When it comes to skincare products that deliver results, antioxidant serums with vitamin C are a standout. But knowing how and when to use a vitamin C serum is key to unlocking its full skin benefits.
“Vitamin C is an antioxidant that helps protect the skin from free radical damage. It can brighten the complexion, improve pigmentation issues and support collagen production,” explains board-certified dermatologist Dr Marisa Garshick. “You might notice results within three to four weeks, but full improvements often take three to six months.”
Below, the experts explain when to apply vitamin C serum in your routine, how it works, and what to watch for.
What does vitamin C do for your skin?
Shields your skin from environmental stressors
“Vitamin C is a powerful antioxidant that helps defend your skin from UV damage and environmental pollutants,” explains board-certified dermatologis Dr Janiene Luke. Antioxidants work by neutralising free radicals—unstable molecules produced when we’re exposed to things like UV rays, smog or smoke. “Free radicals can affect our DNA and activate enzymes that break down collagen in the skin,” she adds.
Using a vitamin C serum regularly can help protect your skin from this kind of stress, supporting healthier, more radiant skin in the long run.
Supports youthful-looking skin
Thanks to its antioxidant properties, topical vitamin C can help reduce visible signs of ageing by protecting skin from environmental stressors like sun exposure. It also plays a role in boosting collagen production, which naturally declines as we age. “Free radical damage breaks down collagen, and vitamin C helps slow that process,” explains Dr Luke. The result? Smoother skin and the gradual softening of fine lines and wrinkles.
Brightens and evens out your skin tone
Vitamin C serums are known for giving the skin a fresh, luminous glow. By supporting collagen and reducing abnormal pigmentation, they can help even out tone and fade dark spots over time. “You might start noticing improved texture and a subtle glow in a few weeks,” says Dr Luke, “but more noticeable results in brightness and tone tend to appear over several months of consistent use.”
When to use vitamin C serum
“Vitamin C is best used in the morning as it helps defend the skin from free radical damage triggered by daily environmental stressors,” says Dr Garshick. Applying it daily gives the most benefit, especially if you’re spending time outdoors or exposed to pollution.
While you can use it at night, experts agree that using it in the morning helps you get the most out of its protective effects and avoids potential conflicts with stronger nighttime ingredients.
What should you not mix with a vitamin C serum?
Vitamin C can be a skincare superstar, but it doesn’t always play nice with other active ingredients. “In general, it’s best not to layer vitamin C with harsh or potentially irritating products unless directed by a professional,” says Dr Garshick.
Some ingredients to avoid using at the same time include exfoliating acids like salicylic, glycolic and lactic acid; benzoyl peroxide; and retinoids. “These can irritate the skin on their own, and using them alongside vitamin C may make sensitivity worse,” adds Dr Luke. Plus, some can degrade or deactivate vitamin C altogether, making your serum less effective.
If you’re using these actives in your routine, save them for night-time, and use your vitamin C in the morning. Keep an eye on how your skin responds and back off if you notice any irritation.
How to use vitamin C serum
Vitamin C serum works best when applied in the morning after cleansing and before moisturising and sun protection, says Dr Garshick. “If you’re layering other serums, apply them from thinnest to thickest consistency.”
Here’s a simple morning routine:
- Gentle cleanser
- Vitamin C serum on clean, dry skin
- Hydrating serum (optional)
- Moisturiser
- Broad-spectrum sunscreen
How to choose a vitamin C serum
“Unfortunately, not all vitamin C products are created equally, so it can be confusing to try to find the right vitamin C to use,” Dr. Luke explains. However, there are a few key tips to keep in mind when shopping for the right vitamin C serum for you:
Type and concentration
L-ascorbic acid is the most well-studied and commonly used form of vitamin C in skincare. Serums with 15–20% L-ascorbic acid tend to deliver the best results. Some formulas also include more stable derivatives like tetrahexyldecyl ascorbate (THD), which penetrates deeply and suits sensitive skin.
Packaging
L-ascorbic acid is prone to oxidation, which means it can degrade when exposed to air or light. Look for serums in airtight pumps or amber-coloured bottles to help maintain potency.
Supporting ingredients
Vitamin C is even more effective when paired with stabilising antioxidants like vitamin E or ferulic acid. These ingredients help boost its benefits and keep the formula stable longer.
Possible side effects of using vitamin C serum
While vitamin C is generally well tolerated, some people—especially those with sensitive skin—may notice irritation, redness or dryness. Dr Luke suggests doing a patch test first: apply a small amount to the jawline or just in front of the ear and wait 24 hours. If no reaction occurs, you can use it on the full face. You can also start by applying it a few days a week, then gradually build up to daily use as your skin adjusts.
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