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Vitamin C Skincare – C is for Complicated

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vitamin c skincare

Vitamin C Skincare Benefits

Vitamin C skincare has many benefits. Including providing antioxidant protection, reducing hyperpigmentation, improving skin laxity, improving skin tone and helping to synthesis collagen.

No wonder it’s a star ingredient in many skincare lines. In fact, some brands have entire ranges built around this single ingredient.

By now we all know that Vitamin C skincare products have amazing benefits for our skin. However I don’t want to just repeat what many other blogs have covered before me. So I won’t be going into the benefits of Vitamin C skincare too deeply.

Not Another Blog Post About Vitamin C

Since introducing Osmosis skincare to my treatment menu I have been introduced to a new concept in utilising Vitamin C skincare that goes against what we (myself included) have taken as gospel for many years. In particular their Catalyst Plus and Catalyst AC-11 products.

Not one to follow things blindly and always looking to learn more, I have done my own research. My findings are quite interesting!

One brand in particular, with fairly simple formulations (some may say quite ordinary in fact), love to push certain scientific facts for their own agenda. Priding themselves on being clinical and educating the end consumer. However in the process everyone now thinks they’re cosmetic scientists! As a full disclaimer, I am not a cosmetic scientist. I am a Facilaist. But I know enough to know that formulation is king and you can’t single out pieces of evidence while over-looking others.

So in this blog post I want to demystify a couple of key points about Vitamin C skincare. In particular to the type of Vitamin C we should be using. Why we really shouldn’t focus on percentages. And the big one, whether oxidised Vitamin C skincare is good, bad or ugly (depending on whether you like orange or not).

L-Ascorbic Acid – The Gold Standard in Vitamin C Skincare?

L-Ascorbic Acid is the naturally occurring and most bio-available form of Vitamin C. Meaning that its the form our cells need in order to utilise it. The skin also doesn’t need to do any form of conversion. It’s also water-soluble so works within the water proportion of the cells (as opposed to the lipid membrane).

The problem with L-Ascorbic Acid however is its a highly unstable ingredient so can be challenging to work with in formulations. Particularly in aqueous solutions (containing water) as it begins to oxidise. Which we are lead to believe is bad for the skin.

L-Ascrobic Acid can also be highly irritating on the skin. It is after all an acid (the clues in the name) and works best at a low pH of 3.5 or below.

All of this is probably familiar to your already. After all certain brands have created a number of Vitamin C skincare products that are either water-less (therefore more stable) OR utilise more stable forms of Vitamin C that are lipid soluble.


The Problem With L-Ascrobic Acid

What isn’t often talked about however is the fact that L-Ascorbic Acid is water soluble and this of course affects absorption. Remember that our skin has a lipid bi-layer structure. Therefore water-soluble ingredients such as L-Ascrobic Acid have difficulty being absorbed into the skin and permeation is slow. For example, it has been reported that only about 12% of the AA in a topically applied 10% solution was absorbed after 72 hours [4].

Skincare brands know this of course. So to increase the chances of absorption they simply increase the percentage of L-Ascrobic Acid in the product. There are two problems with this. Firstly, the more ‘acid’ you add the more irritating the product is going to be. Therefore the more chance of adverse reaction.

Secondly, there is a cut off point as to how much is effective and this was proven in a scientific study [1]. The study found the maximal absorption was achieved with a 20% vitamin C solution, with higher concentrations over 20% resulting in lower absorption. Yet brands insist on appealing to our ‘more is better’ nature and adding up to 30% L-Ascorbic Acid even though it’s clinically proven to be less effective than a 20% solution.

One of the ways to increase absorption of Vitamin C into the skin is exfoliation. As this removes part of the stratum corneum which acts as the barrier preventing optimal absorption. However I would not advisable as a long term, daily solution! Solutions also need to have a low pH at 3.5 or below, in order for the ionic charge on the molecule to be removed and allow transportation across the stratum corneum.

