Natural remedies for post-inflammatory hyperpigmentation: Antibacterial and anti-melanogenesis properties of Thai herbs

Abstract

Post-inflammatory hyperpigmentation (PIH) occurs when excess melanin is produced in response to skin irritation or injury, resulting in uneven pigmentation. This study evaluates the cosmeceutical potential of ethanolic extracts from eight Thai herbs—Curcuma xanthorrhiza (CX), Quercus infectoria (QI), Calophyllum inophyllum (CI), Caesalpinia sappan(CS), Garcinia hanburyi (GH), Punica granatum (PG), Cotylelobium lanceolatum (CL), and Strychnos nux-vomica (SN)—to treat PIH through antioxidant, anti-inflammatory, antibacterial, and anti-melanogenesis properties. Phytochemical analysis revealed that CX and QI contained high levels of phenolics and flavonoids, correlating with their strong antioxidant activity. CX also protected against hydrogen peroxide (H₂O₂)-induced oxidative stress in a yeast-based model and prevented DNA damage in vitro, helping to mitigate cellular injury that can lead to melanin overproduction. Anti-inflammatory assays showed that both CX and QI significantly reduced nitric oxide and interleukin-6 (IL-6) levels without causing cytotoxicity, supporting their role in treating inflammation-related PIH. The extracts also demonstrated selective antibacterial activity against Staphylococcus aureus (MSSA and MRSA) and Cutibacterium acnes, while sparing Staphylococcus epidermidis, an important member of the skin microbiome. CI and CX significantly inhibited C. acnes, a key contributor to acne-induced PIH. Finally, anti-melanogenesis assays revealed that QI and SN effectively inhibited α-MSH-induced melanin production. These findings suggest that CX, QI, and CI are promising natural cosmeceutical agents for addressing PIH by modulating oxidative stress, inflammation, microbial imbalance, and melanin overproduction, while maintaining skin microbiota integrity.