Polygonum Cuspidatum Root Extract

Polygonum cuspidatum (Japanese knotweed) root extract is primarily used as an antioxidant/soothing botanical source of resveratrol and related polyphenols, typically at low percentages in leave-on products. While generally tolerated, botanical extracts have documented variability in composition and can trigger irritant or allergic contact dermatitis in reactive and eczematous skin, especially when used repeatedly or layered with other actives. Given the non-essential nature of the extract and the real-world sensitization risk in sensitive populations, a mild (0.4) score is the safest clinically aligned assessment. Safety Notes: In mass-market leave-on serums/creams and K-beauty-style antioxidant blends, Polygonum Cuspidatum Root Extract is commonly used as a minor botanical component around 0.01–0.1%, often alongside other plant extracts and/or as a supporting source of resveratrol. Higher-strength consumer products (primarily leave-on serums and targeted brightening/antioxidant treatments) use the extract at ~1–5% when it is a highlighted active, with the practical upper end driven by odor/color, solubility/clarity, and stability constraints; rinse-off products generally sit toward the low end due to cost and short contact time.