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Vitamin C in skin care is a well researched and proven active ingredient.
It is widely recognised and used for its strong anti-ageing benefits.
Vitamin C, in the form of L-Ascorbic Acid, has a strong pedigree and science to back up many of the claims made for it.
Vitamin C can protect against and help repair UV-induced cell damage, stimulate collagen production, reduce wrinkle depth and lower melanin production. And that is why it is a skin care hero ingredient that deserves a place in most skin care routines.
But not all types of Vitamin C in skin care are equally active.
If you want to get the most out of using Vitamin C in your skin care routine, it pays to spend some time getting to know the different forms of Vitamin C and what they do. That way, you can pick the one that best suits your skin type and targets your skin concerns.
As an antioxidant, Vitamin C protects skin from oxidative stress when exposed to UV light by neutralising free radicals and preventing them from doing cellular damage, including to collagen. Oxidative stress leads to inflammation and premature skin ageing, including possible melanoma formation.
Given UVA rays penetrate significantly deeper into the skin than UVB rays, they can be highly damaging to your skin. Many dermatologists recommend applying topical antioxidants, such as Vitamin C, to your skin every day, and ideally twice a day, however this is not necessarily possible when you have other goodies in your routine. This approach helps to prevent photo-ageing, as sunscreens only block 55% of the free radicals produced by UV exposure. It has been found that applying a sunscreen after using a topical Vitamin C increases the protection provided by the sunscreen. Yet when applied at night, it helps to counteract damage caused by UV exposure during the day, given that free radical activity has been found to continue to occur at night.
Despite Vitamin C providing great antioxidant protection for skin, it is best paired with other antioxidants, which work to significantly increase its protective effect. Some leading brands even have patents protecting their formulations.
L-Ascorbic Acid is the chemically active form of Vitamin C and the form that first appeared in skin care products. It is easily absorbed by the skin, with percutaneous absorption at 15% being higher than that for Ascorbate derivatives. Studies show it delivers antioxidant protection, brightening effects and collagen stimulation. L-Ascorbic Acid is best paired with other antioxidants to multiply its beneficial effects and to provide sustained activity through the various stages of binding to free molecules of oxygen.
The type of Vitamin C used in skin care formulations really matters, especially for L-Ascorbic Acid, which requires the right concentration, the right pH, the right stabilisation and the right delivery mechanism. L-Ascorbic Acid works by binding to free radicals of oxygen, and in doing this prevents these from binding to your skin cells. Unfortunately, though, oxidisation can start to occur soon after the product is manufactured, as seen when the serum turns light orange, dark orange and then brown.
Once an L-Ascorbic Acid serum has changed in colour, it has not only started to lose its functional benefits, it can be damaging to the skin.
SR Pinnell et al established that that L-Ascorbic Acid is maximally effective at a concentration of 20%, so levels higher than this will more likely irritate your skin and deliver less benefit. It also needs a pH of less than 3.5. At the right pH, L-Ascorbic Acid is able to penetrate the epidermis, however given it is a water-soluble molecule, its transdermal absorption has been found to be low. Brands claiming their formulations have 30% L-Ascorbic Acid are doing this for marketing purposes and you should be wary of any claims they make for their product.
L-Ascorbic Acid is difficult to formulate due to its sensitivity to air and light, and its fleeting maximum effectiveness once bottled. Unless the manufacturer can manage all these elements correctly, you could be wasting your money. What is worse, you could be using an L-Ascorbic Acid product that has oxidised and is now harmful to your skin.
Beware when your L-Ascorbic Acid starts to turn coloured. Some manufacturers claim that a coloured L-Ascorbic Acid is fine to use. So at what point do you throw it out? Do you wait until it is brown, when it is orange or as soon as it turns a little yellow? It seems this a point of strong debate among the brands, depending on their own formulation approach, and one that really needs greater scientifically based information from the manufacturers. The lack of clear guidance to consumers from skin care manufacturers and the brands is concerning.
Storing your product in the refrigerator can slow the oxidisation process down. In serums, this can, however cause some crystallisation around the top of your bottle, but this is not something to worry about.