Oxidised VS Degraded

Now this is where my research got interesting. We all know that oxidised Vitamin C is bad and doesn’t work. Right? In fact some brands even claim that oxidised Vitamin C is actually a pro-oxidant (the opposite of an antioxidant), meaning it would cause free radical damage.

By the way, there is absolutely no scientific evidence to support this claim. At least not that I could find. It’s all based on theory. Vitamin C has only been shown to act as a pro-oxidant when overdoses are orally ingested in supplement form. Therefore based on this theory, then it would be more likely to be excessive doses of Vitamin C to have a pro-oxidant effect. Not an oxidised Vitamin C. Maybe thats why absorption and effectiveness of Ascorbic Acid seem to peak at 20%?

The idea that oxidised Vitamin C is some how ineffective is completely false. Firstly when L-Ascorbic Acid oxidises in a water solution it changes chemically, converting to Dehydroascrobic Acid (DHAA).

Here’s a few key facts about Dehydroascrobic Acid and why we may have misjudged “oxidised” to mean “degraded” and somehow ineffective.

Dehydroascrobic Acid In Skincare

Interesting about 50% of the vitamin C found in normal skin is Dehydroascrobic Acid [3], therefore vitamin C uptake in the form of DHAA may be very significant in skin cells.

Also the results of a study show that Dehydroascrobic Acid permeates stratum corneum at a rate up to 12 times faster than L-Ascrobic Acid [3].

Really interesting is the finding that Dehydroascorbic acid at 4% showed a significant improvement in smoothing of the skin, skin elasticity, firming, disappearance of black and white heads, liver spots, pigmentation and healing acne and acne scars. In a separate study, Dehydroascorbic acid at 12% is tested for its effectiveness in stimulated reproduction of collagen in the forearm between the wrist and elbow.

This supports the concept that lower concentrations of DHAA in topical preparations can enhance skin vitamin C levels with less potential for side effects.

I’m not sure why the second study was carried out on the forearm and not the face but I think its fair to presume based on the 4% study that the same effects would be seen in facial skin.

Now ask yourself the question, if oxidised Vitamin C was “degraded”, “ineffective” and potential damaging to the skin in the form of a “pro-oxidant” as some brand claim. Then how are the scientific studies finding such good results from using oxidised Vitamin C topically?

Another finding is that our body can actually recycle Ascrobic Acid. It can also convert Dehydroascorbic acid back into Ascorbic Acid by the enzyme Dehydroascorbic Acid Reductase in the presence of glutathione [5]. Which is pretty cool!

Summary About Vitamin C Skincare

In summary, the information we’ve been told about oxidised Vitamin C in skincare does not seem to add up against the above scientific studies. Yet, they seem to be ignored by some skincare brands.

Don’t be tempted to go for high percentage Ascorbic Acid products. Not only are they more likely to cause irritation which is extremely bad for the health of the skin barrier. They’re also proven to be less effective. When it comes to Vitamin C less is actually more. If using L-Ascorbic Acid then 20% should be the maximum. Less if you have a sensitive skin.

Also don’t be put off by water-based Vitamin C serums. Formulation is king, so look for other any antioxidants, amino acids and minerals within the formulation that can help support the Vitamin C and keep it active but you needed worry if the product is slightly yellow or orange. It turns out it is still safe and effective to use after all.

One final thought. While its true that L-Ascorbic Acid is the most active form of Vitamin C and that it is most stable in powder form. It really doesn’t matter how stable something is if you can’t get it into the skin is high doses without causing irritation and delivering it to the living cells, where is can do its job. Using low doses, little and often, without irritating or inflaming the skin is the best way of getting Vitamin C in to the skin.


Following publishing this article it caught the attend of DECIEM, owners of global skincare brands including NIOD and The Ordinary. Who have been very prominent in the promotion of using only water-less formulations for L-Ascrobic Acid and been very vocal about not using products that contain water and L-Ascorbic Acid together.

