Emerging therapeutic and cosmeceutical applications of phenylalanine and its metabolites

OBJECTIVE: This review aims to comprehensively examine and integrate the extant knowledge pertaining to phenylalanine (Phe) and its key metabolites, namely tyrosine (Tyr), phenylpyruvic acid (PPA), phenyllactic acid (PLA), and phenylacetic acid (PAA). The primary focus of this review will be on the emerging pharmacological and cosmetic applications of these metabolites. RATIONALE: Phe-derived compounds have garnered increasing attention due to their diverse pharmacological effects, including antioxidant, antimicrobial, anti-inflammatory, and neuromodulatory properties. Their relevance to skin health, pigmentation regulation, microbiome modulation, and mood-related dermatoses provides a compelling basis for reviewing their functional potential in both therapeutic and cosmetic contexts. METHODS: A systematic literature review was conducted using PubMed, Web of Science, and Scopus up to 2025. The review was guided by predefined keywords related to Phe and its metabolites. The inclusion criteria were tailored to encompass experimental, clinical, and translational studies that explore pharmacological or cosmetic applications of Phe. MAIN FINDINGS: The review presents compelling evidence substantiating the bioactivity of Phe and its metabolites across multiple skin-related pathways. These compounds exhibit promising efficacy in preserving skin homeostasis, regulating pigmentation, harmonizing cutaneous microbiota, and mitigating psychosomatic skin conditions. Their structural and functional diversity renders them versatile agents with extensive translational potential. CONCLUSIONS AND IMPLICATIONS: The multifunctional nature of Phe-derived compounds presents substantial potential for incorporation into advanced skincare and pharmaceutical formulations. However, limitations persist in safety and toxicological data, particularly concerning prolonged human exposure. Future research should prioritize (i) mechanistic elucidation of biological effects, (ii) standardized toxicological and clinical validation, and (iii) formulation optimization to facilitate safe and effective applications. These endeavors have the potential to bridge the gap between biochemical research and practical innovation, thereby fostering novel solutions for skin health and emotional well-being.