Castanea Crenata Shell Extract

Castanea crenata (Japanese chestnut) shell extract is typically used at low concentrations as an antioxidant/astringent, often rich in polyphenols and tannins. While generally tolerated in many users, tannin-heavy botanical extracts can provoke stinging, dryness, or flare reactions in eczema-prone or barrier-compromised skin, and botanical extracts carry some risk of delayed sensitization. Given the limited standardized clinical irritation data and the known reactivity of astringent botanicals in sensitive populations, a mild (0.4) irritancy score is the safest clinically aligned assessment. Safety Notes: In commercial skincare, Castanea crenata (Japanese chestnut) shell extract is most often used as a minor botanical active in leave-on toners/serums/creams, where it commonly appears at trace-to-low levels around 0.001–0.1% as part of multi-extract blends. Higher-strength consumer products (typically brightening/antioxidant or “pore/texture” serums and ampoules, and some wash-off masks) can push the neat extract to ~0.5–3% depending on extract carrier/standardization and color/odor constraints. No specific global cosmetic maximum is established for this INCI; practical upper limits are mainly driven by sensory impact, solubility/compatibility, and stability rather than regulation.