To prevent oxidisation, manufacturers have developed water-free formulations that have the consistency of dry oils, and there has been a huge growth in these. Another benefit is that they penetrate the skin’s lipid barrier more easily. Many people prefer the stability, consistency and ease of application of these, given they do not absorb as quickly, but the drawback is they contain ingredients such as Ethoxydiglycol, Propylene Glycol, Butylene Glycol and Phenoxyethanol in high amounts, rather than very low amounts.
Additionally, manufacturers have created L-Ascorbic Acid in oil formulations, however these can be difficult to layer and are not an ideal choice for many.
Today there are now a number of Vitamin C derivatives that are stabilised, including Ascorbyl Glucoside, Ascorbyl Palmitate, Magnesium Ascorbyl Phosphate and Sodium Ascorbyl Phosphate, which are often used in concentrations of 0.2% to 15%. These other forms still need to be converted to the pure form of Vitamin C, L-Ascorbic Acid, for them to be available to the skin for uptake. Conversion is not perfect and therefore little L-Ascorbic Acid may be available to the skin for use.
Some forms of Vitamin C derivatives are proven and others are promising, but may not yet have shown the same clinical benefits of L-Ascorbic Acid, specifically in stimulating collagen and reducing wrinkle depth.
Tetrahexyldecyl Ascorbate is the most interesting new kid on the block. There has been a lot of hype around it, but research is limited to that undertaken by the manufacturer. It is claimed that is as effective as L-Ascorbic Acid but without the irritation, not just as an antioxidant, but also as a collagen stimulator and tyrosinase inhibitor.
Most other Vitamin C derivatives remain on the surface of the skin where they guard against oxidative damage and may help brighten skin, but do not play a major role in stimulating collagen.
Choosing the best form of Vitamin C really depends on your skin type and your skin concerns. For example, Sodium Ascorbyl Phosphate has been found to work well for brightening and for acne.
While L-Ascorbic Acid is the best bet in skin care, given its proven effectiveness, it does not suit everyone. Remember, if you do chose an L-Ascorbic Acid formulation, ensure you are buying a reputable brand. The company manufacturing it needs to have the expertise to stabilise the formulation and facilitate its penetration so that it can activate fibroblasts in the dermis. The leading brand has a patent on its antioxidant blend and pH, which has forced some competitor dupes to go too high or too low in their pH.
The way a product has been formulated is just as important as the amount of L-Ascorbic Acid used. This form of Vitamin C is a prima donna ingredient that is extremely difficult to work with. L-Ascorbic Acid needs to be stabilised and needs to be in the right concentration, considered to be 10-20%. Given the potential for harm from oxidisation, as seen when a clear serum changes colour, we think it is best to stick with the best brands.
However the percentage of L-Ascorbic Acid in one skin care product cannot be compared directly with the percentage of a Vitamin C derivative used in another product.
Trying to determine the best form of Vitamin C to use is no easy feat. Despite the evidence backing up the benefits of L-Ascorbic Acid, there are some people who are irritated by it or do not respond to it and need to use a Vitamin C derivative.
There are claims and counter-claims among leading cosmetic and pharmaceutical houses as to whose version of Vitamin C performs better, and this is an argument that will continue to play out. Even the experts do not appear to have a consistent position. Those producing L-Ascorbic Acid forms typically claim that this is the only form of Vitamin C your skin will recognise and utilise. On the other hand, those making lipid-soluble forms claim that L-Ascorbic Acid cannot penetrate the skin at the same level and therefore does not have the ability to reverse damage and regenerate the skin.
This makes choosing the right Vitamin C very tricky.
L-Ascorbic Acid has the strongest science behind it, and it is the most bioavailable to skin, but a product that has started to oxidise will have less potency and benefit than a stabilised derivative. Many people simply shop by looking at the percentage of Vitamin C in relation to L-Ascorbic Acid, but products using different forms of Vitamin C cannot be measured directly in this way.
One study of Vitamin C formulations found L-Ascorbic Acid has the best antioxidant effect when compared with Vitamin C derivatives. That said, Vitamin C derivatives may have other benefits that also prevent early skin ageing.
A dietary study reported in the Journal of the American Dietetic Association, July 1994, found that copper acts as an oxidant to increase the rate of breakdown of L-Ascorbic Acid to the inactive form, Diketogulonic Acid. So just another thing to consider when choosing your preferred type of topical Vitamin C.
