The Vitamin C Guide

When internalized, vitamin C is an essential nutrient that our bodies need to form cartilage, tissue, muscle, and blood vessels and an antioxidant that helps our body protect itself from free radical damage from the inside out. When used topically in skin care, derivatives of vitamin C are favorite active ingredients among dermatologists thanks to the myriad proven benefits––brighter, smoother, more even skin with fewer blemishes, black heads, dark spots, and fine lines.

The most common active derivative of vitamin C found in skin care (and generally, the easiest one to spot on an ingredient list) is ascorbic/L-ascorbic acid, which is the most effective at penetrating the skin barrier, though is less stable than other forms. This means that the product can oxidize when exposed to light and air, so the packaging matters––look for dark and/or opaque bottles and application methods that prevent exposure to either.

While most research and product development around vitamin C has been done in the form of L-ascorbic acid, a promising new derivative of vitamin C, tetrahexyldecyl ascorbate (THD), is rising in popularity. Where L-ascorbic is water-soluble and unstable, THD is oil/fat-soluble (and therefore will be found in serums, oils, and creams) and is more stable. It should be noted that there are very few official studies confirming these findings, but those that have surfaced are promising.

Two other forms of vitamin C you’ll find in skin care include sodium ascorbyl phosphate and magnesium ascorbyl phosphate (which is water-soluble). These are more stable but less active forms of vitamin C which while may not penetrate as well as L-ascorbic acid, those with sensitive skins may prefer these forms as they are less irritating.

When choosing a vitamin C-powered topical product, first you need to understand your skin type and what form/concentration of vitamin C and the pH level it can handle. All of this may dictate whether you end up with a lotion, serum, gel, etc. and therefore at which step to include it in your routine, but in general, you will want to apply it to clean, dry skin before any other moisturizers or SPFs. As a rule of thumb, no matter what your skin type, when introducing vitamin C to your routine, it is best to start by using your selected product a few times a week and build up to daily or twice daily use to avoid or limit any possible irritation. And of course, don’t forget to also apply it to your chest, neck, and the backs of your hands so that these areas benefit as much as your face will.

NORMAL AND OILY SKIN
For those with normal or oily skin, L-ascorbic is probably your best bet as it is the strongest and most effective proven form (remember, the studies are limited on other types like THD), and therefore you will see better results faster. Because you don’t struggle with sensitivity, you can start at a higher concentration of vitamin C (between 15% and 20%), and a lower pH, around 3.5 or 4.

SENSITIVE, COMBINATION, AND DRY SKIN
For those with sensitive or combination skin, L-ascorbic acid may be too powerful and irritating. Look for products that use the vitamin C derivatives sodium ascorbyl phosphate or magnesium ascorbyl phosphate which will be more gentle on the skin. Start at a lower concentration of vitamin C (between 5% and 10%) and a pH that is closer to the skin’s natural pH level, between 5 and 7.

Because vitamin C helps to protect against free radicals, dermatologists have always recommended applying it as part of your morning routine to prevent damage during the day. However, after a 2015 Yale University study revealed that UV damage can continue even after you’ve left the sun, it became widely accepted that incorporating antioxidants into your evening routine has its benefits.

While vitamin C plays well with most other active ingredients, its effectiveness can decrease when used alongside niacinamide, so avoid this ingredient in other skin care while using vitamin C. Because vitamin C lacks stability, you should also avoid layering it with alpha- and beta- hydroxy acids such as glycolic, salicylic, and lactic acids––essentially anything that acts as an exfoliant.