Isobutane

Isobutane is a volatile hydrocarbon propellant used in aerosol products (often a few to ~30% of the formula) and does not act as a reactive skincare active on the skin. Clinically, it is generally low in irritancy but can cause dryness, transient stinging on compromised/barrier-impaired skin, and irritation via rapid evaporation/cooling or contact dermatitis from the overall aerosol matrix, so it is not truly inert for highly sensitive eczema-prone patients. Safety Notes: Isobutane is used primarily as an aerosol propellant in consumer cosmetics (e.g., hairsprays, deodorant body sprays, dry shampoos, foaming cleansers), where it can appear at very low levels (~0.1–1%) in systems relying mainly on other propellants or reduced-propellant packaging. In high-propellant anhydrous sprays and some foam mousses, total propellant load is often very high, and isobutane can be a major component, reaching roughly 40–70% in the strongest OTC aerosol formats. It is generally not used in conventional non-aerosol leave-on creams/serums, so the meaningful range applies to aerosol/pressurized delivery systems (leave-on sprays and rinse-off foams).