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5 Skin-Care Ingredients You Should Never Mix—and 4 You Should

Some things go together, like peanut butter and jelly and red wine and aged cheese, but others, especially chemical ingredients, call for stricter pairing suggestions. Here are the dos and don'ts of meshing certain skin care products.

Don’t mix: retinol and hydroxy acids

Since both retinol, aka the topical anti-aging miracle, and hydroxy acids, the anti-wrinkle aid that’s hailed for softening lines, accomplish similar goals of accelerating skin cell turnover, it wouldn’t make total sense to combine them. But, as Joshua Zeichner, MD, the Director of Cosmetic and Clinical Research in Dermatology at Mount Sinai Hospital in New York City, points out, they also both possess potentially irritating side effects—especially when combined. “They’re both harsh on the skin individually, so they cause even more detriment when used together.” Check out the game-changing anti-aging ingredients according to dermatologists.

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Mix: retinol and hyaluronic acid

Most dermatologists are willing to tout the seemingly endless benefits of retinol, which is essentially a form of vitamin A; and nearly all will warn you about its extensive, drying side effects. “Retinol is known to cause irritation to the skin, especially when a proper moisturizing regimen is not put in place,” warns Dr. Zeichner. That’s why a hydrating agent, such as hyaluronic acid, can come in handy. “Retinol is an incredible tool to speed up cellular turnover smooth skin and boosts collagen, while hyaluronic acid helps draw water into the skin providing a plump, glowing complexion,” says Arielle Panarello, medical aesthetician at Union Square Laser Dermatology in New York City. “You can counteract some of the dryness while still letting the retinol penetrate the outer layer of the skin.” Here’s what dermatologists do to look younger overnight.

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Don’t mix: benzoyl peroxide (BPO) and retinol

Whether or not you have sensitive skin, one combo you don’t want to mess with is benzoyl peroxide, a common acne treatment that’s strong enough on its own, and retinol, a clearly potent anti-wrinkle-aiding ingredient. When the two are mixed together, Panarello says that most people experience dry, flaky, and peeling skin. Not the look you’re going for? We don’t blame you. In addition, some research suggests that BPO cancels out the effects of retinol, which totally moots the point of using the often expensive ingredient in the first place.

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Mix: vitamin C and vitamin E

Two vitamins—of course they go together, right? But it’s not that simple. There are a few good reasons why these immune system-fighting and skin-rejuvenating nutrients work hand-in-hand on your skin. “Vitamin C fights against free radical damage and vitamin E is great to boost hydration,” says Panarello. “Used with the powerful antioxidant, ferulic acid, and we have a match made in heaven!” In a nutshell, any old acid, including alpha hydroxy acids (AHAs) and beta hydroxy acids (BHAs), also make a nice combination and work well together to treat uneven pigment, dullness, and acne. “When combining these, you reap antibacterial and anti-inflammatory benefits,” Panarello adds. Don’t forget to include this often missed part of your body in your beauty regimen.

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Don’t mix: vitamin C and hydroxy acids

Most of us consider adding a “vitamin” to our skin-care regimen something similar to topping off our frappuccino with a heaping of whipped cream. Can it really ever hurt? Well, in the instance of vitamin C and hydroxy acid, the answer is, unfortunately, yes. “Vitamin C is a very temperamental ingredient that requires an acidic pH to remain stable and can easily become inactivated,” explains Dr. Zeichner. He recommends not applying it along with retinol, alpha hydroxy acids or beta hydroxy acids, as the formulas likely won’t play well together. Here’s how to get glowing skin naturally.

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Mix: all the alpha hydroxy acids

It may seem counterintuitive that you can mix acids, after all, aren’t they harsh on your skin? Not so. “Low concentrations of several different alpha, or even beta hydroxy acids, may be combined to offer enhanced exfoliation,” explains Dr. Zeichner. “Glycolic and lactic acid are commonly paired with other acids like salicylic acid, malic acid for enhanced exfoliation (especially on the face!).”

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Don’t mix: retin-A and peels or waxing

The skin-care ingredients you apply at morning and nighttime might seem totally different than your once-a-month treatments (i.e. your waxings, peels, or facials), but experts say they impact one another. For example, retin-A and other (weaker) forms of it, such as retinol, are problematic if used alongside peels or waxing procedures. Joel Schlessinger, MD, board-certified dermatologist and RealSelf advisor, always recommends that his patients avoid using them for one day prior to and two days after peels or waxing, when skin may be irritated. “If waxing is done while these are being used, very often small tears in the skin (especially on the eyelids) may occur,” he says. “The same may occur with peels, such as glycolic peels.” Find out the things your waxer secretly wishes she could tell you.

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Mix: benzoyl peroxide (BPO) and salicylic acid

Benzoyl peroxide (BPO) is a topical cure-all for breakouts and blemishes and salicylic acid has also been hailed (for decades!) as a pore-cleanser, pore-minimizer, and total skin exfoliatiant. Together, the two ingredients basically kick butt when it comes to determining the route of your acne problems, says Dr. Zeichner. He suggests trying out a cleanser that incorporates the two, like Aveeno Clear Complexion Foaming Cleanser.

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Don’t mix: certain antibiotics and the sun

You might not think of the sun as a “skin-care ingredient,” but the sun does have serious interactions with a myriad of antibiotics including Tetracycline, Minocycline, Doxycycline, and Bactrim (Sulfa). Additionally, Accutane, a strong form of vitamin A (and parent drug of Retin-A) can be especially likely to cause burns or sun allergies if exposed during treatment, says Dr. Schlessinger. While sunscreens may help to some degree, the damage is often subtle at the time of exposure and severe over time, so caution is the best idea. Find out the sunscreens dermatologists use on themselves.

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Just don’t: overdo it with too many products

Patients can achieve real synergy from using certain products simultaneously, says Tyler Hollmig, MD, director of Laser and Aesthetic Dermatology at Stanford Health Care. “Typically, the key to success is choosing products that act by different mechanisms to achieve a similar goal—for example, using a topical antibiotic to reduce inflammation and kill acne-related bacteria, while also using a retinoid to exfoliate the skin and mature sweat glands is a wonderful and typically safe combination treatment for acne.” From a purely cosmetic standpoint, he suggests using a night moisturizer in combination with a retinoid (tretinoin, adapalene, tazarotene, etc) or azelaic acid-based product (Finacea) to keep your skin smooth and healthy while simultaneously reducing the risk of skin irritation. Now learn how to treat all the different types of acne.