👉 Retinoids are a group of naturally occurring compounds that have been used for centuries as natural remedies and cosmetics. They are classified into three main groups based on their chemical structure: 1. Retinoic acid (R-29) group: These are the most common retinoids, including retinol, which is found in vitamin A and some skin care products. 2. Vitamin A (retinyl esters) group: This includes retinol, retinyl palmit