Tretinoin is a powerful, first-generation topical retinoid that matches endogenous all-trans-retinoic acid. It functions non-selectively by binding with high affinity to all nuclear retinoic acid receptor subtypes (RAR-α, β, and γ). This binding aggressively accelerates epidermal cell turnover, stimulates mitosis in the basal layers, and thins the stratum corneum. This mechanism forces the extrusion of bound comedones and stimulates dermal fibroblasts to ramp up Type I collagen synthesis. Its structural matrix improves total skin barrier density, reduces hyperpigmentation, and keeps dermal structures systemically protected against UV-induced breakdown.