How to know when your vitamin C serum has oxidised or expired

We love vitamin C serums for their ability to reduce the appearance of hyperpigmentation, protect our skin from free radicals (and therefore photoageing), and boost overall brightness and glow. Their only downfall, really, is that they have the stability of a Larry David character.

We’re taking you through the tell-tale signs of vitamin C oxidisation, what that means in terms of efficacy, and how to choose and store your serum for a full and potent shelf life (and super glowy skin!).

Eliminate exposure to the elements

More often than not, air, light and heat are they key culprits of vitamin C oxidisation. Notoriously difficult to formulate, vitamin C is typically unstable in water solutions, making serums with the ingredient particularly sensitive to the elements. Dark or opaque bottles (protecting from light), and droppers rather than pumps (protecting from air) help to increase on-shelf stability.

Cool, dark and consistent, your fridge is actually the best place to store your vitamin C serums – just don’t mistake them for salad dressing.

READ MORE: Expiration, contamination and curation: the ultimate guide to spring cleaning your beauty stash

Keep an eye on the colour of your serum

The easiest way to tell if your vitamin C serum has oxidised (and therefore lost most of its potency) is by its colour.

Many serums start yellow, some clear. If you’ve noticed that yours has developed into a much darker yellow, a deep amber, or even brown, this may be a sign of oxidisation, and can result in your serum no longer working as intended.

In the case of many serums, this colour-changing is inevitable. The time it takes to get there, however, will depend on how it has been formulated, packaged, or the way you have used and stored the serum. Our tip? Don’t wait too long after purchasing before using your new vitamin C serum.

Notice any scent or texture changes

If you haven’t noticed colour changes, you might notice a stronger, smokier scent, or a thicker consistency. These may come alongside colour changes too and are also signs of oxidisation.

It is unlikely that an oxidised or expired vitamin C serum will cause harm to your skin, so don’t stress if you’re reading this and only just realising your serum may not be in its best shape. It just means that you won’t be reaping its full brightening, evening, firming, and glow-inducing benefits (and that it’s time for a new bottle).

READ MORE: Everything you need to know about incorporating vitamin C into your skincare routine

The perks of a powder

Free from water, vitamin C powders have superior stability.

In order for your skin to benefit from vitamin C, it needs to be in a form called ascorbic acid. As we’ve mentioned, vitamin C, or ascorbic acid, is unstable and begins to degrade when exposed to heat, oxygen, or light. The ascorbic acid in powdered vitamin C is more resistant than other forms.

Enter the newest vitamin C serums on the block: goop’s GOOPGLOW 20% Vitamin C and Hyaluronic Acid Glow Serum, and Drunk Elephant’s C-Firma™ Fresh Day Serum, both of which require you to mix an L-ascorbic acid powder into a hydrating serum base.

This means the shelf life of your serum (about six months) starts on your first day of use, rather than the day it got bottled, and eliminates the risk of early oxidisation due to cargo/transportation, storage, or sitting in a steamy bathroom. It also ensures that your skin gets the most active, potent dose of vitamin C from the get-go.

Want to perfect your skincare routine? Ask MECCA! Chat live to our MECCA in-store experts, either online or by video call, who can help recommend the best products and ingredients for your skin type and concerns. We're your beauty best friend on call – just click the speech bubble icon in the bottom right corner of your screen.

Shop our favourite vitamin C serums below:


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