Colour changing cocktails are fun, but... colour changing skincare? Should you be sold? Is it a quirk? If your vitamin C serum turns yellow-brown after a month - will it still work? When a vitamin C serum turns yellow-brown is it like the yummy brown crust of a homemade loaf or the suspicious yellow-brown crusting deodorant causes on the underarms of all your white T-shirts? My friend, Let's find out...

Is Your Vitamin C Serum Still Potent If It Turns Yellow-Brown?

In Being Savvy at Skincare, Buzz skincare ingredients by Cheryl WoodmanLeave a Comment

Colour changing cocktails are fun, but… colour changing skincare? Should you be sold? Is it a quirk? If your vitamin C serum turns yellow-brown after a month – will it still work?

When a vitamin C serum turns yellow-brown is it like the yummy brown crust of a homemade loaf or the suspicious  yellow-brown crusting deodorant causes on the underarms of all your white T-shirts?

My friend, let’s find out…

Colour changing cocktails are fun, but... colour changing skincare? Should you be sold? Is it a quirk? If your vitamin C serum turns yellow-brown after a month - will it still work? When a vitamin C serum turns yellow-brown is it like the yummy brown crust of a homemade loaf or the suspicious yellow-brown crusting deodorant causes on the underarms of all your white T-shirts? My friend, Let's find out...

What Colour Is Vitamin C Serum?

Rock your world moment – Vitamin C is not orange. Yes, you read right – vitamin C is not orange. Crazy huh? Dissolve up an ascorbic acid formula (the chemistry word for the skin active form of vitamin C) and it will be 100% clear. The colour of water.

Vitamin C and orange – It’s a hard association to kick ‘eh.

Vitamin C is famous for being found in citrus fruits. It’s exactly what saved sailors from scurvy back-in-the-day. Scurvy is a condition caused by vitamin C deficiency – without vitamin C collagen breaks down and everything your body makes collagen with e.g. skin, gums, soft tissues – bleeds and falls apart.

It’s why vitamin C is thought of as orange. You get a nice dose from an orange, so lots of supplements play into this association. Pick up a bottle of vitamin C tablets and what colour is the label? Develop a tickly throat and what colour fruit is your mum going to stock you up on?

Orange.

…but in reality, vitamin C dissolved into water is not orange. It’s clear. #BrainTwister

Which in turn means, your vitamin C serum should also be clear. So… why has your vitamin C serum turned yellow-brown?

Vitamin C Benefits for Skin

Vitamin C serum benefits skin in many ways. It’s an antioxidant (say goodbye to environmental ageing), it’s a collagen builder (say hello voluminous skin) and it’s a skin tone brightener (welcome that youthful glow). To bring all these benefits, vitamin C has to be in it’s vitamin C form – also known as L-ascorbic acid.

If you’ve investigated a few vitamin C serums you’ll probably have seen something like, ‘Vitamin C serum’ in large print and ‘15% L-ascorbic acid’ in small print at the bottom of the label. Just take a look at these examples;

The Ordinary boast 23% L-ascorbic acid, Paula’s choice 25% and SkinCeuticals 15% – but my friend, the potency is not all about percentage, it’s also about bioavailability and that means;

  • How well the overall formula delivers vitamin C into you skin e.g. the difference between holding a jumper and actually wearing it
  • The vitamin C serum shelf life e.g. how long the vitamin C is potent for

…and point 2 is what brings you here, because the thing is, nothing stays the same forever and vitamin C’s potency is also its largest catch. It’s such an effective anti-oxidant, it also likes to do-its-thing in the bottle.

When things oxidise, they age and in doing so, turn into something they weren’t before. Apples turn brown, carrot juice goes a muddy colour and meat looks like it’s cooked even though it’s not.

All 3 things look very different because chemistry has happened. Compounds have been changed. Something’s been used-up and in its place rests a new ingredient.

This is exactly what happens when vitamin C serums turn brown. Vitamin C has oxidised (reacted with oxygen) and turned into dehydro-L-ascorbic acid and eventually diketogulonic acid. You now no longer have an L-ascorbic acid serum, you now have a diketogulonic acid serum.

Are Yellow-Brown Vitamin C Serums Still Effective?

If your extremely warm and woolly winter jumper turned into threadbare sexy netting on one whole side – would it still be as effectively warm?

