Gold

In cosmetics, gold is typically used as colloidal gold, gold flakes, or gold salts at very low concentrations for marketing/optical effects rather than true barrier support. While metallic gold itself is relatively inert, gold compounds are well-documented causes of allergic contact dermatitis in patch testing, and reactions can be significant in eczema-prone or compromised skin. Given the non-essential benefit and credible sensitization/irritation risk in a sensitive-skin population, I score it as moderate. Safety Notes: In mass-market and prestige leave-on skincare (serums, creams, eye gels, sheet masks), gold is typically included at trace/marketing levels (often as colloidal gold or CI 77480) around ~0.0001–0.05%, with some products listing “gold” low in the INCI. High-strength consumer-available products (not prescription/pro-only), especially peel-off masks, luxury creams, and “24K gold” treatments using gold powder/flake or higher-load colloidal dispersions, can reach ~0.1–1.0% total gold-containing material; levels above ~1% are uncommon due to cost, aesthetics (visible particles), and stability/suspension constraints. Rinse-off products generally sit at the lower end because deposition is limited, while leave-on and peel-off formats are where the highest market levels are observed.