Polybutene

Polybutene is a high–molecular weight synthetic hydrocarbon used as an emollient/occlusive (often a few to ~20%+) in lip products and creams, and it is generally non-reactive and not pH-dependent. Clinical experience and patch-test data indicate a very low rate of irritation or sensitization, with reactions being uncommon and usually limited to rare individual intolerance or occlusion-related discomfort. Given its broad tolerability even in sensitive populations but acknowledging that virtually any leave-on occlusive can bother a small subset of highly reactive or eczema-prone patients, it best fits an exceptionally gentle (not truly inert) score. Safety Notes: In commercial skincare and lip products, polybutene is commonly used at low levels (~0.1–3%) as a slip agent/binder in creams, lotions, sunscreens, and cleansers (both leave-on and rinse-off). The highest consumer-available uses are in anhydrous, high-gloss occlusive formats—especially lip glosses, lip oils, and balms—where polybutene can serve as a primary base fluid and reach ~20–60% depending on viscosity grade and the presence of other oils/hydrogenated polyisobutene. There are no specific EU/FDA cosmetic concentration limits for polybutene; practical limits are driven by sensorial goals, clarity, and viscosity/stability of the anhydrous system.