Undecane

Undecane is a volatile hydrocarbon used in cosmetics as a lightweight solvent/emollient (often in small percentages and sometimes as part of C9–C12 alkane blends) and is generally not a classic irritant at typical use levels. However, as a nonpolar solvent it can be mildly defatting and disrupt barrier lipids with repeated exposure, so reactive or eczema-prone skin may experience dryness or stinging, especially in leave-on products or alongside other actives. Given this low-but-nonzero irritation potential in compromised skin, it best fits a “gentle” score rather than inert. Safety Notes: Undecane is most often used as a volatile/light emollient and solvent in leave-on color cosmetics (e.g., long-wear foundations, lip products, sunscreens) where it may appear at low levels (~0.05–1%) as part of a hydrocarbon/solvent blend for slip and dry-down. In high-transfer-resistant, anhydrous or low-water systems (especially long-wear lip color, complexion products, and some spray/serum textures), it can be a primary vehicle alongside other volatile hydrocarbons, reaching the low-to-mid tens; the upper end (~20–25%) reflects consumer-available long-wear formulations where undecane is a major component but not the sole carrier. No specific EU/FDA maximum is set for undecane as a cosmetic ingredient; practical limits are driven by volatility/odor, sensory profile, flammability considerations for aerosols, and compatibility with film formers and waxes.