Vitamin C, aka, Ascorbic Acid, is an essential nutrient required by the human body and obtained through the foods we eat. Vitamin C is absolutely required for the synthesis of the mature, and functional, form of collagen, the most abundant structural protein in the human body. Collagen comprises one-third of the total protein in the body, accounts for three-quarters of the dry weight of skin, and is the most prevalent component of the extracellular matrix (ECM).  As you can see, the production of collagen is critical for life to exist. During the synthesis of collagen, two enzymes, called hydroxylases, carry out the task of modifying a couple of the amino acids found in collagen, and this modification stabilizes the collagen protein and gives it structural strength. These two enzymes cannot function without Vitamin C acting s a “cofactor”.

If vitamin C is absent, the mature and strong form of collagen cannot be made and becomes unstable and unable to function to strengthen the connective tissues of your body. A cartoon showing the collagen structure is shown here. Note that mature collagen exists as a triple helix (3 collagen proteins wrapped around each other). This helix then combines with others to form the strong collagen fiber found in all connective tissue. Imagine what would happen if the collagen proteins couldn’t form a triple helix. If this happened they couldn’t form into a collagen fiber, but instead would be broken down and destroyed. Without Vitamin C, no helix structure nor collagen fibers could form.

Collagen is required for the efficient healing of bone, tendons and ligaments? People who are deficient in Vitamin C experience poor wound healing, increased risk of infection, gum disease, changes to hair, and bleeding from the skin. Vitamin C deficiency also results in tiredness, weakness, and a loss of immunity.  This disease is probably well known to you from history books. It is called Scurvy. As scurvy worsens opens sores appear on the skin, caused by the skin rupturing without the support of collagen. These open wounds do not heal and because of poor immunity, they become infected leading to death from infection or bleeding. Back in the 1600s and even earlier, sailors at sea for many months developed Scurvy and many died before returning home. In 1747 a British doctor discovered that if sailors were given citrus juice (usually lemon juice) during their voyage they did not develop scurvy. That prompted the British government to issue lemon juice to sailors on all their ships. We now know that lemon juice contains vitamin C, but it wasn’t until the twentieth century that vitamin C was isolated and its structure determined.

As we all know, collagen is an important structure component of skin and is found in the dermis. Without collagen the skin develops wrinkles, loses strength and elasticity, sags and becomes thin. So if we think about the role of vitamin C in maintaining a healthy, youthful skin we can now appreciate its importance. More recent studies have shown that not only is vitamin C a required cofactor for the two enzymes that are responsible for the final steps of collagen synthesis, but we now know that Vitamin C can also directly activate the gene for collagen, thereby increasing the amount made by the fibroblasts in the dermis. And finally, vitamin C is an antioxidant and in this role, vitamin C blocks the activity of free radicals thereby protecting the skin from the damaging effects of sun exposure. And many scientific studies have suggested that vitamin C may be able to  prevent various cancers, including skin cancer.

It’s clear that vitamin C is a necessary nutritional supplement and it seems like it should be a great ingredient to put into any skin care product. And while that’s true, for  vitamin C is to provide any benefits to the skin when applied topically, it has to get into the skin and this means getting past the skin’s protective surface barrier (the stratum corneum). This turns out to be somewhat of a challenge. 

Vitamin C is water soluble (polar) and since the skin’s surface barrier is mostly made up of lipids (oil like compounds that are non-polar), as a water-soluble vitamin, it can’t penetrate a lipid layer (remember water and oil repel each other).  The only way to get vitamin C across the stratum corneum is to make it less water soluble (less polar) and this can only occur when vitamin is no longer a charged molecule.   If the pH of the lotion that vitamin C is formulated in is very acidic, that is around pH 3.5 or less, the charge on vitamin C is eliminated and some of it can now pass through the surface layer. This is a challenging formulation task, and, as you might guess, a topical lotion with a very acidic pH can be irritating to some consumers. The other way to get vitamin C into the skin is to convert it to a more “oil-like” , less polar molecule and a great deal of effort has been put into the development of “lipid-like”/non polar ascorbic acid derivatives for the purpose of topical application. You’re probably familiar with many of these forms of vitamin C since they are found in many skin care products. These derivatives including Ascorbyl Palmitate, Sodium  Ascorbyl phosphate, Ascorbyl Glucoside, and Tetrahexyldecyl Ascorbate (THDA) can pass through skin’s surface barrier more easily than vitamin C. However, because they are derivatives of vitamin C, once in the skin they need to be converted to vitamin C to be effective. 

If a formulation containing  Vitamin C in it is going to provide any benefits when applied topically it needs to contain a concentration of Vitamin C that has been shown in scientific studies to be effective. So what is this concentration? The amount needed to be effective varies depending on the type of vitamin C put in the formulation. For example, acidic formulations (pH <4) that contain pure vitamin C (not a derivative) usually contain 10-20% vitamin C. This high concentration is needed to obtain any benefits. On the other hand, formulations that contain Tetrahexyldecyl Ascorbate (THDA) have been shown to be effective if only 3% THDA is used. 

The last important requirement for an effective vitamin C product is that the vitamin C put into the formulation needs to be stable. Interestingly, if you dissolve vitamin C in water and wait for less than an hour, you’ll see that the water has turned brown or black. This is because the vitamin C has been oxidized and degraded. It is no longer effective. So any lotion or cream that contains vitamin C will likely turn yellow or brown in just a couple of months, because the water in the formulation is breaking down vitamin C. Some of the vitamin C derivatives are more stable in formulations that vitamin C, but even these will degrade over time. The best formulations for keeping vitamin C stable are those formulations that contain NO water. DermaMedics Restorative Serum is a good example. This vitamin C product is a silicone based serum that contains no water, and with no water, there is no oxidation of vitamin C. 

In conclusion:

  1. Vitamin C is absolutely essential for maintain a healthy and youthful skin
  2. Topical products containing vitamin C must meet the following 3 criteria:
    1. The form of vitamin C used must be able to penetrate across the skin’s surface.
    2. The amount of vitamin C in the formulation must be sufficient to provide significant skin benefits. Putting an amount of vitamin C into a formulation that is knowingly too little to provide any benefits at all, simply for the purpose of marketing claims is referred to as “fairy dusting” 
    3. The formulation needs to be designed to make sure the vitamin C in the product is stable and not easily oxidized.