Vitamin C in Focus: The Most Misused Antioxidant in Skincare

Welcome back, DERM Community!

If there’s one ingredient that has earned both cult status and clinical credibility, it’s Vitamin C.

We recommend it for pigmentation, photoaging, and antioxidant defense, yet it’s also one of the ingredients most patients (and clinicians) use wrong.

This week’s focus:

• The science of Vitamin C and why formulation matters more than concentration.
  

• Common patient mistakes that sabotage its benefits.
  

And a book pick that redefines how we think about “glow” from the inside out.

Featured on This Week’s Chapter:

The Science (and Fragility) of Vitamin C

Vitamin C, or L-ascorbic acid, is a powerful antioxidant that neutralizes free radicals and supports collagen synthesis.

But here’s the catch: it’s unstable.

Exposure to light, air, or improper pH rapidly oxidizes it, turning that golden serum into an inactive, irritating mess.

In dermatology, efficacy depends on three things:

• Form: L-ascorbic acid is the most active but least stable. Derivatives like magnesium ascorbyl phosphate are gentler but require conversion to become active.

• Concentration: More isn’t better. Studies show that 10–20% is the sweet spot for efficacy without irritation.

• pH: It must be acidic (around 3.0–3.5) for optimal skin penetration.
  

When those parameters are off, patients may be applying oxidized, ineffective, or even barrier-disruptive products.

Common Vitamin C Mistakes (and How to Fix Them)

1. Layering it wrong.
   Many apply Vitamin C after moisturizer or mix it with niacinamide, reducing absorption and altering pH.

   
   ✅ Fix: Apply Vitamin C on clean skin in the morning, before moisturizer and sunscreen.
   

2. Using it with incompatible actives.
   Retinol and strong acids can destabilize Vitamin C or increase irritation risk.

   
   ✅ Fix: Alternate, Vitamin C in the AM, retinol in the PM.
   

3. Ignoring oxidation signs.
   A serum turning dark orange or brown means it’s oxidized and potentially pro-oxidant.

   
   ✅ Fix: Store in a cool, dark place and replace every 3–6 months.
   

4. Overusing high concentrations.
   More isn’t more. High concentrations (25%+) can compromise the skin barrier, especially in sensitive or post-procedure patients.

   
   ✅ Fix: Stick to clinically backed ranges (10–20%) and buffer with hydration.
   

We’ve Put Together a Free Guide Just for You!

One practical, evidence-informed, and perfect guide for clinic education or patient take-home use on Vitamin C.

You won’t want to miss this:

Book Recommendation of the Week

“Skin Cleanse” by Adina Grigore

This book invites readers to rethink “more” in skincare, more steps, more actives, more irritation.

It’s a refreshing reminder that skin health thrives on consistency and simplicity, not chemical overload.

Inspiration of the Week

👋🏻 See you next Thursday, DERM community!

Thanks for joining us on Beneath the Surface.

Vitamin C may brighten, but clarity comes from understanding how and when to use it.

As you guide patients, remember that antioxidants don’t just fight oxidation, they reflect a mindset of prevention, patience, and protection.

Next week, we’ll be talking about perfect skins and what we can learn from those microbiomes.

Until then, stay balanced, stay evidence-based, and keep looking beneath the surface.

— The Derm for Primary Care Team