Douglas Q. Kitt, BS and Jay P. Kitt, PhD, MS
Vitamin C has many benefits in skincare including providing antioxidant protection, enhancing collagen production, promoting collagen crosslinking, and reducing hyperpigmentation. Because of these many benefits, Vitamin C is offered in a plethora of skincare products and is the number one dermatologist-recommended ingredient.
What many people don’t know is that Vitamin C exists in two natural forms: L-Ascorbic Acid and L-Dehydroascorbic Acid (DHAA). L-ascorbic acid is the form predominantly used in skincare. Unfortunately, the benefits of DHAA are often overlooked, or worse yet, disacknowledged. This is largely due to an abundance of misinformation which continues to find its way into skincare communities online and is often spread by manufacturers looking to keep up sales of their ascorbic acid formulations.
In this post, we aim to address this misinformation through an in-depth look into the science of both L-ascorbic acid and DHAA. If you are interested in enhancing the health of your skin, read ahead and discover the beautiful science of Vitamin C absorption from the moment you apply it until it reaches the intracellular compartments where the work of this amazing molecule begins.
The vitamin C you know: L-ascorbic acid
Most people are familiar with the benefits of pure ascorbic acid in skincare, however little attention is paid to the challenges of getting ascorbic acid from the surface of the skin into the cell. Ascorbic acid is very water-soluble and ionized at neutral pH, these two properties prevent it from easily passing through the outer layer of skin known as the stratum corneum. This is because the stratum corneum is made up of dead skin cells and when the cells die, they become dehydrated leaving mostly hydrophobic lipids behind. These lipids protect our living skin acting as a hydrophobic (water-repelling) barrier between the living cells and the outside world. This same property is what makes the stratum corneum a barrier to ascorbic acid absorption. Compounds which are easily dissolved in water and especially those which have a charge (ions) are repelled by this obstacle and only small amounts get through.
To overcome this, most Vitamin C serums contain high concentrations of ascorbic acid (10 – 20% or even higher!) and are formulated at acidic pH to keep the ascorbic acid in its neutral (non-ionic) form. These measures increase the absorption of vitamin C, however, they also lead to some of the more common complaints about ascorbic acid products such as burning and irritation. Worse yet, even these somewhat extreme measures don’t solve the absorption problem. Studies have shown that ascorbic acid, even under these harsh conditions, is still very slowly absorbed through the stratum corneum. In-fact, less than 2% of the ascorbic acid will end up in your living skin within the first four hours following application!1 Unfortunately, this means that the majority of the ascorbic acid you apply to your skin will never reach the living tissue you want to protect. Don’t go throwing out those expensive serums just yet, though. Even the small dose of vitamin C provided by a typical ascorbic acid serum helps your skin. Topical ascorbic acid provides more vitamin C to the skin than taking a vitamin C tablet and the benefits of topical ascorbic acid to the skin are well-documented.2 However, next time you are considering a vitamin C serum, ask yourself, “Is there something better?”
Dehydroascorbic acid – confusion and clarity
If you’ve heard of DHAA in the skincare community online, it’s likely been in a disparaging light. Words like “degraded,” “spent,” “used-up,” and “unstable” abound on discussion boards, forums, and in Facebook groups when DHAA is mentioned. An important question for the astute reader is, “What is the source of this information?”
The websites of many companies, looking to keep up the sales of their ascorbic acid-based vitamin C serums, are full of such jargon. Some cite research articles in a biased-fashion. Some are uninformed. Often, manufacturers are simply trying to push you to buy their product and mean no harm when they talk about vitamin C degradation; they just want you to feel confident that the product you are buying is stable. No-matter the reason, the unfortunate truth is this: You have been misinformed.
The interplay between ascorbic acid and DHAA, is a beautiful dance between molecules. It is an essential pathway for maintaining vitamin C throughout your body and as you’ll learn below, this chemistry has provided a revolutionary step forward in vitamin C skincare and supplementation.
