When you pick up most skincare products, you’ll notice the first ingredient is usually water. Given that laws generally require companies to list ingredients from highest to lowest concentration (with the exception of those under 2%, which can be listed in any order), this means that you’ll be putting mostly water-based skincare on your skin. (Most products feature about 70-80% water).
However, water is starting to come under question as the optimal base for skincare. Yes, it’s been used for years because it’s cheap, an excellent solvent, and a pH balancer and “heaviness” cutter for many other ingredients.
But, contrary to popular belief, water in and of itself isn’t great for hydrating the skin. Yes, it is if you drink it, but when it’s topically applied, water can actually be drying for susceptible folks. (This is why certain people’s skin often feels tight or dry after a shower). Water also isn’t a great solvent for keeping unstable ingredients like L-ascorbic acid stable.
Nowadays, nanoemulsions are becoming popular. Nanoemulsions are very fine (less than 100 nm) water-in-oil emulsions. They penetrate the skin quickly, hydrate well, and ensure greater stability of ingredients like L-ascorbic acid (Advances in Colloid and Interface Science, 2004). They have been shown to penetrate the skin so well, in fact, that they’re being examined for use as a drug delivery system (International Journal of Pharmaceutics, 2008). The most popular nanoemulsion in skincare today is The Ordinary Vitamin C Suspension 23% + HA Spheres 2%, which features zero water.
Other newly popular options are mix-in ingredients, like the powdered Clinique Fresh Pressed Vitamin C Powder, which is mixed with water-based serums or moisturizers, but which keep the vitamin C fresh until you’re ready to apply it. My sources say freeze-dried ingredients are also in the works at several facilities, but their introduction is likely a few years off.
Bottom line: If you’re a skincare fanatic who wants optimal activity from his/her skincare, using a nanoemulsion or mix-in powder ingredient isn’t a bad idea, particularly if you’re concerned about degradation of antioxidants over time. On the other hand, how much difference this makes remains to be seen. I would say, if you use a vitamin C serum within a month of opening it, it probably doesn’t matter all that much. But if you are the type who opens and closes the bottle over the course of months, exposing the product to all of that antioxidant-degrading air into the bottle each time, I would say, switch on over.