No. Very cute, but not as effective ‘eh.

Now, answer me this question my friend, I know you know the answer – you are too savvy. If your vitamin C serum turned yellow-brown, would it still be as effective, would it still have a full pack of vitamin C benefits for skin?

No… because the yellow-brown colour change is a visual sign of vitamin C chemistry. It shows that your vitamin C serum no longer just contains L-ascorbic acid, the skin active form of vitamin C.

It’s a sign that the 25% or 15% potency is reduced.

It could be reduced by 0.1% or it could be reduced by >10% or even 50%. How do you know?

Vitamin C Serum Shelf Life

Skincare companies by law have to determine the shelf life of all skincare products before they go on market. They do this by putting closed bottles of the new skincare product into huge walk in ovens at different temperatures – 25, 30, 40, 50 degrees Celsius. This speeds up the effect of ageing and the skincare company get to tell if their product is stable for 3 years without having to wait for 3 years – neat huh.

But… when you have a skincare product like vitamin C, it may well be stable for 3 years in a closed bottle, but when it’s opened and opened and opened for daily use, the shelf-life now becomes in-use life and your 3-year shelf life goes out the window.

See, every time you open a vitamin C serum, new oxygen gets into the ampule or tube. This is troublesome for all skincare ingredients and even more troublesome for vitamin C serums, because vitamin C gets on with oxygen like a house on fire – the 2 just can’t stay apart. They have chemistry and they’re using it.

When vitamin C and oxygen react, the new ingredients formed are yellow-brown in colour.

The more vitamin C there is in your serum, the clearer it will be. The more ‘oxidation products’ there are in your vitamin C serum the more brown it will be.

How to Tell an Oxidized Vitamin C Serum

To tell if your vitamin C serum is still potent, you need a vitamin C colour ruler. Luckily I have just the thing for you, or rather the team at Paula’s choice and FutureDerm do;

  • The Paula’s choice team, have shared this image of their vitamin C booster at different colours. Droplets 1, 2 and 3 still contain a very potent and skin active dose of vitamin C as L-ascorbic acid. Droplet 4 – does not. Droplet 4 is an overly oxidized vitamin C serum. If you have a vitamin C serum matching the colour of droplet 4, it’s time to bin it.

Now because this is manufacturer specific advice, I’m also sharing the results of an experiment my fellow skin scientist Nicki from FutureDerm performed;

  • In this experiment, Nicki has determined the % of vitamin C left in solutions of vitamin C with different colours. Click here to see the Futurederm vitamin C colour ruler. It tells you the exact colours to watch for, for when you have 100%, 80%, 60% and 50-40% of your quoted vitamin C concentration left. This ruler is very useful.

How to Keep Vitamin C Serum from Oxidizing

When your vitamin C serums turn yellow brown, vitamin C has oxidized. That means less of the vitamin C serum benefits are available for your skin – oxygen from the air has gobbled them up. So how exactly can you stop this from happening?

You can do this by limiting the magic 3 – heat, light and air.

All 3 of these factors promote oxidation.

  • Heat can be limited by never storing your vitamin C serum in a steamy bathroom. I also often get asked, ‘should vitamin C serum be refrigerated’ and although you shouldn’t have to, this is an easy win for prolonging the in-use life of your vitamin C serum.
  • Light can be minimised by storing your vitamin C skincare in a draw.
  • Air can be protected against by always remembering to replace the lid of your vitamin C skincare quickly… and tightly.

It’s also worth knowing certain formulations are better protected than others – now here fly’s in the SkinCeuticals vitamin C serum patent, the one warranting that hefty price tag;

Vitamin C can also be stabilised with other very effective antioxidants, vitamin E is a common partner but SkinCeuticals took this one step further and added a wonder anti-oxidant naturally found in wheat – ferulic acid. Ferulic acid is epically effective at stabilising vitamin C. The presence of this counter anti-oxidant preserves vitamin C serums in their active state, for longer. The reason for the gigantic/gold-standard price tag.


Have you used Vitamin C serums that have gotten to the overly oxidised yellow-brown colour? Are you concerned your vitamin C serum has lost potency? Are you refrigerating your vitamin C serum? Tell me all in the comments below… and if you have an epic vitamin C preserving trick up your sleeve, would you share it with the Honesty skin savvy community here? We are all ears…


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