I’ve been asked a lot for my opinion on a recent article on whether vitamin C serums are bad for your skin. In the article, Wendy explains why Oumere will never have a vitamin C serum in their line. She outlines that vitamin C can:
- Act as a pro-oxidant when it reacts with iron in the air (or iron and copper in cosmetics) via the Fenton reaction, leading to irritation, collagen and elastin breakdown and acne
- Lead to desensitisation (tachyphylaxis) so if you start using it too young, your skin won’t respond later on
Let’s take a look at both of these arguments.
Is Vitamin C Pro-oxidant?
While in some circumstances vitamin C can act as a pro-oxidant after it reacts with metals and potentially lead to collagen destruction, vitamin C is also known to have effects that are the exact opposite:
- Vitamin C on its own is a potent antioxidant that soaks up free radicals and prevents the oxidative damage that results from UV light and other environmental stressors, as well as normal biological processes
- Vitamin C is an essential cofactor that’s required for enzymes that crosslink and stabilise collagen (prolyl and lysyl hydroxylase)
So how do we tell which of these actions, pro-oxidant or antioxidant, wins out? Science, of course! More specifically, we have quite a lot of clinical trials on vitamin C where vitamin C serums are applied to actual human skin, and its effect is measured. Vitamin C is one of THE best researched skincare ingredients.
None of the clinical trials on topical vitamin C (that’s vitamin C applied to the skin) found a decrease in collagen. In fact, a whole bunch of studies found that vitamin C increased collagen. In these studies, the volunteers were also exposed to air pollution and other cosmetic products, which were proposed to be the sources of metals that would cause a pro-oxidant effect in the article. Clearly the antioxidant effect is winning.
Related Post: Antioxidants in Skincare: What Do They Do?
Studies where vitamin C increased collagen:
- BV Nusgens et al., Stimulation of collagen biosynthesis by topically applied vitamin C (open access), Eur J Dermatol 2002, 12, 32-34.
- BV Nusgens et al., Topically applied vitamin C enhances the mRNA level of collagens I and III, their processing enzymes and tissue Inhibitor of matrix metalloproteinase 1 in the human dermis (open access), J Invest Dermatol 2001, 116, 853-859. DOI: 10.1046/j.0022-202x.2001.01362.x
- RE Fitzpatrick & EF Rostan, Double-blind, half-face study comparing topical vitamin C and vehicle for rejuvenation of photodamage (PDF link), Dermatol Surg 2002, 28, 231-236.
- M Haftek et al., Clinical, biometric and structural evaluation of the long-term effects of a topical treatment with ascorbic acid, Exp Dermatol 2008, 17, 946-952. DOI: 10.1111/j.1600-0625.2008.00732.x
Most studies on vitamin C measure its effect on photodamage. These studies generally measure the effect of vitamin C on wrinkles. While this isn’t a direct measure of collagen, lack of collagen causes deeper wrinkles, so if vitamin C was having a pro-oxidant effect you’d see a worsening of photodamage (which is actually caused partially by increased oxidation). In these studies, vitamin C improved photodamage:
