Mix: Retinol and Glycerin
Retinol is a miracle skin-care ingredient, but it's also pretty drying. That's why dermatologists and estheticians urge their patients and clients to use it sparingly. It's also recommended to use a bit at a time until skin is accustomed to it and stops peeling from it. One ingredient that can help prevent irritation when using a retinol-containing product is glycerin, a powerful humectant that helps draw water to the skin.
"When used together, they work synergistically to combat the signs of aging while also moisturizing the skin to minimize the irritating effects of retinoids," Dr. Imahiyerobo-Ip says. A great product that combines the amazing benefits of a retinol with the moisturizing benefits of glycerin is Hydropeptide's Nimni Cream ($224).
Don't Mix: Vitamin C and Alpha Hydroxy Acids
Both of these ingredients offer antioxidant benefits, but when combined, they can throw off the pH balance of your skin due to too high levels of acidity. Products containing vitamin C as an ingredient contain low levels of acidity (typically a three on a scale of 14). When you use this kind of product along with an alpha hydroxy acid, like glycolic or lactic acid, you're essentially reducing the effectiveness of the vitamin C product. Is it dangerous or irritating to combine them? Probably not. But you'll be wasting a whole lot of what might be an expensive product if you do.
Don't Mix: Niacinamide and Alpha Hydroxy Acids
Also known as vitamin B3, niacinamide is a skin conditioning agent that helps repair and refine the skin's structure. It tends to work best in an environment with a neutral pH, which we just explained is certainly not alpha hydroxy acids, as they have an extremely low pH level.
"When used in a product containing high levels of alpha hydroxy acids (i.e., glycolic or lactic), nicotinic acid is produced, which may result in skin flushing and potential irritation," Ramya Viswanathan, product development manager at Biossance, says. While it won't necessarily harm you to use them both together, they basically cancel each other out.
