In Depth Protocol

The Mechanism: Your skin can only utilize pure Retinoic Acid. Any other form of Vitamin A must be converted by your skin's enzymes first, losing significant potency at each step (Kang et al., 1995). Tretinoin: Pure retinoic acid (0 steps). Prescription-only. Highest ROI, but notoriously causes "the purge" (flaking/redness) as the skin adapts. Adapalene (Differin): A synthetic retinoid. Over-the-counter (OTC) in the US. It binds to specific receptors, making it much less irritating than Tretinoin while remaining highly effective for photo-aging and acne (Bagatin et al., 2018). Retinaldehyde (Retinal): 1 conversion step. The best OTC option. It works up to 11x faster than standard retinol with minimal irritation (Saurat et al., 1994). Retinol: 2 conversion steps. The most common OTC option. It works, but it is the slowest to show results. The Application Protocol: Apply your retinoid only at night, as UV light immediately degrades the active ingredient. Wash your face and wait 10-15 minutes until it is completely dry. Applying retinoids to damp skin acts as a penetration enhancer, pulling the acid too deep and causing severe irritation. Use only a pea-sized amount for the entire face. The Morning After: Because retinoids expose fresh, new skin cells, you must apply Vitamin C (as a collagen cofactor) and SPF 50 every morning. Skipping SPF will accelerate UV damage and ruin the protocol.