Vitamin C is a pretty trendy ingredient right now for cosmetics, but what should you know when your purchasing or formulating products with it? Notoriously unstable in formulation, what steps can you take to ensure you’ve got a good product with functional vitamin C? How does vitamin C impact the health of your skin? How does it function in a formulation? What are the forms out there? In this blog post, we’ll go through all these questions and more. Warning, this post is quite technical, but a thorough dive into the topic for anyone looking for these details. Enjoy!
What is vitamin C?
Vitamin C, otherwise known as ascorbic acid and L-ascorbic acid, is a water-soluble vitamin found in lots of different foods, especially fruits and veggies. Ascorbic acid is a weak sugar acid that’s structurally related to glucose. Overall, vitamin C is a very important antioxidant and is required for several important body functions, such as in our immune system and tissue repair following an injury. Unlike plants and certain animals, due to the lack of an enzyme, humans are unable to make vitamin C in our bodies. As a result, getting enough through the diet is super important. Aside from protecting you from things like scurvy and lowering your risks for different chronic diseases, vitamin C also plays a big role in the health of your skin.
Vitamin C and Skin Health
Vitamin C is the most abundant antioxidant in the skin and plays an important role in its health, easily demonstrated by the impacts of deficiency, which is linked with impaired wound healing, UV damage, fragile skin and more. Normal skin, surprisingly, has a very high content of vitamin C, at comparable levels to other areas of the body. More surprising than that, the epidermis, the outer layer of your skin, has more vitamin C in it compared to the dermis, with differences between 2-5 fold between the two layers being consistently reported. Why is this surprising? The epidermis is characterized by a lack of blood vessels, the normal delivery method for nutrients throughout the body, whereas the dermis still has blood vessels throughout. The high concentration at the epidermis would mean that vitamin C actively diffuses here, which is a pretty good indication that this vitamin has an important role to play for skin health. Vitamin C is important for collagen formation, scavenging free radicals, stopping melanogenesis (i.e. age spots and hyperpigmentation), wound healing, and lots more. As you can probably imagine, all of this can have a big impact on how your skin looks as you age.
Throughout the course of your life, your skin is exposed to a number of different challenges, which in turn result in oxidative stress (free radicals) - think harsh weather, pollution, sun exposure, and harsh beauty products. These challenges are linked with depletion of vitamin C levels in your epidermis. As you age, vitamin C levels in your skin will lower, but your lifestyle can seriously compound this. For example, sun exposure and smoking have both been demonstrated to markedly reduce vitamin C in your skin (as well as throughout your body, in the case of smoking). On the flip side, it’s been well documented that vitamin C is able to limit sun damage, which is an oxidative process… this all makes a lot of sense when you think about how antioxidants generally act in the body (diagram below).
Source: Research Gate
Having sufficient levels of vitamin C throughout your body, which you can get through your diet, seems to do the job at making sure you’ve got good levels in your skin. The old adage that beauty comes from within couldn’t ring any truer here. Having a healthy lifestyle and good nutrition generally bodes well for having healthy looking skin.
Vitamin C Interventions - Supplements and Topical products - what’s the evidence?
Here’s a quick rundown of the available evidence that I felt had sufficient enough significance and weight to mention.
- 2 human studies have demonstrated an increase in skin vitamin C following supplementation. Note, neither adequately measured blood vitamin C levels before and after the study. In a study that measured vitamin C in buccal keratinocytes of the skin, the vitamin C concentration doubled after supplementation with 3g/day (significantly higher than the recommended daily intake) for 6 weeks. In a study by Nusgens and colleagues, skin levels of vitamin C didn’t increase further after ‘plasma saturation was reached’ - i.e. once your cells have enough vitamin C, you’re not going to be able to get any more in there.
- In a recent systematic review of studies, they found that intervention with vitamin C intake was associated with improvements in skin elasticity, facial wrinkling, roughness, and color. These interventions where either via vitamin C from supplements or from the diet, fruits, and veggies.
- It’s well established that vitamin C limits damage from sun exposure, as this injury is mediated by free radicals/oxidation. Demonstrated both in cell and animal studies with both topical and dietary intake of vitamin C. Note, vitamin C was only minimally effective on its own. Studies with the best results used multiple components, notably vitamin E has a synergistic effect that is particularly effective. *Efficacy depended on the pre-existing vitamin C status of the skin*.
- One study suggested that when health status was already optimal, there was no absorption of vitamin C following topical application.
- There has not been convincing evidence that vitamin C topically or via supplements noticeably reduces wrinkles, although research here has been restricted by technology with actually measuring this until recently. There is an indication that improved vitamin C status can improve collagen production, which ultimately may improve wrinkles… but only if the person has deficient stores. Impacts where significant in smokers, compared with non-smokers with sufficient vitamin C already.
- One study showed that supplementation with both vitamin c and e improved the rate of wound healing in children with extensive burns. Again, this was only seen when vitamin C levels were deficient.
