What It Is: One of the most bio-available non-prescription forms of vitamin A products on the market, A+ High-Dose Retinoid Serum is a pro-strength formula for those who want serious results without the unwanted side effects of traditional retinol formulations (reduced appearance of side effects like flaking, redness and irritation compared to high-strength retinol and retinoid products is visible after one use). What It Does: Combining 5% retinoid ester blend, 1% liposomal-encapsulated retinol