In the context of chronic exposure to atmospheric pollutants, sericin acts as a bioactive protein matrix capable of organizing itself on the skin surface into a continuous molecular film endowed with selective barrier properties. Its high density of polar groups — particularly serine, aspartic acid, and glycine residues — enables the formation of a three-dimensional network stabilized by hydrogen bonds and electrostatic interactions that, in terms of rheological behavior and water-retention capacity, mimics the corneodesmosomal fraction of the stratum corneum.
This structure gives sericin a dual function: reducing the deposition of fine particulate matter on the skin surface and limiting its diffusion through intercorneocytic microchannels. The protein film acts as a bioadhesive interface with controlled permeability, showing a semi-occlusive behavior that does not compromise physiological TEWL while hindering the penetration of particles with an aerodynamic diameter below 2.5 µm, which represent the most reactive fraction of urban particulate matter.
Interaction with fine particulate matter and modulation of surface charge
PM2.5 has a chemically active surface characterized by transition metals, polycyclic aromatic hydrocarbons, and oxidizing compounds. Thanks to the presence of negatively and positively charged domains distributed along its polypeptide chain, sericin exhibits an amphoteric behavior that allows electrostatic interactions and selective adsorption phenomena. The result is the formation of protein–particulate complexes with low surface mobility. This process reduces the ability of the particles to interact directly with the lipids of the stratum corneum and with keratinocyte cellular receptors, decreasing the activation of inflammatory pathways mediated by AhR (aryl hydrocarbon receptor) and NF-κB, which are typically induced by atmospheric pollutants.
At the same time, the modulation of the skin surface charge induced by the sericin film alters particulate adhesion dynamics, reducing van der Waals forces and hydrophobic interaction with the oxidizable squalene of sebum.
Scavenger effect against reactive oxygen species
One of the most evident aspects in anti-pollution protection is the ability of this silk protein to act as a redox buffering system. Amino acid residues containing hydroxyl and carboxyl groups function as electron donors, neutralizing ROS generated both directly by particulate matter and secondarily by mitochondrial activation in keratinocytes. This behavior results in a reduction of lipid peroxidation in the stratum corneum, with particular reference to the protection of polyunsaturated fatty acids in ceramides and squalene. The preservation of lipid integrity maintains intercorneocytic lamellar cohesion and limits the permeability increase induced by urban oxidative stress.
Stabilization of the skin microbiome in polluted environments
The urban environment profoundly alters the microbial ecosystem of the skin surface, promoting pro-inflammatory strains and reducing biodiversity. Sericin creates a hydrated microenvironment with low pH fluctuation that supports the growth of beneficial commensals and hinders the adhesion of opportunistic microorganisms. Its protein structure also acts as a bioselective substrate for the adsorption of bacterial toxins and heavy metals, reducing their bioavailability and their interaction with keratinocyte toll-like receptors. Exposure to PM2.5 and ozone leads to increased expression of IL-1α, IL-6, and TNF-α at the epidermal level. By reducing oxidative stress and limiting the direct contact between pollutants and cell membranes, sericin modulates the upstream activation of inflammatory cascades.
It has been observed that the protein microfilm reduces MAP kinase phosphorylation and the nuclear translocation of NF-κB, with a consequent decrease in the production of pro-inflammatory mediators and metalloproteinases responsible for dermal collagen degradation.
Synergy with the barrier function of the stratum corneum
From a biophysical standpoint, sericin increases the water-retention capacity of the stratum corneum through the formation of a hygroscopic network that traps water molecules. This effect improves corneocyte plasticity and reduces the formation of microfissures through which particulate matter could penetrate. The protein also acts as a temporary scaffold for the reorganization of intercorneocytic lipids, promoting a more compact lamellar arrangement that is more resistant to chemical aggression. Its use in topical anti-pollution systems is increasingly oriented toward low molecular weight forms and nanostructured complexes capable of improving bioadhesion and wash-off resistance. Physical cross-linking technologies allow the creation of smart films responsive to pH and environmental humidity, with a modulated release of antioxidant actives.
In this context, sericin is not merely a film-forming agent but a multifunctional biomimetic platform capable of integrating physical protection, redox modulation, and support of the barrier function under conditions of chronic urban stress.
