Collagen

Topical collagen (typically hydrolyzed collagen in leave-on products ~0.1–5%) functions mainly as a film-forming humectant/skin-conditioning agent and is generally well tolerated in patch-testing with a low irritancy profile. However, as a protein-derived ingredient it can very occasionally trigger irritation or allergic contact reactions in highly reactive or compromised-skin patients, so it is not truly inert. Given the rare but plausible sensitization risk and my mandate to err on safety for eczema-prone users, it fits “very gentle” rather than “inert.” Safety Notes: In commercial skincare, collagen (typically hydrolyzed collagen/soluble collagen) is often used at low levels (~0.05–0.5%) in leave-on creams/serums and rinse-off cleansers primarily for film-forming and moisturization claims. Many mainstream leave-on products sit around ~1–3%, while the highest consumer-available “collagen” gels/ampoules and masks commonly top out around ~5–10% before viscosity, tack/film feel, odor/color, and stability become limiting. There is no specific FDA/EU maximum limit for cosmetic collagen; practical formulation constraints and sensory performance generally set the upper end.