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The two are often believed to be interchangeable, but the main difference is that retinol is eventually converted into retinoic acid. Retinol is a natural form of vitamin A, while Retin-A is derived from retinoic acid, a synthetic derivative of vitamin A, and considered pharmaceutical.
Not to be confused with Retinal. Retinol, also known as Vitamin A1, is a vitamin found in food and used as a dietary supplement. As a supplement it is used to treat and prevent vitamin A deficiency, especially that which is resulting in xerophthalmia.