Huajuhong: Insights into Botany, Phytochemistry, Pharmacology, and Applications in Food, Pharmaceuticals and Beyond

Huajuhong (Exocarpium Citri Grandis, ECG) is derived from Citrus grandis “Tomentosa” or Citrus grandis (L.) Osbeck and has long been used for respiratory health care. Growing interest in natural functional ingredients has drawn increasing attention to ECG as a multifunctional raw material. This review summarizes the botany, ethnopharmacology, phytochemistry, biological activities, and applications of ECG, with particular attention to its amino acid and mineral profiles. A total of 76 flavonoids reported from ECG were compiled. Flavones and flavanones predominated, and naringin was the major constituent. The available in vitro and in vivo studies indicate that ECG and its constituents exhibit antitussive, expectorant, hypoglycemic, hypolipidemic, anti-inflammatory, and antioxidant effects. The underlying mechanisms mainly involve the modulation of smooth-muscle function, the regulation of digestive enzyme activity and lipid-metabolic signaling, maintenance of iron homeostasis, inhibition of inflammatory mediator release, and enhancement of endogenous antioxidant defenses. These properties support its application in teas, functional beverages, lozenges, oral formulations, and other health-oriented products. However, its development is hampered by raw material variability, imperfect quality criteria, limited clinical evidence in humans, and insufficient understanding of ADME and oral bioavailability. Further research on standardized grading systems, constituent–function relationships, and clinical validation is required to support the rational use of ECG.