Vitamin C Serum Reviews
Reviewed by Louise Hidinger, Ph.D.
Vitamin C skin care products are well-known in the world of cosmetics, and have been around for a while, but there have been some advances in their formulation that make this ingredient worth revisiting.
Ascorbic acid occurs naturally in both plants and animals, but humans lack the ability to synthesize it so it must be obtained through our diet. Ascorbic acid is required for numerous biochemical pathways in the human body, including the biosynthesis of collagen, which is an important structural component of connective and epithelial tissue (which includes skin). A deficiency in Vitamin C gives rise to scurvy, a potentially fatal disease if not treated in time.
Ascorbic acid is also an antioxidant. Generally speaking, antioxidants are molecules which are readily oxidized and serve to protect other molecules from oxidation. Within the body’s cells, ascorbic acid serves to keep the metal ions found in the catalytic centres of certain enzymes at the correct oxidation state, thus keeping the enzymes active as catalysts. It also serves to mop up free radicals and thus prevent them from attacking and damaging parts of the cell via oxidative reactions.
There have been numerous studies to show that topical application of Vitamin C is one of the best and easiest ways to boost skin radiance and to improve the appearance of wrinkles. The activity of Vitamin C is thought to work in a number of ways, including:
1) to aid collagen production, thereby helping to maintain skin volume and firmness.
2) to inhibit free radical damage and oxidative stress on skin tissue, due to environmental stressors such as U.V. radiation and pollution.
However, there are serious obstacles to be overcome when trying to formulate Vitamin C into a working cosmetic formulation.
Why Vit C serums are sold in opaque glass bottles
One of the main problems is that an aqueous solution of ascorbic acid oxidizes readily upon contact with air, and becomes dehydroascorbic acid, which is biochemically inactive. This oxidation is further accelerated by the presence of metal ions and light. It is for this reason that Vitamin C serums are almost always packaged in amber or opaque glass containers.
One way to preserve the activity of Vitamin C is to combine it with other antioxidants, the idea being that the presence of other antioxidants will compete for reaction with free radicals. An example of such an antioxidant is Vitamin E (also known as tocopherol).
The other major problem of formulations of Vitamin C is how to get it to penetrate the skin to its site of activity, i.e. within the layers of the epidermis and the dermis where there are skin cells actively dividing. Ascorbic acid is water soluble, and if used in this form, it must be formulated in a water-based composition. The stratum corneum, which is the outermost layer of the epidermis, is composed of mostly keratin and dead skin cells, and it is the main barrier to penetration of water-based solutions.
Cellex-C High Potency Serum is a straightforward formulation of 10% ascorbic acid in water, along with acetyl tyrosine (an amino acid), zinc sulfate, sodium hyaluronate, and bioflavanoids derived from green tea (Camellia sinensis).In order to get the ascorbic acid to penetrate to its site of activity where skin cells are actively dividing, and to do this before the ascorbic acid is oxidized, one has to use a relatively high concentration of ascorbic acid. The alternative is to use a derivative of ascorbic acid that is oil soluble, and can penetrate the outermost layers of skin more readily.
It is packaged in an amber glass bottle with a dropper, and it appears as a pale yellow solution that darkens over time, indicating the oxidation of ascorbic acid. The Cellex-C representative told me that I didn’t have to keep it in the fridge, but I noticed that the solution darkened rapidly, becoming a dark yellow within a month after opening. I am currently on my second bottle and this one I keep in the fridge. About 5 drops is enough for one application; the serum should only be applied once a day, either morning or night. I have been applying it in the morning underneath SPF 30 sunscreen . As it is quite acidic, I felt a light stinging sensation when I first tried it, but this sensation went away after a few days of use. I was told to expect notice changes after about 4 weeks of regular use and this was the case. This serum is really excellent for boosting skin “glow”, but the other major effect is that is has really helped with refining skin texture and minimizing the appearance of pores.
Unlike the Cellex-C serum, which is water-based, the Kellett Topical Vitamin C Ferulic Serum is based on a liquid silicone, cyclomethicone. The form of Vitamin C found in the Kellett serum is tetrahexyldecyl ascorbate, which is an oil-soluble derivative of ascorbic acid. According to the formulators of this serum, tetrahexyldecyl ascorbate penetrates the skin three times higher than ascorbic acid, when both are applied at the same concentration. As tetrahexyldecyl ascorbate is oil-soluble, it can penetrate the skin much more readily than ascorbic acid. The Kellett serum contains additional antioxidants, Vitamin E (tocopherol), green tea extract, and ethylhexyl ferulate (an oil-soluble form of ferulic acid, a plant-derived antioxidant). The combination of antioxidants acts to stabilize each other and thus increase their overall effectiveness, as well as increase the shelf-life and stability of the formulation. Finally, the Kellett serum contains tridecyl salicylate, an oil-soluble derivative of salicylic acid, a chemical exfoliant which serves to further refine skin texture. This serum was developed by Dr. Lisa Kellett, a well-known dermatologist based in Toronto. Along with a cosmetic dermatology practice, she also has her own skin care line.
The Kellett serum is comparable to SkinCeuticals CE + Ferulic serum (see earlier review here). Although the Kellett serum comes with instructions to apply every other night, I decided to follow the same regimen as with the SkinCeuticals serum, i.e. applying in the morning, followed by SPF 30 sunscreen over top, before heading out for the day, the idea being to use the antioxidants in the serum to protect skin against oxidative damage from environmental exposure during the course of the day. However, due to the presence of the salicylate, those with sensitive skin should stick with applying the serum at night, and be sure to wear sunscreen during the day.
Because this is a silicone solution, it is appears as a very thin, oily liquid that absorbs quickly with a very fast dry-down, so you have to spread very quickly before it absorbs. When I first started using this, I used about 5 drops, but found that after about a week of this regimen, I started to break out and I was getting a lot of plugged pores. From long experience, I know that silicone-based formulations don’t work well on my oilier, stress-prone skin type, and so I was not surprised that I had this initial reaction to the Kellett serum. (Besides the breakouts, too much of it makes my skin feel uncomfortable and slightly itchy.) I cut back to 2-3 drops per application, working quickly to apply a very thin film, and that has worked out better for me – no breakouts and far fewer plugged pores. If you have a similar issue with silicone-based formulations, I think the key to this one is to apply very sparingly.
Winner: Kellett Topical Vitamin C Ferulic Serum
The Kellett serum definitely helps to boost radiance and to refine skin texture. Unlike the Cellex-C serum, the Kellett serum is colourless, plus it does not change colour over time, and it does not need to be refrigerated. The Kellett serum has almost no odour at all, a big plus compared to the SkinCeuticals serum, which had a strong, unpleasant odour of amines, similar to uncooked hotdogs. This serum is recommended for its ease of use and its anti-ageing and skin-protective effects.
About the Author Louise Hidinger, Ph.D., is a chemist and founding editor of the beauty blog INGREDIENTS.