The full read
Long recommended "on instinct" by dermatologists, the sandwich technique (moisturizer before and/or after retinol) has just been tested directly: an ex vivo study presented at AAD 2025 measured actual retinol/tretinoin bioactivity depending on how it's layered. The result: an "open sandwich" (moisturizer before OR after, not both) preserves retinoid bioactivity; a "full sandwich" (moisturizer-retinol-moisturizer) reduces it roughly threefold, through dilution and a stronger penetration barrier — which is actually useful for beginners easing into a retinoid. A separate randomized trial in patients on oral or topical retinoids found that applying a plain moisturizer twice daily significantly reduced dryness and flaking, with no reported loss of efficacy. The specific product in the video (a centella/panthenol balm) wasn't tested itself in these studies, but the principle it illustrates — using a rich moisturizer to soothe retinol irritation — is now backed by mechanistic data, not just informal clinical experience.
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