Skin-Care Ingredients You Should Never Mix, and Ones You Can

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 in those with sensitive skin.

Mix: Retinol and Hyaluronic Acid

Hyaluronic acid is another powerful humectant that can hold up to 1,000 times its weight in water, meaning it does wonders in hydrating the skin. “Skin loses water and moisture as we age, and especially with the use of drying ingredients such as retinol in other products,” Dendy Engelman, MD, a dermatologist in New York City, says. “This ingredient will help store hydration.”

Her go-to to use in combination with a retinol-containing product is SkinMedica HA5 Rejuvenating Hydrator ($184), which is a hydrator with a gel-like consistency that contains five different types of hyaluronic acids.

Don’t Mix: Retinol and Salicylic Acid

If you find yourself tempted to combine retinol and salicylic acid, two powerhouses for fighting signs of aging, think again. Combining salicylic acid and tretinoin, for example, is risky. “Retinol is extremely unstable,” NYC-based dermatologist, Joshua Zeichner, MD, FAAD, previously told PS. “It doesn’t play nicely with a salicylic acid or benzoyl peroxide. Combining two leave-ons, like masks or overnight treatments, can hit the skin too hard if you use them all at one time.”

Don’t Mix: Retinol and Glycolic Acid

Glycolic acid is a chemical exfoliant in the alpha-hydroxy acids (AHAs) family that helps improve the skin’s texture, minimize pore size, and also helps with brown spots. Glycolic acid, as well as lactic acids and salicylic acids, are often found in face washes in low concentrations.

“While these products can be used with retinol-based products, you do not want to use these products one right after the other, particularly if you have sensitive skin,” Dr. Imahiyerobo-Ip says. If you must use acid washes, she suggested using them in the morning and using your retinol-based products at night followed by a gentle moisturizer.

Don’t Mix: Benzoyl Peroxide and Salicylic Acid

Benzoyl peroxide and salicylic acid are both great ingredients for treating acne. In some cases, using them together in a formulation can make them more effective at banishing breakouts. That said, most experts don’t recommend mixing two different products with these ingredients together. This is because in the wrong dosage, the two powerful ingredients can cause skin irritation.

Don’t Mix: Salicylic Acid and Vitamin C

Salicylic acid and vitamin C are two very different ingredients and when used together in the right way, can really help you accomplish the bright, clear skin of your dreams. That said, you shouldn’t use them at the same time. It’s best to use vitamin C in the morning and salicylic acid at night to avoid irritation.

Don’t Mix: Benzoyl Peroxide and Retinol (Such as Adapalene or Tretinoin)

If you’ve been dealing with acne for a while, you probably already know that both of these ingredients work to prevent breakouts, and you may find yourself wondering, Can you use benzoyl peroxide with retinol? But there’s a good reason benzoyl peroxide and adapalene are not often used in combination in the very same product. “Benzoyl peroxide is a potent acne product that’s great for inflammatory acne, but many people are unaware that benzoyl peroxide can inactivate a topical retinol,” Dr. Imahiyerobo-Ip says.

This doesn’t mean that you cannot use benzoyl peroxide during the same period that you’re using retinol; it just means benzoyl peroxide and tretinoin should never be layered on top of each other or you’ll be in for a rude (and red) awakening. Dr. Imahiyerobo-Ip recommends using benzoyl peroxide in the morning and a retinoid at night.