You are in for a real treat today! One of my esteemed coresidents Dr. Kumar Sukhdeo (bio below) gave an excellent talk to our entire dermatology department about the science behind Vitamin C. It was such a good talk that I asked him afterwards to do a guest post here to share with all of you what he found. These are my favorite type of blogposts, because they combine science with skincare, and help you as a consumer figure out what’s actually worth spending money on and what’s a waste. Please leave questions below!
Here we go!
Vitamin C: the devil is in the details!
Vitamin C has been touted as the ultimate natural and organic anti-aging ingredient, but information about vitamin C in topical products is confusing and often inaccurate. Here, I discuss some of the science, challenges, benefits, and recommendations for including vitamin C in your skin care regimen.
Vitamin C Chemistry
First, let’s take a walk down memory lane to revisit some chemistry. Vitamin C, more specifically referred to as ascorbic acid*, is part of a family of molecules known as antioxidants. What does this mean, exactly? To review the chemistry briefly, antioxidants function by donating electrons (negative charges) to other molecules. In doing so the recipient molecule is reduced while the antioxidant is itself oxidized. This is useful in situations when important molecules, such as DNA and proteins (e.g. collagen), are protected from damage through radical oxygen species created by UV exposure, cigarette smoke, pollutants, and others. One way to think of it is that ascorbic acid neutralizes the damage created by the radical oxygen species that carry an unpaired electron. Oxidized ascorbic acid becomes dehydroascorbic acid, which is then further oxidized into additional byproducts. In theory then, topical vitamin C should be beneficial in protecting collagen in your skin from breaking down, which would keep your skin looking more full and youthful. However, research shows that vitamin C may also work on cells in a number of other ways in addition to its antioxidant function.
Ascorbic Acid in Collagen Production
Ascorbic acid gets its name from the Latin “ascorbus” meaning “no scurvy.” Scurvy manifests in many ways including poor wound healing, which was well known to sailors making long voyages without citrus products. Later, scientists discovered that ascorbic acid is essential for cells to produce a finished collagen filament that helps give skin its strength and elasticity.
Several research groups have looked at the question of whether topical applications of ascorbic acid had any benefit in the skin for collagen production. In both petri dishes and in people, applications of ascorbic acid were able to stimulate production of more collagen. Surprisingly, the cells that make collagen grew faster in response to ascorbic acid. In theory, more collagen producing cells might make more collagen for the skin.
Ascorbic Acid in Repairing Sun Damage
Studies of people who applied ascorbic acid with concentration between 3% and 10% (concentrations above 20% actually inhibited absorption) showed a statistically significant reduction in fine lines and wrinkles. These reports are often cited as evidence to support using topical vitamin C in skin care products.
However, it is worth noting that many of these studies used 1) freshly prepared ascorbic acid, often kept in the controlled environment of a laboratory, 2) small numbers of patients with photodamaged (sun damaged) skin (not normal, undamaged skin), 3) subjective scoring criteria (think judges for gymnastics), and 4) observational studies. In reviewing these studies, the benefits were usually very modest, and there was often great benefit from just using the moisturizer cream alone. Therefore, like a delicious orange citrus margarita, much of the science behind ascorbic acid should be taken with a grain of salt!
Vitamin C in Reducing Pigmentation in the Skin
Ascorbic acid has also been evaluated to fade brown spots in the skin. Most skin pigment comes in the form of melanin, a brownish molecule responsible for skin color. On the molecular level, ascorbic acid is able to reduce the visibility of pigment in two ways. First, ascorbic acid inhibits the enzyme (tyrosinase) responsible for making melanin. Secondly, ascorbic acid donates electrons to brown melanin, which becomes a colorless form (see antioxidant function described above). Some studies have shown benefit of topical ascorbic acid in decreasing visibility of brown spots on the face and body. Thus, topical vitamin C may play a role in diminishing age spots and other skin blemishes that surface with age.
Challenges of Vitamin C Getting Into the Skin
In an ideal world, we’d be able to put some vitamin C onto our skin or eat enough vitamin C in our diets and reap all the benefits I just wrote about, right? Well, as we will see, it’s not so simple!
The Skin: a Major Barrier for Entry
The biggest obstacle for ascorbic acid is actually getting into the skin. Melanocyte cells (produce melanin) and fibroblast cells (produce collagen) live below the outermost layer of skin known as the stratum corneum. This is a specialized layer of the epidermis that by design prevents too much water from coming in and too much water from getting out. Herein lies the problem for vitamin C. As a water-soluble vitamin, it must be dissolved in a water (aqueous) base. As such, much of the content in water-based creams are blocked from entering the skin. Still, the absorption of ascorbic acid can be enhanced through pre-treating the skin with laser, chemical, or mechanical (abrasive) means. Complicating matters further is that ascorbic acid is most effective as an antioxidant at an acidity level equivalent to lemon juice (pH <4.0); this can be quite irritating to the skin. To make products more useable for consumers, some manufacturers decrease acidity although this ultimately reduces efficacy too.
