Wondering When To Use Vitamin C Serum? A Derm Weighs In

Ask any dermatologist what the most important active ingredients to include in your skin care routine are and vitamin C will be one of their answers. Simply put, vitamin C is the holy grail of antioxidants—but when should you start using a vitamin C serum? The potent antioxidant is a game-changer for treating hyperpigmentation and boosting collagen production, but when is it time to start including the powerhouse anti-ager in your routine?

“I usually recommend people start in their 30s, when natural antioxidant defenses in the skin start to decline,” says Dr. Joshua Zeichner, MD, associate professor of dermatology at Mount Sinai Hospital in New York City.

There are endless benefits of vitamin C serum: If you feel like your skin is showing signs of aging, such as uneven skin tone, rough skin texture, pigmentation, or oxidative stress from sun exposure or even sunburn, it may be time to protect yourself from those UV rays and supplement your skin care routine with a vitamin C product.

While shopping for vitamin C for skin, you’ll likely notice that one of its key traits is brightening skin. “It blocks a key enzyme involved in the production of excess melanin,” explains Zeichner, which is why it’s able to treat those hyperpigmentation blemishes so effectively.

So, the benefits of vitamin C include treating dark spots, fine lines, and wrinkles—what more could you want out of a product?

If you’re wondering when to use vitamin C serum to promote a healthy skin care routine, we’ve got answers. From when in your routine to implement the active to what you shouldn’t mix with vitamin C, Zeichner weighs in on everything you need to know. Read on for all the tips.

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When should vitamin C be used in your skin care routine?

You should use vitamin C all year round. With summer right around the corner, if you don’t already use a vitamin C serum, now is the time to implement one (antioxidants help neutralize free radicals, which helps protect the skin from environmental damage, Zeichner explains). Though free radical damage can happen all year long, it’s especially common during the summer months to have increased exposure to UV rays from the sun, leading to more free radical damage.

Apply vitamin C in the mornings to protect your skin and prevent environmental damage, recommends Zeichner. “There is data to suggest that applying vitamin C at night is also beneficial to the skin, as UV light damage can have long lasting effects even hours after exposure,” he adds, so you may still be able to reap the benefits of the ingredient. However, most people just apply it in the morning as part of their daytime skin care routine.

In the mornings, after washing your face with a gentle cleanser, apply a few drops of your vitamin C serum to your face. You’ll find many of these serums are boosted with additional hydrating ingredients, so if you have super dry skin, follow with a moisturizer and SPF. Some can skip moisturizer and go straight to the SPF (make sure you’re protecting yourself from sun damage by applying a broad-spectrum sunscreen that’s at least SPF 30). You can wear vitamin C serum under makeup, so feel free to finish up your makeup routine after that.

Courtesy of brand

Cetaphil Face Wash

$15 $13

Amazon

Courtesy of brand

La Roche-Posay Anthelios Mineral Ultra-Light Face Sunscreen SPF 50

$40

Amazon

$38

Ulta

What shouldn’t you mix with vitamin C?

Though vitamin C is part of a gold standard anti-aging skin care routine, you want to be conscious of how you’re using it. The powerful antioxidant can come with side effects: It “has the potential to cause skin irritation,” says Zeichner.

A good rule of thumb is that it “should not be combined with other actives that are also irritating, as the combination may cause a reaction in the skin,” explains Dr. Zeichner. “Avoid layering vitamin C with retinol, hydroxy acids, or benzoyl peroxide.” So, if you’re using vitamin C in your morning routine, use your retinol, physical exfoliator, or other exfoliating actives in the evening.

If you have sensitive skin or are experiencing irritation or redness on your face, consider using these actives less often, like three times per week, and gradually build up tolerance. “It is okay to use vitamin C daily, so long as you are not irritated by it,” he says. “If you develop redness, burning, or stinging, hold off a day or two.”

Seeing formulations on the market that contain vitamin C plus an exfoliating acid or other active ingredient? Take note that some may be formulated this way “to offer synergistic benefits, but these products have been pre-formulated and safety tested,” says Zeichner. “When separate products are combined, especially at higher concentrations, they are more likely to cause irritation.” You’ll often see formulas include ingredients like ferulic acid, hyaluronic acid, vitamin E, and niacinamide alongside the vitamin C to help boost the effects or provide additional hydration.

How do you choose a vitamin C serum?

In skin care products, topical vitamin C comes in two forms: as pure ascorbic acid or in its ester form, explains Zeichner. “Pure ascorbic acid is more potent but more unstable and potentially irritating,” he says. If your skin has a high tolerance for vitamin C or you want stronger antioxidant power, look for ‘ascorbic acid’ or ‘l-ascorbic acid’ on the label.

Meanwhile, “vitamin C esters like sodium ascorbyl phosphate and other compounds with the word ‘ascorbyl’ in them are more stable and better tolerated but less potent,” he continues. “They need to be converted into the active ascorbic acid by the skin after application.” He recommends dry and sensitive skin types use vitamin C esters.

As much as we love our vitamin C, the skincare ingredient can be a finicky one sometimes. “Pure vitamin C is a very temperamental ingredient that can easily be inactivated,” says Zeichner. Make sure your vitamin C serum comes in a dark or opaque bottle: “Pure ascorbic acid is particularly sensitive to changes in pH, temperature, and UV light. This is why pure ascorbic acid comes in opaque bottles, as UV will inactivate the molecule.”

Like with sunscreen, pay attention to the expiration date on the bottle. “The formulas tend to turn orange as the vitamin C oxidizes,” Zeichner says. “If you have a formula that does not look, smell, or feel as it did when you purchased it, toss it.”