Category: biosynthesis
Skin barrier renewal: basal keratinocytes proliferate, differentiate upward through stratum spinosum + granulosum, mature into anucleate corneocytes of stratum corneum, shed (~28-day turnover). Hyperkeratosis (acne, psoriasis, ichthyosis) reflects dysregulated terminal differentiation. AHAs/BHAs accelerate corneocyte shedding (chemical exfoliation): AHAs (glycolic, lactic, mandelic) — water-soluble, surface; BHAs (salicylic) — lipid-soluble, penetrate sebaceous follicles. Melanogenesis in melanocytes: tyrosinase oxidizes tyrosine → DOPA → dopaquinone → eumelanin (brown/black, MC1R-driven) or pheomelanin (red/yellow). Hyperpigmentation Rx blocks tyrosinase (hydroquinone, kojic acid, arbutin) or inhibits melanin transfer (azelaic acid, niacinamide) or downregulates MITF/PAR-2 (tranexamic acid topical, bakuchiol).