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The Reason Vitamin C Serum Can Darken Your Skin (And How to Stop It from Happening)

Serum staining your face and fingers? Here's what to know.
Vitamin C serum darkens skin

Ever used a vitamin C serum and noticed your skin looking darker, orange or more tanned? 

You're not alone—this is a known side effect of the popular brightening and anti-aging ingredient!

But could the colour change actually be harming your skin? And is there a way to stop it from happening in the first place? Here's a recent question from my inbox:

So, there are definitely some skincare ingredients to consider avoiding when you are getting a lot of sun exposure, at least during the daytime (if not altogether). Alpha-hydroxy acids such as glycolic acid and lactic acid are known to increase sun sensitivity. The same goes for retinoids, which are linked to phototoxicity, lipid peroxidation and DNA damage in UV light.

But vitamin C? It's an ingredient you can safely use year-round! In this article, I'll explain:

  • Why vitamin C is in fact beneficial when you're getting UV exposure
  • What causes vitamin C serums to darken your skin, and how to prevent it
  • Which vitamin C serums to try (and how to use them) to avoid this issue

How Vitamin C Protects Your Skin

Vitamin C serum darkens skin

Vitamin C scavenges free radicals and helps protect your skin from sun damage.

Truth be told, vitamin C is an ideal ingredient to use in the summertime, because that's when our skin is exposed to the most UV light—and therefore the most free radicals. 

Free radicals are toxic, unstable molecules that contribute to aging by depleting the natural antioxidants in our skin and causing cellular and DNA damage.

What vitamin C does, as an antioxidant, is:

  • Neutralize the oxidative stress caused by these free radicals
  • Protect against UV-induced skin damage 
  • Aid in skin repair

According to The Journal of Clinical and Aesthetic Dermatology, "sunscreens are only partially effective in blocking free radicals produced by UV exposure." (Shocking, right?!) So you should think of vitamin C as adding a secondary level of protection.

That's in addition to vitamin C's ability to brighten the skin, fade pigmentation, and (at least with L-ascorbic acid) promote collagen production!

What Causes Vitamin C to Darken Your Skin

Vitamin C serum darkens skin

An oxidized vitamin C serum (left) vs. a fresh vitamin C serum (right).

So, what's going on when a vitamin C serum makes your skin look darker?

There are two scenarios for why you might see a colour change, and both have to do with oxidation:

  1. The vitamin C has oxidized in the bottle
  2. The vitamin C has oxidized on the surface of your skin 

Here's what to know about each...

Vitamin C That Has Oxidized in the Bottle

Vitamin C serum darkens skin

An oxidized bottle of vitamin C (not only has the serum turned dark brown, but the rubber dropper has also started to dissolve).

After contact with light, heat and air, vitamin C eventually oxidizes and loses its potency. You'll know it when your serum changes colour, turning brown. (With L-ascorbic acid, this usually takes about three months after opening the bottle.)

The reason it can stain your skin is because vitamin C degrades into erythrulose—the EXACT ingredient you'll find in many self-tanners! DECIEM, for example, uses erythrulose in Hylamide Glow Radiance Booster and The Chemistry Brand "Glow" Oil. A tan from erythrulose can last as long as a week!

Far more worrisome than an unwanted tan, however, is that erythrulose may even age your skin. As I explained in my self-tanner tutorial, erythrulose and dihydroxyacetone (DHA) darken the skin via the "Maillard reaction." Similar to caramelizing meat, this process generates free radicals and could accelerate sun damage and DNA damage—exactly what we're trying to avoid in the first place by using vitamin C!

[Read more about how self-tanners can age your skin]

Best case, you won't any get results from applying a vitamin C serum that has oxidized in the bottle. Worst case, it could not only cause colour changes, but also backfire in terms of skin repair! 

Vitamin C That Has Oxidized on Your Skin

Vitamin C serum darkens skin

A fresh bottle of vitamin C (notice the clear liquid with a thin consistency).

But what if you're using a fresh, non-oxidized bottle of vitamin C, and still notice a change in skin colour by the end of the day (or when you wake up in the morning, if you apply your C at night)?

According to Dr. Zoe Diana Draelos in Dermatology Times, "vitamin C preparations can also discolour on the skin surface as they contact oxygen in the environment. This accounts for the orange colour that may emerge on the skin in the morning after wearing a vitamin C preparation overnight."

How to Stop Vitamin C from Darkening Your Skin

Fortunately, there are a few things you can do to prevent oxidized vitamin C from staining (not to mention wreaking havoc on your skin goals!):

Prevent Your L-Ascorbic Acid Serum from Oxidizing