Vitamin A (OTC) / All-Trans Retinol
The most evidence-backed OTC anti-aging ingredient. Converts in skin to retinaldehyde then retinoic acid, which binds nuclear RAR receptors to regulate gene expression: driving cell turnover, collagen I and III synthesis, MMP downregulation, and acne normalisation. Decades of controlled trials confirm efficacy for wrinkles, texture, pigmentation and acne.
PM only, 0.025–1%. Start 1–2x per week for 4 weeks, build frequency slowly. Sandwich technique (moisturiser → retinol → moisturiser) reduces irritation. Avoid during pregnancy.
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