Don’t Mix: Retinol and Vitamin C Retinols and retinoids are powerful ingredients that address several skin-care concerns, from diminishing fine lines and wrinkles and preventing acne to lightening brown spots and increasing collagen production. This is why you’ll find a retinol-based product in many dermatologists’ skin-care routines. “The main concern with retinol-based products is skin irritation,” Dr. Imahiyerobo-Ip says. “There are several active ingredients that may increase the chance of irritation with retinoids, one being vitamin C.” Like retinol, vitamin C (L-ascorbic acid) is effective in combating the signs of aging, including fine lines, firmness, and uneven skin tone. However, when these products are used together, they may cause irritation…