Their team of bio-chemists reviewed my article and also the clinical data in which I referenced and published this article in response – “A Discussion of L-Ascorbic Acid and Dehydroascorbic Acid in Skincare

In the interest of being objective and giving both sides of the story I feel it’s only right to link to the article and give it the platform it deserves and so that you, the reader, can also weight up the pros and cons.

In summary the article outlines that L-Ascorbic Acid is the most potent, bio-available and also most studies form of Vitamin C. Which is absolute fact and something I never protested in my article. They also, quite rightly so, mention that L-Ascrobic Acid does oxidise to Dehydroascorbic acid, but then eventually to Diketogulonic Acid. Diketogulonic Acid can’t be converted back to L-Ascorbic Acid, as in the case of Dehydroascorbic acid. But no where do they mention that Diketogulonic Acid is a pro-oxidant i.e. promotes free radical damage. Which seems to feature quite prominently in their marketing.

I mentioned that glutatione is used to convert Dehydroascorbic acid back to L-Ascorbic Acid. They pointed out, again rightly so, that as we age our l-glutatione stores deplete. But there are products available with l-glutatione in them also, so this point for me is irrelevant.

I completely understand and respect their view point. After all, I myself for many years have advocated using pure l-ascrobic acid in the form of Vitamin C Mixing Crystals and I use a L-Ascorbic Acid, D-Alpha-Tocopherol and L-Glutathione powder blend in my treatments. I’m not objecting that pure L-Ascorbic Acid is the best form of Vitamin C and best stored in powder form. But we can’t ignore the fact that there are products on the market that do contain L-Ascorbic Acid and water together, yet still very effective and have clinical trials to support them (Osmosis and SkinCeuticals are two that spring to mind). So I’m still not 100% convinced that it’s as black and white, as one way is good and the other bad.

Where my view point is different however, as a Facialist, I don’t believe in treating the dermis at the detriment to the epidermis. Using high doses of an acidic ingredient on the stratum corneum causes irritation. Irritation triggers the bodies inflammatory cascade, which as a by-product generates free radicals. Free radicals cause lipid peroxidation and leads to a disrupted skin barrier. I believe the integrity of the skins barrier should always be preserved. This is my personal view and I understand there are different methods within the skincare industry.

What does sound promising though is The Ordinary releasing a 100% pure L-Ascorbic Acid powder. Now this I am interested in trying and will happily promote to clients. Using it in this format allows you to tailor how much or how little is right for your skin type and can easily be freshly diluted into your serums.

I would like to thank DECIEM and their team of biochemists for taking the time to read my post and write a very detailed and informative response. Also for being open to discussion and understanding different view points. You have my upmost respect! (and I look forward to trying your Vitamin C powder when its released).


1.  Pinnell SR, Yang H, Omar M, et al. Topical L-ascorbic acid: percutaneous absorption studies. Dermatol Surg 2001;27:137-142.  (PubMed)

2. Keller KL, Fenske NA (1998) Uses of vitamins A, C, and E and related compounds in dermatology: a review. J Am Acad Dermatol 39: 611-625.

3. Topical Dehydroascorbic Acid (Oxidized Vitamin C) Permeates Stratum Corneum More Rapidly Than Ascorbic Acid (Researchgate)

4. Dehydroascorbic acid (DHA)(*) 12% concentration regained the youthfulness of forearm between the wrist and elbow in stimulated reproduction of collagen against skin sagging due to aging progression.

5. Savini I, Duflot S, Avigliano L (2000) Dehydroascorbic acid uptake in a human keratinocyte cell line (HaCaT) is glutathione-independent. The Biochemical journal 345 Pt 3: 665-672.

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About The Author
Andy Millward

Andy is a qualified facialist, advanced skin aesthetician and beauty writer with a passion for all things skin and a keen interest in health, nutrition and wellbeing.

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