The rapid growth of the global population has led to significant environmental impacts, driven by the unsustainable extraction of resources and waste generation. To address these challenges, the valorisation of by-products from different industries is crucial for maximising resource efficiency, reducing waste, and promoting sustainable practices. In this study, a comprehensive characterisation of the physicochemical properties of plant-based by-products, including rice husk (RH), oregano stalks (OS), eucalyptus leaves (EL), and almond shells (AS), was conducted. The analyses of the residues showed that, despite the similarities regarding cellulose and lignin content in all materials, RH and OS present a higher cellulose content, while EL and AS contain a greater percentage of oils. Additionally, calcium and potassium were identified as the metals at higher concentrations in all residues. The EL and RH present significant hydrophobic properties compared to the other analysed residues, showcased by their lower wettability. The morphological analyses of the waste residues revealed that OS and RH particles exhibit fibrous characteristics with heterogeneous sizes, while EL is a blend of fibrous and amorphous particles, and AS is composed of smaller particles with irregular shapes. All the residues retained their antioxidant properties over a 12-month storage period, with no degradation due to grinding. The composition and physicochemical properties of these residues highlight their potential to be used in distinct industries, including construction, transport, and textiles, promoting a circular economy and supporting a more sustainable environment.

Background/Objectives: Skin dysbiosis is associated with several dermatological disorders and is often accompanied by oxidative stress and inflammation. Bioactive textiles offer a promising strategy for localized skin health management; however, many currently available materials rely on synthetic or metal-based agents. This study aimed to develop sustainable cotton-based bioactive textiles functionalized with acorn shell (AS) extract, an agri-food by-product rich in phenolic compounds, and evaluate their biological performance potential for skin-contact applications in the management of skin dysbiosis conditions. Methods: Cotton fabrics were pre-treated with chitosan, a commercial cationic agent, or potassium alum and functionalized with AS extract using exhaustion or padding techniques. The resulting materials were assessed for antimicrobial activity against skin-associated bacteria, antioxidant capacity, anti-inflammatory activity in LPS-stimulated macrophages, cytocompatibility with keratinocytes and macrophages, and phenolic compound release under skin-mimicking conditions. Results: AS-functionalized cotton exhibited strong antimicrobial activity, particularly against Gram-positive bacteria, together with significant antioxidant and anti-inflammatory effects. All functionalized textiles maintained keratinocyte viability above established cytocompatibility thresholds, supporting their suitability for direct skin contact. Exhaustion-treated samples showed higher phenolic incorporation and release, resulting in enhanced biological performance, whereas padding-treated fabrics exhibited lower phenolic loading, more sustained release profiles, and comparatively reduced bioactivity. Conclusions: AS extract can be successfully incorporated into cotton textiles using industrially relevant finishing methods, generating multifunctional materials with antimicrobial, antioxidant, and anti-inflammatory properties while maintaining cytocompatibility. These findings support the potential of AS-functionalized cotton as a sustainable, plant-based skin-contact textile platform for localized management of skin-dysbiosis-associated conditions, with great relevance for dermatological and healthcare applications.