The Skin-Care Ingredients You Shouldn’t Mix

Vitamin C, retinol, salicylic acid, glycolic acid, peptides — the list of buzzy skin-care ingredients goes on and on. With so many new product formulations and ingredient advancements popping up left and right, it can be hard to keep track of what can and cannot be used together. To give you a lesson in skin-care ingredients 101, we spoke with board-certified dermatologist and Skincare.com consultant Dr. Dendy Engelman.

When skin-care ingredients are working against each other, it can present itself in an array of ways. “If the skin is irritated, red, sensitive, dry or the targeted skin issue is not improving,” Dr. Engelman explains, these could all be signs the active ingredients in the products are competing with each other.

Skin-Care Ingredients That Shouldn’t Be Used Together

Retinol + Acne Treatments (Benzoyl Peroxide, Salicylic Acid)
The phrase less is more is very applicable here. “With the exception of Epiduo (which is prescription treatment specifically formulated to co-exist with retinol), benzoyl peroxide [and BHAs like salicylic acid] and retinoids should not be used together,” says Dr. Engelman. When they are, they deactivate each other, making them ineffective. 

Retinol + Glycolic/Lactic Acid 
Retinol and AHAs shouldn’t be combined as they can really dry out your skin and increase its sensitivity. “It is important to avoid using too many active products that could be overworking the skin and breaking down the bonds of healthy cells,” says Dr. Engelman. “There is, however, no evidence to support them deactivating each other.”

Retinol + Sun (UV rays)
Retinol is so effective because it increases cellular turnover on the skin’s surface, revealing younger cells. With this in mind, Dr. Engelman, advises taking extra precautions in the sun. “New skin can easily be irritated or sensitive when exposed to harsh UVA/UVB rays.” This is another reason retinol should be used at night before bed instead of in the morning, when skin is more likely to be exposed to sunlight.

Citric Acid + Vitamin C
Vitamin C is a potent antioxidant that is known to help visibly brighten the skin, while citric acid falls under the AHA category and promotes skin peeling. Both can help you achieve a glowing complexion, but they shouldn’t be used together because they destabilize each other. You can use one at night and one in the morning, but Dr. Engelman cautions against it. “Over-exfoliation will expose skin, weaken skin-barrier function and could trigger inflammation,” she says. If the barrier function is damaged, skin becomes vulnerable to infection from microorganisms, such as bacteria and fungus, and leads to sensitivity and irritation.”

AHAs + BHAs
“AHAs are best for dry skin and anti-aging, while BHAs are best for addressing the appearance of acne such as large pores, blackheads and pimples,” says Dr. Engelman. But like any form of exfoliation, you should be careful not to overdo it. “I have patients who start using exfoliating pads and the results after the first use are so amazing that they use it every day. By day four, they come to me with dry, irritated skin and they blame the product.” The best way to avoid skin sensitivity when it comes to exfoliating is to start out slow, only using the product once a week, and building up frequency as your skin adjusts. “Over treating the skin make matters worse because excessive exfoliation can breakdown the stratum corneum, whose job is to be a barrier against pathogens,” says Dr. Engelman. “Even if the barrier function isn’t visibly damaged, the skin may experience a low amount of inflammation (called chronic inflammation), which over time prematurely ages skin.”

Vitamin C + AHAs (Glycolic Acid, Lactic Acid, Malic Acid, Citric Acid and Tartaric Acid)
Because AHAs chemically exfoliate the skin’s surface, like citric acid, they shouldn’t be combined with Vitamin C at the same time. “When used in conjunction, these ingredients cancel out the effects of one another or can be irritating to the skin, causing sensitivity and dryness,” says Dr. Engelman. "Vitamin C acts as an antioxidant and AHA chemically exfoliates, together these acids destabilize each other." Instead, she recommends using one in your morning routine and one at night.

Skin-Care Ingredients That Work Well Together

While certain skin-care ingredient combinations deactivate each other or can result in irritation, others are a match made in heaven. Ahead, Dr. Engelman gave us a breakdown on what skin-care ingredients work well together.

Green Tea and Resveratrol + Glycolic or Lactic Acid
Thanks to the anti-inflammatory properties in green tea and resveratrol, they pair well with AHAs. When used together, green tea or resveratrol can have a calming effect on skin’s surface after exfoliation, according to Dr. Engelman.

Retinol + Hyaluronic Acid
Because retinol can be slightly irritating and drying on the skin, hyaluronic acid can be a skin-saver. “Hyaluronic acid helps to hydrate the skin, combatting both the irritation and peeling,” says Dr. Engelman.

Benzoyl Peroxide + Salicylic or Glycolic Acids
Benzoyl peroxide is great for treating acne, while hydroxy acids are helpful in breaking down clogged pores and blackheads. Dr. Engelman explains it like this: “Using benzoyl peroxide is essentially like dropping a bomb to eradicate any acne and bacteria on your skin’s surface. Together, they can effectively treat acne.”

Peptides + Vitamin C
“Peptides help to hold cells together, while vitamin C works to reduce environmental stress,” says Dr. Engelman. “Together, they create a barrier for the skin, lock in moisture and ultimately work to improve texture long term.”

AHA/BHAs + Ceramides
Adding a restorative, hydrating ingredient to your skin-care routine whenever you’re exfoliating using AHAs or BHAs is key. “Ceramides help to restore the skin’s barrier by holding the cells. They lock in moisture and act as a barrier against pollution, bacteria and assailants,” says Dr. Engelman. “After using chemical exfoliants, you must add moisture back into the skin and protect the skin barrier, and ceramides are an effective way to do that.”

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Photos: Chaunte Vaughn