Why Vitamin C Goes Bad and How to Prevent It?

What is vitamin C oxidation, and why does it happen to some of our beauty and skincare products? Does this impact our skin, and how do we prevent it? 

Vitamin C is a popular ingredient for brightening the skin, wound healing, and imparting antioxidant properties to the skin. Vitamin C can even boost sunscreen. However, vitamin C or L-ascorbic acid can be a bit finicky or unstable. When it comes into contact with oxygen, it breaks down easily, and can very rapidly become rancid. 

So, how do we know if our vitamin C has gone bad?

To provide an example, the Juice Beauty Blemish Clearing Serum was a product that Cassandra used for years, and yes, it has tons of vitamin C. Back when Cassandra was struggling with her acne, it was a product that she deeply found comfort in. It was an extremely effective serum, especially for nighttime use. She greatly attributes it to helping her skin. However, she came across one that just chilling in the back of the cabinet, it had turned brown, and she saw that the expiration was 2016! 

Juice Beauty Clearing Serum -$28

This product is now repackaged, and the white coating actually stops light from penetrating the bottle if it’s kept by a window.

Vitamin C that has turned brown is not technically dangerous, but it is much less effective. Brown vitamin C means that the preservatives are breaking down. So, there could be other stuff growing in it. Vitamin C's are supposed to be a little bit yellow or a little bit milky, so as soon as they start to change color, they are oxidizing. It may also start to smell different, but fragrance may mask the smell of oxidation. So, color is the best way to tell. 

As mentioned before, products have an expiration date. When you look at the bottom, and it says “best buy” this date,” you might want to make a note of that and write it on the bottom of your products. 

How do you store vitamin C?

To prevent it from degrading too fast, it should be kept in a dark, oxygen-less, and heat-less environment. The best place to store your vitamin C serums is in a dark, temperate area. You don't want vitamin C to sit directly in the sun, in the car, or in a bathroom where it can be exposed to heat from the shower. You also don’t want to give it too much exposure to cool air conditioning. Keeping it out of these environments will keep it stable. Another thing that can keep vitamin C stable for longer is the packaging. 

Some brands like The Ordinary actually have  UV protective packing. That’s why you’ll see darkened glass for certain vitamin C serums. However,  some like the ginger vitamin C shot from Sweet chef do not. So, when vitamin C is not kept in UV protective packaging, it’s especially important to keep it in a cool dark area. 

The Ordinary Ascorbyl Glucoside Solution 12% -$11



You can also keep your skincare in a regular or skincare fridge. Water-based products are also great to keep in the fridge.  

What ingredients make a vitamin C product formula more stabilized?

Some vitamin C formulas are stabilized already and don't need a light sealed container. An example of this is the Dear Klairs vitamin C. Cassandra loves this one, and it’s in her routine. It does not come in a darker container either. Some vitamin C formulas do not need  UV protective packaging because they include ingredients like folic acid or vitamin E which can help stabilize vitamin C. So, finding vitamin C products that have a vitamin E or for like one are good options for stable vitamin C products.

Dear, Klairs Freshly Juiced Vitamin Drop - $23



Radish fermented filtrate and honey sample Japanese honeysuckle can be used to preserve vitamin C products, but they are not as effective as oxy ethanol, methylparaben, or polycarbonate, etc. Even though EWG likes to fearmonger around these ingredients,  there have been a lot of studies on these molecules that show their effectiveness, and Cassandra doesn’t mind using them in her routine. 

What is oxidation?

Basically, the molecules within the vitamin C start giving up electrons. Think about it like cutting an apple and leaving it out on the counter. It turns brown because the oxygen from the air is actually causing the apple or that avocado to brown.  On the other hand, this is why Vitamin C is such a great antioxidant for our skin. It basically inhibits the oxidation from happening on our skin. Our skin is constantly bombarded by pollutants like dirt, irritants, and free radicals. Therefore, antioxidants give themselves up so that your skin doesn't have to give itself up. 

Also, here are some more of Cassandra’s favorite vitamin C products!

Sweet Chef Ginger + Vitamin C Serum -$20


Pacifica Glow Baby Vitamin C -$20


Glossier Super Glow Magnesium Vitamin C Serum -$28


Beauty Pie Vitamin C Capsules -

Jumiso Vitamin C - $22.79

Indeed Labs Vitamin C -$19.99

Covey Vitamin C -$59

Wander Beauty Vitamin C -$42


The Ordinary Ascorbic Acid 8% + Alpha Arbutin 2% Vitamin C -$11


Inkey List EGF Vitamin C -$14.99

Coverphoto cred: @ALLMAKEUPT