Vitamin C: What are its benefits for the skin?

While vitamin C is widely recognized for its antioxidant role, it can, paradoxically, adopt a pro-oxidant behavior under certain conditions. This phenomenon relies on its ability to reduce metal ions such as iron (Fe³⁺ to Fe²⁺) or copper (Cu²⁺ to Cu⁺), which then participate in Fenton reactions generating highly reactive hydroxyl radicals from hydrogen peroxide. However, this pro-oxidant potential appears limited in vivo, as the body controls the availability of free metals through proteins like ferritin or transferrin, which effectively sequester iron.

Vitamin C can also be an ally in combating the signs of aging. In addition to its antioxidant action, which helps protect the skin’s structural fibers from oxidative degradation, it may regenerate the dermis by stimulating collagen synthesis. Studies in vitro have indeed shown that ascorbic acid promotes the expression of genes encoding type I and III collagen chains, the main components of the dermal extracellular matrix. Vitamin C is also a cofactor for two enzymes involved in the hydroxylation of proline and lysine, a critical step in stabilizing the triple-helix structure of collagen. By improving both the quantity and quality of the fibers produced, vitamin C would help reinforce skin firmness and soften wrinkles.

Several clinical studies have highlighted the value of vitamin C in caring for skin prone to photoaging. One of these was conducted on 20 women aged 30 to 50 years with high UV exposure to evaluate the effects of cosmetic treatments formulated with vitamin C and SH-polypeptide-10, a recombinant peptide. After daily application for two weeks, the results showed a significant improvement in periorbital wrinkles and skin radiance, accompanied by a notable reduction in pigmentation, which supports the idea that vitamin C is a relevant active ingredient for targeting the various signs of photoaging.

In addition to its antioxidant and depigmenting properties, vitamin C also plays a protective role in maintaining the skin barrier and countering inflammation. This benefit relies on several complementary mechanisms. By neutralizing reactive oxygen species, vitamin C limits the activation of pro-inflammatory signaling pathways such as NF-κB, which is known to drive the production of cytokines like IL-1β, IL-6, and TNF-α. This active agent also promotes ceramide synthesis by regulating the activity of enzymes such as S1P phosphatase. That is why vitamin C can be beneficial for dry skin or compromised skin.

This potential was demonstrated in a murine model of atopic dermatitis, a chronic inflammatory condition characterized by dry, red, and itchy skin. Researchers used a protected form of vitamin C (NXP081), combined with a single-stranded DNA aptamer designed to limit its oxidation. In mice given this formulation orally after eczema was induced by topical DNFB application, a significant reduction in ear edema was observed, along with visible improvement of skin lesions. Mast cell infiltration within the lesions also declined, as did interferon-gamma production by activated CD4+ T lymphocytes. These results suggest that vitamin C, when stabilized, can limit inflammatory responses and partially restore immune balance in the context of atopic dermatitis. Of course, these findings still need to be confirmed in humans and for topical use.

Beyond inflammatory pathologies, vitamin C proves useful for counteracting the cumulative effects of environmental stress on the skin. A study ex vivo evaluated the consequences of combined exposure to atmospheric pollutants (ozone, fine particles from a diesel engine) and UV, mimicking an extreme oxidative stress scenario. Human skin explants were exposed to these insults for four days, with or without prior incubation in an antioxidant solution containing 15% vitamin C, 1% vitamin E, and 0.5% ferulic acid. The results showed a marked loss of desmocollin, claudin, and aquaporin-3, proteins involved in the cohesion and hydration of the skin barrier, as well as activation of the inflammasome, a protein complex that responds to danger signals. Preincubation with the antioxidant treatment significantly prevented these alterations, demonstrating the value of indirect photoprotection by antioxidants in an urban context.

Vitamin C is also involved in the various stages of the wound healing, beyond its well-known function in collagen synthesis. In wounds undergoing repair, insufficient vitamin C levels are frequently observed, which can delay inflammation resolution and compromise tissue reconstruction. Studies in vitro have shown that ascorbic acid can modulate the expression of mediators such as HO-1, TGF-β, and VEGF, all three essential to fibroblast migration, neovascularization, and extracellular matrix deposition. This compound could thus be useful for supporting the healing of damaged skin.

These initial findings led to exploring the efficacy of vitamin C in clinical trials. A study by SARPOOSHI and colleagues in 2021 involved 30 patients with extensive second-degree burns. The participants, randomly assigned to two groups, all received standard care with a 1% silver sulfadiazine solution, but only one group received an adjunctive treatment with a 10% vitamin C solution. Wound progression was monitored over 14 days and a significantly greater improvement in patients treated with vitamin C was observed. Ascorbic acid thus appears to accelerate the skin regeneration process, likely by limiting local oxidative damage, supporting collagen synthesis, and modulating the local inflammatory response.