Rutin

Rutin is a flavonoid antioxidant/vasoprotective used at low levels (typically ~0.1–1%) to help reduce oxidative stress and visible redness, and it is generally well tolerated in leave-on formulas. Clinical and patch-test experience suggests a low but nonzero risk of irritation or contact sensitivity in highly reactive/eczema-prone patients, often influenced by the solvent system or overall formula rather than rutin itself. Given sensitive-skin safety considerations and the possibility of rare reactions, it fits "very gentle" rather than truly inert. Safety Notes: In commercial skincare, rutin (often listed as Rutin or as part of Sophora japonica flower bud extract standardized for rutin) is frequently used at very low levels (~0.01–0.1%) in leave-on serums/creams for antioxidant and soothing/anti-redness positioning, and sometimes even lower when delivered via botanical extracts. Higher-strength consumer-available brightening/anti-redness concentrates and “bioflavonoid” antioxidant serums can reach ~1–5% rutin, with the upper end constrained mainly by solubility/stability and sensory effects rather than explicit regulatory limits (no specific EU/FDA maximum for rutin as a cosmetic ingredient). Rinse-off products (cleansers) tend to sit toward the low end due to short contact time and cost-to-benefit considerations.