Fibronectin

Fibronectin is a large extracellular-matrix glycoprotein used in wound-healing and regenerative skin products at low concentrations to support cell adhesion and repair, and it is not an acid, solvent, or surfactant that commonly causes stinging. Clinical experience and patch-testing data for protein-based bioactives suggest low inherent irritancy for most users, but because it is a biologic protein (often recombinant or human/animal-derived), a small risk of hypersensitivity or irritation exists in highly reactive/eczema-prone skin, so it cannot be scored as inert. Safety Notes: In consumer skincare, fibronectin (typically human/animal-derived or recombinant; often supplied as an aqueous solution and used as part of a growth-factor/ECM complex) is most often present at trace levels in leave-on serums/creams, with effective in-formula levels commonly landing in the ~ppm to tens-of-ppm range. The lowest observed commercial use is around 0.000001% (≈0.01 ppm) when added as a minor component of multi-protein “conditioned media”/growth-factor blends; the highest OTC levels seen are about 0.01% (100 ppm) in niche/high-end regenerative-style leave-on products, with higher amounts being uncommon due to cost, stability, and sourcing/regulatory sensitivities. Rinse-off products rarely include it and, when they do, it is generally at the very low end of this range due to limited deposition and protein denaturation risk.