Deep within your skin, in the living tissue, inside of each cell, ascorbic acid and dehydroascorbic acid are being interconverted every second of every day. When a molecule of ascorbic acid is used to fight off a free-radical or other oxidant, it gives up electrons in a process called oxidation. When this happens, ascorbic acid is turned into DHAA; sadly, many would have you believe that this is where the story ends and that this vitamin C is now “degraded.” We’re here to inform you of the truth: DHAA is not “degraded,” vitamin C, it is only a single step from being recycled back into ascorbic acid via one of many pathways, and in-fact, for some cells and cellular machinery, DHAA is the only form of vitamin C they can import.
Your cells have the incredible ability to recycle DHAA and convert it almost immediately back into ascorbic acid, ready to fight again. This is most frequently accomplished by an enzyme called glutathione dehydroascorbate reductase, although there are at-least five known additional recycling pathways.3 You can think of an enzyme as a small machine used by a cell to produce or alter other molecules and this enzyme’s function is described well by its name. Glutathione dehydroascorbate reductase uses glutathione, which your body can produce, to reduce DHAA, and turn it back into ascorbic acid, a molecule that your body can’t produce. In-effect, you trade a non-essential nutrient (glutathione) to retain an essential one (ascorbic acid). To maintain this ability, your body can also very quickly recycle the glutathione.3,4 Our bodies aren’t wasteful! Additionally, by actively utilizing the vitamin C recycling pathway, you stimulate the cell to increase the production of glutathione and studies show that in a matter of 1-2 days, the overall effect of DHAA conversion to ascorbic acid is an increase in the amount of glutathione in the cell.5 This is analogous to exercising. When you go for a run, you use and strain your muscles which stimulates your body to produce more and stronger muscle fibers. While you might be sore for a day, the net result will be a stronger and healthier you!
Dehydroascorbic acid in skincare – better than ascorbic acid?
“If you are using a pure ascorbic acid serum, you are missing out on the many benefits of the other form vitamin C, DHAA.”
Now that you know that DHAA is quickly and readily converted to ascorbic acid, let us step back to the previous discussion of the stratum corneum and ascorbic acid and consider the absorption of DHAA.
DHAA is less water soluble than ascorbic acid, and more importantly is not ionized at the normal pH of your skin. These two properties lead to dramatic differences in the absorption of DHAA through the stratum corneum. DHAA crosses this barrier 1200% faster and to levels 2 to 20 times higher than ascorbic acid.2 Leading to greater accumulation in the living tissue. This is great news, but, the stratum corneum is only the first barrier to vitamin C absorption.
Once vitamin C molecules reach the living tissue, they diffuse through the extracellular fluid to the surface of the living cells. Here they reach the second barrier, the cell membrane. This membrane is made of the same lipids that make up a large part of the stratum corneum, but in living cells, the membrane is hydrated and defect-free forming an even more selective barrier, protecting the interior components of the cell. Neither ascorbic acid or DHAA can cross this barrier without help. The helpers, which move molecules across the membrane and into the cell are called transporters and vitamin C is moved across the membrane by two types of transporters: SVCT and GLUT. SVCT transporters carry mostly ascorbate (charged ascorbic acid) and some ascorbic acid, while GLUT transporters carry dehydroascorbic acid.7 Skin cells have both types of transporter and can absorb both ascorbate and DHAA. Here again, however, charge becomes a factor. Cells tightly regulate the number of charged molecules inside the cell. In order for the cell to “allow” ascorbate to enter, the cell must get rid of other charged molecules. This means that SVCT transporters must combine a pump for moving ions out of the cell at the same time ascorbic acid is transported in. Pumps require energy and energy takes time to produce so SVCT transporters are comparatively slow. Since DHAA is not charged, the GLUT transporter which allows DHAA into the cell doesn’t require this pump and DHAA is passively transported (requiring no cellular energy). Because of this, DHAA is absorbed much more rapidly. Studies have shown that DHAA is absorbed by the cell at a rate 10-20 times faster than ascorbic acid and again, to levels 2-20 times higher.8,14 Once in the cell, DHAA is rapidly converted into ascorbic acid and acts as a protective antioxidant. Thus, by using DHAA instead of ascorbic acid in your skincare formulation, your cells can acquire more vitamin C, and do so much more rapidly than if you use a pure ascorbic acid formula.
