It is non-volatile, non-acidic, and not a known sensitizer, making it suitable for compromised barriers, though rare individual intolerance or acne/follicular issues can occur. For severe sensitivity and post-procedure skin, I score it as exceptionally gentle rather than completely inert because real-world formulations and individual variability can still produce occasional reactivity. Safety Notes: Hydrogenated polyisobutene is used as an emollient/occlusive and slip agent; in many leave-on lotions, serums, and sunscreens it appears at low supporting levels around 0.1–2% to improve sensory feel and reduce tack. In richer creams, makeup, and hair/skin oils it commonly sits in the ~3–30% range, while in consumer lip oils/glosses, balm sticks, and anhydrous occlusive concentrates it can serve as a primary base oil and reach very high levels (50–90%). It is rarely used at high levels in rinse-off cleansers due to wash-off format and surfactant structure, but there are no specific EU/FDA concentration caps for this ingredient in cosmetics, so maximum levels are primarily determined by aesthetics and viscosity.