Azelaic AcidvsZinc Oxide

Azelaic acid exhibits multi-modal activity: (1) Tyrosinase inhibition—competitively inhibits tyrosinase selectively in hyperactive melanocytes (melasma, PIH) while sparing normal ones; may involve mitochondrial enzyme interference in dysregulated melanocytes. (2) Antimicrobial—bacteriostatic against Cutibacterium acnes by inhibiting bacterial protein synthesis. (3) Comedolytic—normalizes follicular keratinization, reducing hyperkeratinization and corneocyte cohesion; may modulate keratinocyte differentiation. (4) Anti-inflammatory—scavenges ROS, inhibits neutrophil free radicals, reduces pro-inflammatory cytokines. Inhibits 5-alpha-reductase in sebocytes, potentially reducing sebum. Multi-pathway activity explains efficacy in acne, rosacea, and hyperpigmentation. Safe during pregnancy.

Zinc oxide particles sit on the skin surface and primarily scatter and reflect UV radiation across the full UVA (320–400 nm) and UVB (280–320 nm) spectrum via Rayleigh and Mie scattering. At nano scale, zinc oxide also absorbs UV photons and undergoes semiconductor band-gap excitation, converting UV energy to heat—a mechanism similar to organic chemical filters. It provides the broadest single-ingredient UV coverage available. Beyond photoprotection, zinc oxide exerts anti-inflammatory effects by inhibiting NF-κB activation, reducing pro-inflammatory cytokine release (TNF-α, IL-6), and modulating Toll-like receptor signaling. It supports barrier repair by promoting occludin and zonula occludens-1 expression in tight junctions. Zinc ions have mild antimicrobial activity against Staphylococcus aureus and Candida species. These properties underlie its use in diaper rash creams, wound care, and post-procedure skincare. Zinc oxide does not penetrate intact stratum corneum when formulated as micronized or nano particles.