If your only interest is the Vitamin C as an antioxidant, you’ve reached the end of the story. However, vitamin C has more roles in skincare than simply antioxidant protection, and DHAA plays an equally important role in that process: collagen production.
DHAA and healthy collagen
Within the cells are small “factories” called organelles which produce many of the proteins and molecules cells use to function. The endoplasmic reticulum is the organelle where collagen is produced in your skin. To keep the skin flexible and resilient, collagen must be strong and elastic which the cell accomplishes by gluing, or crosslinking, collagen fibers together, a process which is carried out in the endoplasmic reticulum and requires vitamin C.9 Interestingly, the endoplasmic reticulum is known to have no, or at least very few, SVCT transporters, and recent research suggests that not only is ascorbic acid transport into the endoplasmic reticulum extremely limited, but that DHAA is the preferred form of vitamin C transported into this organelle.10,11 Vitamin C is almost exclusively brought into the endoplasmic reticulum as DHAA and then converted into ascorbic acid for use in collagen crosslinking. As such, the use of DHAA in vitamin C skincare products may well provide a more efficient pathway to promote production of healthy collagen.
An overview – misinformation vs. truth.
We hope you’ve enjoyed this discussion of the science of vitamin C in the skin. To briefly recap, we’ve provided a simple Q & A summary, below:
Q: Is DHAA is “degraded, spent, used-up” Vitamin C?
A: No. DHAA is an active form of vitamin C that your body absorbs readily and recycles regularly. On average 10 – 20% of the vitamin C people get from food is DHAA; people who eat lots of fresh fruit and vegetables consume even more; it is absorbed from the gut, converted to ascorbic acid, and peak in the bloodstream about 2 times faster than ascorbic acid;10 scientific studies have demonstrated it can substitute completely for ascorbic acid in the diet.12
Q: Is DHAA “pro-oxidant?”
A: No. The pro-oxidant effect of vitamin C results from oxidation of ascorbic acid by iron and oxygen. This process results in the formation of hydrogen peroxide.13 DHAA is already oxidized, and does not undergo the same reaction. Ascorbic acid is the form of vitamin C with pro-oxidant capacity, albeit indirect.
Q: Is DHAA “unstable?”
A: Yes, and no.
- In water at neutral pH and room temperature, its half-life is on the order of minutes. For example, in phosphate buffered saline (similar to serum) at body temperature, the half-life is 50 min.15
- In glycerin containing a mild acid (like ascorbic acid) at room temperature, its half-life is on the order of months. At freezer temperature, we have not been able to detect deterioration over many years.
- In your bloodstream and tissues, DHAA is rapidly recycled; only a tiny fraction is lost by conversion to DKG. In a person who has no dietary intake of vitamin C, the body’s stores decrease slowly, at rate of about 3% each day, even though ascorbic acid is near continuously utilized.15 This is due to interconversion between ascorbic acid and DHAA.
Q: Does DHAA “deplete” glutathione?
A: It does not. During the recycling process, DHAA oxidizes glutathione, but that glutathione is also rapidly recycled. Additionally, increased use of the glutathione recycling pathway stimulates the cell increase the glutathione production; in a matter of 1-2 days, the net effect is an increase in the amount of glutathione in the cell.
Want to learn more?
If you’d like to read more about these topics, visit our science page or click the links to the literature sources below!
- https://www.liebertpub.com/doi/abs/10.1089/ars.2019.7912?journalCode=ars (We apologize we could not find a full-text link for this article!)