The Truth About Vitamin C Percentages

The Truth About Vitamin C Percentages

Ah, vitamin C. The sunshine vitamin! We all know the importance of vitamin C in our diet and in keeping us healthy, and recently it’s become an essential ingredient in skincare as well. This powerhouse antioxidant can combat sun damage, lighten pigmentation, and help promote smooth, plump skin. The problem is, there are tons of products on the market, with different forms of vitamin C and varying percentages. In this post we’ll try to demystify this vital ingredient and help you best utilize it in your skincare routine. 

The importance of vitamin C in skincare 

We want our skincare products to help promote a youthful feel and look with an even, clear complexion. We also want to protect our skin from environmental damage. Vitamin C is an essential ingredient for all three issues. 

As skin is exposed to the sun and other stressors through the years, skin becomes less resilient and “bouncy”. In particular, collagen production, which keeps your skin plump and youthful by providing structure and support to the skin similar to the springs in your mattress, slows down with time. Vitamin C is a cofactor for enzymes that build and link collagen fibers, and can also indirectly stimulate collagen production. While the sun’s UV rays can directly break down collagen (which is another reason your dermatologist is always nagging you about sunscreen!), vitamin C inhibits the enzymes that actively break down collagen. You can think of it as backstop for your sunscreen to protect your skin and keep it youthful. 

As time goes on, skin can develop brown spots and uneven pigmentation. Vitamin C helps even out the complexion by inhibiting activity of the enzyme tyrosinase, thereby reducing pigmentation development and fading dark spots. 

Finally, vitamin C is a powerful antioxidant and can help protect the skin from environmental stressors. When skin is exposed to pollution like smoke and smog, free radicals are created. These unstable molecules can bounce around and cause DNA damage in cells, leading to skin aging. Vitamin C can help neutralize these free radicals to reduce cell damage. 

Ok, so we know why vitamin C is important and how it can help the skin. What should we look for on product labels? 

You might think that a product labeled with a high percentage of vitamin C would be the best and most effective, but unfortunately, that’s not always the case! There are several important factors in addition to percentage that you should consider when looking for a vitamin C serum: the form of vitamin C, stability of the formula, and other supporting ingredients. 

Why the active form isn’t always the best 

The active form of vitamin C in the diet, and in the skin, is L-ascorbic acid. Unfortunately, taking high doses of vitamin C doesn’t make that available to our skin, so we need to apply it topically to see the benefit. All other forms of vitamin C are inactive and are converted within the skin to L-ascorbic acid. So why wouldn’t we want to always use L-ascorbic acid? Two main issues: instability, and irritation! 

In skincare, we prize vitamin C’s antioxidant properties. In fact, it’s such a good antioxidant that it will try to react with everything - light, water, oxygen, the container it’s in. As soon as you open the bottle, your product is exposed to heat, water, and light. Ever heard of those vitamin C serums turning brown on store shelves or a few weeks after you buy it? That’s the vitamin C breaking down before it ever reaches your skin. Because L-ascorbic acid is so inherently unstable, products using this form of vitamin C need to be packaged carefully, ideally in an airless, opaque pump; the product needs to have stabilizers (like ferulic acid or vitamin E), and once opened, the product should be used quickly, ideally within a few weeks. If it’s in one of those cute dropper bottles, a product labeled as containing 20% L-ascorbic acid likely contains much less than that shortly after opening. 

Irritation is also something to worry about. To remain stable and penetrate into the skin, L-ascorbic acid needs to be formulated at a lower pH of around 3.0-3.5, which means the product is more acidic and therefore potentially more irritating to the skin. If you have sensitive skin, even a few uses may cause burning, redness, and peeling––not what you’re going for in skincare! If you’re among the folks who can tolerate the increased acidity and frequent use, L-ascorbic acid would be a good ingredient for you, but if you have sensitive skin, you might find you only use a product a few times before irritation develops or the product turns yellow. That can be even more frustrating when the product wasn’t cheap. 