Research indicates that Magnesium Ascorbyl Phosphate appears to be most stable and most effective at scavenging free radicals, improving the appearance of melasma and senile freckles, and stimulating collagen at 10%. Another benefit is that it improves skin hydration.
The skin has enzymes that can convert Vitamin C derivatives, such as Magnesium Acorbyl Phosphate, to Ascorbic Acid, but it does so imperfectly. The amount that gets converted is unknown and varies from person to person.
Sodium Ascorbyl Phosphate at 10% is also equivalent to a much higher level of L-Ascorbic Acid, and it is more bioavailable than Magnesium Ascorbyl Phosphate. The maximal concentration, however, for “percutaneous absorption” of Sodium Ascorbyl Phosphate is 20%. Additionally, it has the benefit of a pH of 6.5, which makes it helpful if you are layering it with peptides or growth factors.
Woolery-Lloyd, Baumann and Ikeno, Journal of Cosmetic Dermatology, 2010, found that Sodium Ascorbyl Phosphate at a concentration of 5% improved acne in 76.9% of patients, a considerably higher rate of success, with no side effects, than commonly prescribed treatments: 5% Benzoyl Peroxide, 1% Clindamycin, 0.1% Adapalene. Its effectiveness in treating acne was due to its ability to prevent sebum oxidisation.
Also keep in mind that some other forms of esterified Vitamin C, unlike L-Ascorbic Acid, are also stable at a neutral pH, which makes them more suited to sensitive skin. If formulated in a base of oils or lipids, they penetrate more deeply rather than evaporate quickly when applied in a base of water.
Tetrahexyldecyl Ascorbate is the newest form of Vitamin C used in skin care products. It is fast gaining in popularity as it is highly stable and lipid soluble, allowing it to more easily reach the dermis where it can stimulate collagen production. Manufacturer research shows it can trigger the production of glycosaminoglycans in your skin, naturally occurring compounds that bind and hold on to water. Also in its favour is that it is less irritating, although its potency cannot be measured in the same way as that for L-Ascorbic Acid. It is claimed to be an exceptional tyrosinase inhibitor and therefore particularly helpful in brightening skin. Keep in mind, though, that it is a relatively new ingredient and does not have a body of research behind it.
So, by now you are wondering ‘which Vitamin C is best in skin care?’ It really depends on your skin type and the benefits you are looking for from your Vitamin C. Is it collagen production? Is it antioxidant protection? Is skin pigmentation improvement?
Someone with an impaired skin barrier, such as acne or rosacea, may find L-Ascorbic Acid to be too irritating and actually further worsen their skin, so are better off choosing a Vitamin C derivative that has a neutral pH. On the other hand, someone with photo-aged skin may need the power of an L-Ascorbic Acid. Keep in mind that every skin is individual and will respond in its own way to the different forms of Vitamin C, as well as the product formulation.
Still confused? Refer to our Vitamin C Comparisons table below for some further help on choosing the best Vitamin C for your skin.
| Vitamin C | Converted to Ascorbic Acid | Stability: pH Required | Penetration | Collagen Synthesis | Photo Protection | Brightening | Irritation |
|---|---|---|---|---|---|---|---|
| L-Ascorbic Acid | Very low – pH <3.5 | Solution or micro particles | Yes | Yes | Yes | High | |
| Sodium Ascorbyl Phosphate | No data | Neutral – pH 6.5 | Yes (ex vivo) | Yes (in vitro: less than MAP) | Yes | Yes | Low |
| Magnesium Ascorbyl Phosphate | Yes (in vitro) | Neutral – pH 7 | Yes (ex vivo) | Yes (in vitro) | No data | Yes | Low |
| Ascorbyl Palmitate | No data | Neutral – pH 6.5 | Dependent on formulation | Yes (in vitro) | Yes (animal in vivo) | No data | Low |
| Ascorbyl Glucoside | Yes (in vitro) | Neutral – pH 6.5 | Yes (in vitro) | Yes (in vitro) | Yes (less than SAP) | Yes (in vitro) | Low |
| Ascorbyl Tetraisopalmitate / Tetrahexydecyl Acorbate | Yes (in vitro) | Low – pH < 5 | High (84%) | Yes (in vitro) | Yes (in vitro) | Possibly | Low |