## 7 Conclusions, Limitations, and Future Perspectives
Nevertheless, a proof of concept for a possible application to valorize extracts from kiwi by-products, applying the principles of sustainability and the circular economy to the food and cosmetics industries, is needed. Despite promising results, other studies are needed to evaluate safety and other properties. Thus, safety issues and other limitations, including in regard to sustainability, also exist and need to be considered for such applications. For example, while kiwi fruit offers numerous health benefits due to its rich bioactive content, several limitations must be considered when incorporating kiwi bioactives into functional products. The primary limitation is its allergenic potential, as kiwi fruit can cause allergic reactions, ranging from mild oral allergy syndrome (OAS) to severe anaphylaxis, restricting its use in functional foods for the general population. Additionally, kiwi bioactives, such as vitamins, antioxidants, and enzymes, can degrade during processing and storage, affecting the efficacy and nutritional value of functional products, making it challenging to ensure these compounds remain stable and bioavailable. Furthermore, kiwi fruit allergens can cross-react with other common allergens like latex and birch pollen, necessitating clear labeling of functional products to inform consumers of the potential risks. In regions with a high incidence of these related allergies, the use of kiwi bioactives may need to be limited to avoid adverse reactions among sensitive populations. Addressing these limitations requires innovative approaches in food technology and allergen management to safely and effectively incorporate the health benefits of kiwi bioactives into functional products. Diagnosis relies on skin prick tests (SPTs), specific IgE tests, and the prick-by-prick method, using fresh fruit for higher sensitivity. Component-resolved diagnostics (CRDs) aid in identifying allergens like Actinidin (Act d 1), associated with severe reactions, even in non-pollen allergic individuals. Thaumatin-like protein (Act d 2) contributes to cross-reactivity with mold allergens. Regional differences exist in symptom presentation, with systemic reactions more frequent in central and southern Europe, contrasting with milder oral symptoms in central/western Europe. Children often exhibit mono-sensitization to kiwi fruit, while adults commonly display multiple sensitizations, reflecting demographic variability in allergy patterns [124]. Some allergic reactions to kiwi fruit have been reported, but the mechanisms behind the reaction are still unclear. Nevertheless, very scarce information is available in the literature about this topic. Thus, more research is necessary on the toxicity of kiwi bioactives and extracts to ensure consumer safety when they are added to a new product. For example, cytotoxicitystudies of extracts must be performed to confirm their security for human applications. The stability of cosmetic formulations should be analyzed for longer periods, ideally six months, and their moisturizing properties must also be assessed. Finally, a sustainability assessment should also be performed prior to such an application, to analyze factors such as the carbon footprint, resource consumption, and end-of-life disposal, to clearly understand the impact of the production of novel functional foods and cosmetic products, in comparison to commercial ones. Conceptualization, A.T.; methodology, A.T.; software, A.M.M., K.C., S.I.K., M.A.F., A.O. and A.T.; validation, A.T.; investigation, A.M.M., K.C., S.I.K., M.A.F., A.O. and A.T.; writing--original draft preparation, A.M.M., K.C., S.I.K., M.A.F., A.O. and A.T.; writing--review and editing, A.T.; visualization, A.T.; supervision, A.T.; project administration, A.T. All authors have read and agreed to the published version of the manuscript. This research received no external funding. The authors would like to thank the School of Chemistry of the Faculty of Science at the Democitus University of Thrace for its continuous support.