Ascorbic acid is most stable in a powder form, but begins to degrade once dissolved in water. Studies have shown that within a month or two at room temperature, more than half the product is lost! The decay of ascorbic acid is further accelerated by heat, higher pH (less acidity), the presence of certain metals (especially copper and iron), and exposure to oxygen in the air.
Ascorbic Acid Derivatives Lack Stability and Efficacy
Cosmeceutical companies have been trying to circumvent the above listed issues by introducing several derivatives. Simply put, they come in two major categories: salt-based and non-salt-based derivatives. The former group includes sodium ascrobyl phosphate (SAP) and magnesium ascorbyl phosphate (MAP). Like regular vitamin C, these derivatives are water-soluble. In contrast, SAP and MAP exist as pro-drugs that must be enzymatically converted in the skin to ascorbic acid in order to have an effect. The evidence that this actually happens on a meaningful level in people is not very clear. These molecules have a harder time getting into the skin than ascorbic acid. Moreover, these studies testing SAP and MAP in the skin are less numerous and not as comprehensive as those for ascorbic acid, so its hard to say if they work as well as ascorbic acid.
The non-salt derivatives, such as ascorbyl palmitate (AA-PAL), are found in many products branded as “vitamin C” but don’t fare much better. These derivatives tend to be lipid-soluble rather than water soluble, so they must be delivered in an emulsion (a mix of oil and water akin to mayonnaise). There is limited data showing they are absorbed past the stratum corneum and may be even more unstable than ascorbic acid. Furthermore, the evidence that non-salt derivatives work to increase collagen, prevent sun damage, and decrease melanin is harder to find.
Given the significant modification of derivatives from the original version, it’s hard to call these molecules equivalent to ascorbic acid. If the supplement industry were regulated like the pharmaceutical industry, SAP, MAP, and AA-PAL, among others, would probably be given a different name and not be allow to be marketed as “vitamin C.”
So, is it worth it?
In a nutshell, the data behind vitamin C’s anti-aging benefits is suggestive but not conclusive, and the experiments used ideal conditions that we may not be able to realistically replicate in real life.
It is harder to tell if the product on your shelf can achieve the same effect as those shown in experiments. That being said, it is worth your time to read the labels and know what you’re buying – the details behind the product and how it’s made do matter!
Unfortunately, there are no consumer agencies that test the stability of ascorbic acid and its derivatives under real-world conditions. To extrapolate from the studies I reviewed, freshly prepared ascorbic acid keeps its integrity roughly as long as an orange in your kitchen (half-life of ~3-4 weeks). If ascorbic acid is kept in a jar (repeated openings to room air with oxygen) and on a bathroom counter (exposed to light; heated with each hot shower) then a consumer might be inadvertently destroying the vitamin C inside!
If you’re concerned about the stability of your product, I’d recommend wrapping any glass bottle in aluminum foil, storing it in the fridge, and limiting the amount of time you keep the lid open.
Given the quick breakdown of vitamin C, it would be worth considering the addition of expiration dates. Could you imagine the sale of eggs or milk without this label?! By the time it is purchased, who knows how long it took to get there, how long it sat on the shelf, and what kind of heat/light conditions it was exposed to during shipment! For this reason, and the evidence cited above, I am cautious about recommending these products and make sure to inform my patients about what they are getting. In my research, there were several formulations of ascorbic acid that were at least prepared under more ideal conditions. These include SkinCeuticals C E Ferulic, SkinCeuticals Phloretin CF, and Cosmetic Skin Solutions C+E sera as well as La Roche Posay Active C10 serum.
I hope this article will help arm you with the information to make informed choices about what you buy for your skin and how to use them to achieve the greatest benefit!
Products mentioned in this post:
* Natural vitamin C (ascorbic acid) exists in two forms that are mirror images of each other (think right hand and left hand): L-ascorbic acid and D-ascorbic acid. Only L-ascorbic acid is biologically active whereas D-ascorbic acid does nothing in the skin. In this article, Vitamin C and ascorbic acid are used interchangeably, and refer to L-ascorbic acid.
Stamford et al. (2012) Journal of Cosmetic Dermatology – Stability, transdermal penetration, and cutaneous effects of ascorbic acid and its derivatives
MyAwesomeBeauty.com – Ultimate Guide to Vitamin C Serums
Oregon State Micronutrient Information Center – Vitamin C and Skin Health
Kumar Sukhdeo MD, PhD is a resident physician-scientist at the Ronald O. Perelman New York University Department of Dermatology. His interests are in evidence-based dermatology, stem cell biology, and hair/nail disorders. All opinions expressed in this article are his own. Hear more from Dr. Sukhdeo via Twitter (@DrKumarSukhdeo). Feel free to post your questions below!