So how can you ensure your vitamin C serum or product contains an effective amount of vitamin C that won’t break down in the bottle right after you open it? Some amount of oxidation is normal in every product, but you want one that has been formulated to remain stable during the life of the product. Ideally, the product will have gone through stability testing and maintains the majority of its active vitamin C throughout its shelf life, like Emdash’s Vivid Protect Antioxidant Serum. Ingredient stability testing (or assay testing) is a procedure where a product is exposed to heat and light, mimicking an environment like your bathroom, and then tested at specific intervals to check for ingredient concentrations. Only with this type of testing can we be truly confident that key ingredients remain active in efficacious concentrations over time.  

The form of vitamin C used in the product is also important. L-ascorbic acid is the active form, but can also be finicky and unstable. Other forms of vitamin C are magnesium ascorbyl phosphate or sodium ascorbyl phosphate, which are water soluble and can be formulated at a higher pH for less potential irritation but may not be absorbed as well. Tetrahexyldecyl ascorbate, also known by the trade name BV-OSC, is an oil soluble form of vitamin C. It is more stable because it doesn’t react with water and only converts to the active L-ascorbic form once it reaches the skin. It also releases more slowly, and thus is potentially less irritating. And, the formula doesn’t have to be as acidic to keep the vitamin C stable and active. It’s been shown to better penetrate the skin than ascorbic acid (up to 3 times more!) so you can use a lower concentration daily and get the same benefits without irritation. Some studies even show it can penetrate to the second layer of skin, the dermis, to deliver even more benefits.  

So what percentage should you look for?

As discussed, higher percentages of L-ascorbic acid can be irritating with frequent use. For L-ascorbic acid, percentages of 8-20% are common, but remember that the actual level is unlikely to stay that high with time. For BV-OSC, because of its better penetration, lower levels may be just as effective, and you’ll be able to use it daily without worrying about irritation. In fact, products with concentrations over 3% BV-OSC are considered quasi-drugs in Japan and Korea. Luckily, studies show that even a little goes a long way: a concentration of 0.1% in cells was shown to increase collagen synthesis and reduced melanin (pigment) synthesis, and 3% reduced skin pigmentation from UV exposure. You’ll get more benefit from a gentle, non-irritating product that you can use daily without worrying about breakdown or irritation.  

What other ingredients should you look for? 

Vitamin C is a powerhouse, but some ingredients may work synergistically to help its effectiveness. One such ingredient is ferulic acid, which has been shown to double the photoprotective effect of vitamin C, and provides additional stability to the formula. Vitamin E, or tocopherol, has also been shown in studies to greatly increase vitamin C’s protective actions at the cellular level.  

What else should you look for? 

An effective antioxidant serum will also contain other antioxidants like ferulic acid and Vitamin E to provide more complete protection. Additionally, always look for airless packaging that is opaque. Opaque containers will protect your product from light and airless containers will protect your product from the air. If you do not use an airless container, oxygen will degrade your antioxidants every time the bottle is opened. This means the popular dropper bottles that are found all over beauty counters may not be the best packaging for protecting the fragile ingredients within. 

Once you’ve chosen your product, make sure to keep the bottle in a cool, dark environment (especially if the container is not opaque) to help keep the product and vitamin C levels stable and active. 

How should you incorporate vitamin C into your routine? 

Vitamin C’s antioxidant properties make it an ideal product to use as part of a daily skin defense routine. Ideally, apply it as a serum before heavier moisturizers, and always follow it with a broad-spectrum sunscreen. If you’re developing irritation, reduce the number of days you apply it. If you have sensitive skin, consider a serum with a lower percentage or better yet, a more gentle form of vitamin C so you’ll be able to reap the benefits of more regular use. There are some studies that also suggest vitamin C combined with a retinol at night may help support nighttime skin repair. Ideally, the product you choose will be one you can use daily to help keep your skin glowing and healthy. 

The Emdash Vivid Protect Antioxidant Serum and the Emdash Bright-CE Eye Serum were formulated with tetrahexyldecyl ascorbate and lots of skin barrier supporting ingredients like ferulic acid, vitamin E, ceramides, and peptides. They are formulated, tested, and packaged for maximum vitamin C efficacy and stability.

Disclaimer: As with all our posts, this blog is meant to be for informational and educational purposes, and is not medical advice. When in doubt, please ask your physician. 

Teresa Fu, M.D.

Dr. Teresa Fu is a board certified dermatologist and mother of two. She graduated from Stanford Medical School and practices in the San Francisco Bay Area.