Vitamin C has been demonstrated to impact the look of the skin, especially regarding hyperpigmentation, and wound healing.
Like many other nutrients, it appears that vitamin C levels in the skin respond to blood vitamin C levels.
Vitamin C in cosmetic products
All of the above evidence aside, there are some big challenges when trying to incorporate vitamin C into your cosmetic products. The main one - many of the forms the vitamin comes in are very unstable and react readily when exposed to air or sunlight. I see this SO FREQUENTLY in products on the market claiming to have vitamin C in them. By the time they come into the hands of their customers, all the vitamin C has reacted, rendering that claim pure marketing. Have you ever bought a vitamin C product that came to you, or even throughout its life tuned, a golden to brownish color? That’s what generally happens when the vitamin C oxidizes. When you’re purchasing a vitamin C product, this is something to look for to make sure there’s some vitamin C left in it for your skin’s benefit. So what are the forms of vitamin C out there for cosmetics and how can we overcome this stability challenge?
The first and most popular form of the vitamin is L-ascorbic acid, the most biologically active and well studied. It’s water-soluble and very unstable - aside from product stability, this also results in a harder time penetrating the more fatty skin of your stratum corneum, the outer layer of the skin. L-ascorbic acid is also a charged molecule, which further reduces its ability to penetrate the skin. As a water-soluble and charged molecule, L-ascorbic acid is repelled by the skin overall. For cosmetic products, you can enhance this forms stability and ability to penetrate by lowering the pH of the product to below 3.5 (note, the pH of your skin is closer to 5.4, so this would be quite acidic). This improvement is largely because it transforms L-ascorbic acid from charged to uncharged. An example of a stabilized L-ascorbic acid product on the market is SkinCeuticals by L’Oreal, which achieved this by both a low product pH as well as the addition of ferulic acid, which further stabilized the vitamin (note, this is a patented technique). Other than that, my experience reviewing products with L-ascorbic acid in them overall is, way too many of the products I’ve seen with this ingredient are oxidized… again, having the oxidized ingredient in the product - not going to do much for your skin. To add to this, most everyday products will want to achieve a pH closer to 5.4, which is very problematic for vitamin C. pH adjusting L-ascorbic acid products to be more suitable to the pH of your skin will ensure that the L-ascorbic acid oxidizes and doesn’t penetrate.
Controversy in the cosmetics industry over vitamin C, this past year the company Drunk Elephant was sued by L’Oreal for patent infringement over SkinCeuticals mentioned above. Check out Vox’s coverage of the story here.
There has been lots of work put into the development of ascorbic acid derivatives for skincare to make them more stable and less likely to oxidize, especially at a pH closer to 5.4. Note, in order for them to be effective, these forms must be able to convert to ascorbic acid on application. One of the ways to stabilize vitamin C is by adding a phosphate group - these forms demonstrably are able to convert to ascorbic acid on application, although at a slow rate. Ascorbyl Glucoside, for example, has better stability and can penetrate the skin, but the conversation rate to ascorbic acid is still unknown. Derivatives with fat-soluble parts, like palmitate in the case of L-ascorbyl palmitate, are able to further assist delivery - animal studies here demonstrate an increase in uptake, although more research needs to be done to verify the conversion rate to ascorbic acid. Two other topical forms include ascorbyl-6-palmitate and magnesium ascorbyl phosphate. Unlike l-ascorbic acid, which is water-soluble and unstable, both of these are fat soluble, esterified forms that are stable at a neutral pH. Moreover, recent studies suggest that encapsulated molecules may be able to improve vitamin C penetration to the lower levels of the skin even more. I think at this point it’s worth bringing up the elephant in the room… efficacy for vitamin C products, in whichever form they come in, will be dependent on the vitamin C levels of the individual. If they’re already full up on their vitamin C, i.e. getting enough through their diet and taking good care of their skin, topical vitamin C won’t have a big impact.
What kind of dosage should you be looking for in your products? Ultimately, it seems that the optimal amount of vitamin C is dependent on the formulation. For example, if your using L-ascorbic acid, there’s pretty much no point of having any unless you’re bringing the final product pH below 4 and taking all the other steps to keep your product stable, such as putting the product in an airless tube and avoiding transparent packaging where the product is exposed to light. To add to that, formulations that are most effective incorporate other antioxidants, particularly vitamin E. In most cases, for a product to have significant vitamin C impacts, it seems that concentrations should be higher than 8%. Note, a recent clinical study with 3% vitamin C product used over a 4-month period showed a significant increase in skin vitamin C, and there have been quite a few other studies showing impacts at 5% and lower. Studies that looked at products with percentages over 20% usually came back as no more helpful than concentrations below. To add, these very high percentages had a higher likelihood of causing skin irritation. Overall, it seems that percentages between 10-20% will give you the best bang for your buck.
That’s a wrap! Questions, queries, conundrums or concerns? Leave em below or on any of our social media pages!
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