A functional food approach: probiotic-fermented Angelica spp. improves skin hyperpigmentation via gut-skin axis and its microbial metabolite hippuric acid

Background Angelica dahurica (Bai-zhi) and A. sinensis (Dang-gui) are traditional food-medicines used for skin disorders, but the mechanism of their oral efficacy remains unclear. Probiotic fermentation is a promising strategy to enhance the bioactivity of plant-based foods. Objective This study aimed to investigate the functional nutritional properties of probiotic-fermented Angelica spp., evaluate its anti-melanogenic efficacy, and elucidate the role of gut microbiota remodeling and the microbial metabolite hippuric acid (HA) in mediating these effects via the gut-skin axis. Methods The aqueous extract of A. dahurica and A. sinensis was fermented with L. plantarum . The fermented broth (FB) was chemically profiled and assessed for antioxidant and anti-melanogenic activity in B16F10 cells. Its efficacy was evaluated in a UVB/progesterone-induced hyperpigmentation mouse model treated with FB orally (GI) or topically (EI). Gut microbiota (16S rRNA sequencing) and metabolomic profiles were analyzed. The role of the key metabolite, hippuric acid (HA), was further investigated in vitro using HT-29 cells. Results Fermentation enriched bioactive constituents such as salicylic acid and vitamin B2. FB exerted direct anti-melanogenic effects in vitro and exhibited notable in vitro antioxidant activity. In vivo , it relieved UVB/progesterone-induced hyperpigmentation primarily by remodeling gut microbiota and boosting circulating HA. HA modulates transcription of intestinal immune-related genes including NR1H4 and IL-1β, and its concentration positively correlated with beneficial gut taxa. This metabolite alleviates systemic inflammatory signals that promote melanin overproduction via regulating intestinal immune programs. Conclusion Our findings reveal that probiotic fermentation transforms traditional food-grade Angelica spp. into a potent functional food. Its skin-beneficial effect is mediated by the gut microbiota-derived metabolite HA, highlighting a novel mechanism by which dietary phytochemicals can improve skin health via the gut-skin axis and offering a scientific basis for the modern application of traditional foods.