B-Silk Protein Firm + Replenish Serum

These describe what an ingredient is, not whether it is a problem. The stance marks above are the ratings; these are not.

• humectantSodium PCA

  • Sodium PCA: The salt of PCA, one of the water-holding substances the outer layer of skin makes for itself. Dörner C, Steinbinder J, Sachslehner AP, Sukseree S, Eckhart L, "Amino Acid Metabolism of the Skin: Control by Specific Enzymes and Contribution to Protective Functions", Metabolites 2025;15(9):601, DOI 10.3390/metabo15090601, open access, section "Glutamine Is Converted to Pyrrolidone Carboxylic Acid, a Component of the NMF": "pyrrolidone carboxylic acid (PCA), also known as pyroglutamic acid or 5-oxoproline, accumulates in the stratum corneum."

• barrier lipidCeramide AP, Cholesterol

  • Ceramide AP: One of the lipid families the skin barrier is actually built from. Feingold KR and Elias PM, "The role of ceramides in the disruption of the cutaneous permeability barrier, a common manifestation of skin disorders", J Lipid Res 2024;65(8):100593, DOI 10.1016/j.jlr.2024.100593, open access: the barrier lipid matrix "by weight is approximately 50% ceramides, 25% cholesterol, and 15% free fatty acids".
  • Cholesterol: One of the three lipid classes that make up the skin barrier, alongside ceramides and fatty acids. Feingold KR and Elias PM, J Lipid Res 2024, open access: the barrier lipid matrix "by weight is approximately 50% ceramides, 25% cholesterol, and 15% free fatty acids". Corroborated by Wertz PW, "Roles of Lipids in the Permeability Barriers of Skin and Oral Mucosa", Int J Mol Sci 2021;22(10):5229, DOI 10.3390/ijms22105229, PMID 34063352.