Squalene

Squalene is a skin-identical emollient/lipid typically used around 0.5–10% to reduce transepidermal water loss and improve barrier feel, and it is generally well-tolerated in sensitive and eczema-prone populations. Human repeat-insult patch testing and clinical use data show low irritation and low sensitization rates, with reactions being uncommon and more often related to impurities/oxidation rather than the molecule itself. Because rare irritation or comedogenic flares can still occur in highly reactive individuals, it is not fully inert, but it remains very gentle at typical cosmetic concentrations. Safety Notes: In commercial skincare, squalene is often used at very low levels (~0.05–0.5%) as part of the emollient/oil phase in cleansers, lotions, and creams where it contributes slip and barrier support without greasiness. Typical leave-on facial moisturizers and serums commonly fall around ~1–10%, while high-emollience balms/oils and “100% squalene” single-ingredient facial oils sold OTC reach the practical maximum of 100%. There is no specific EU/FDA cosmetic maximum for squalene; the main constraints are oxidation/stability and sensory profile, with leave-on products spanning the widest range.