Vitamin C: What are its benefits for the skin?

The vitamin C is first and foremost known for its potent antioxidant properties which allow it to protect the skin from free radicals. They are generated by several factors, including UV rays, pollution, cigarette smoke, excessive alcohol consumption and stress... Free radicals are molecules lacking an electron. Highly reactive and therefore unstable, they tend to react with the body's healthy molecules, damaging cells and tissues. This process, known as "oxidative stress", accelerates skin ageing, and thus leads to the appearance of wrinkles and pigmentation spots. Ascorbic acid, by donating an electron, can neutralise free radicals. It is then converted into dehydroascorbic acid, which is relatively stable due to its aromatic cyclic structure.

While vitamin C is widely acknowledged for its antioxidant role, it can, paradoxically, take on a pro-oxidant behaviour under certain conditions. This phenomenon is based on its ability to reduce metal ions, such as iron (Fe³⁺ to Fe²⁺) or copper (Cu²⁺ to Cu⁺), which then participate in Fenton reactions, producing highly reactive hydroxyl radicals from hydrogen peroxide. However, this pro-oxidant potential appears to be limited in vivo, as the organism regulates the availability of free metals through proteins such as ferritin and transferrin, which efficiently sequester iron.

The vitamin C is also frequently used in cosmetics for its brightening effects, particularly on age-related pigmentation spots, those resulting from repeated sun exposure or past skin inflammations. This tone-unifying action largely relies on its ability to interfere with the melanogenesis process, that is to say the synthesis of melanin. More precisely, ascorbic acid inhibits the activity of tyrosinase, an enzyme that catalyses the oxidation of tyrosine to DOPA and then to DOPAquinone, the initial steps towards melanin formation. By disrupting this process, vitamin C reduces the production of brown pigments in melanocytes, thereby helping to fade existing spots and prevent the emergence of new ones.

A double-blind study was carried out in 27 Japanese women with solar lentigines. Over 24 weeks, a lotion containing 6% trisodium L-ascorbate-2-phosphate salt, a stable form of vitamin C, was applied twice daily to one side of the face, while the other side received a placebo. The outcomes, measured by colourimetric devices such as the Mexameter, demonstrated a significantly greater enhancement in facial luminosity in those treated with the vitamin C derivative. Furthermore, 7 of the 27 participants exhibited a marked improvement in pigmented spots, compared to none in the placebo group.

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

Several clinical studies have highlighted the benefits of vitamin C in caring for skin prone to photoageing. One such study involved 20 women aged 30 to 50 with high UV exposure, to assess the effects of cosmetic formulations containing vitamin C and SH-polypeptide-10, a recombinant peptide. Following daily application over two weeks, the results demonstrated a significant improvement in periocular wrinkles and skin radiance, accompanied by a marked reduction in pigmentation, reinforcing the notion that vitamin C is a relevant active ingredient for targeting various signs of photoageing.

In addition to its antioxidant and depigmenting properties, vitamin C also plays a protective role with respect to the skin barrier and inflammation. This benefit is underpinned by several complementary mechanisms. By neutralising reactive oxygen species, vitamin C limits the activation of pro-inflammatory signalling pathways, such as NF-κB, known to promote the production of cytokines like IL-1β, IL-6 and TNF-α. This active ingredient also stimulates ceramide synthesis by regulating the activity of enzymes such as S1P phosphatase. That is why vitamin C can be interesting for the dry skin or compromised.

This potential was demonstrated in a murine model of atopic dermatitis, a chronic inflammatory condition characterised by dry, red and itchy skin. The researchers used a protected form of vitamin C (NXP081), coupled to a single-stranded DNA aptamer to limit its oxidation. In mice given this formulation orally after inducing eczema by applying a DNFB solution, there was a significant reduction in ear swelling, along with visible improvement in skin lesions. Mast cell infiltration into the lesions also decreased, as did interferon-gamma production by activated CD4+ T lymphocytes. These results suggest that, when stabilised, vitamin C can limit inflammatory responses and partially restore immune balance in the context of atopic dermatitis. These results, of course, remain to be confirmed in humans and for topical application.

Beyond inflammatory conditions, vitamin C proves valuable for counteracting the cumulative effects of environmental stressors on the skin. An ex vivo study evaluated the effects of combined exposure to atmospheric pollutants (ozone, fine particles from a diesel engine) and UV radiation, replicating an extreme oxidative stress scenario. Human skin explants were subjected to these insults for four days, with or without pre-incubation in an antioxidant solution containing 15% vitamin C, 1% vitamin E and 0.5% ferulic acid. The results revealed a marked loss of desmocollin, claudin and aquaporin-3—proteins critical for the cohesion and hydration of the skin barrier—as well as activation of the inflammasome, a protein complex that responds to danger signals. Pre-treatment with the antioxidant formulation significantly prevented these alterations, demonstrating the benefit of indirect photoprotection by antioxidants in an urban context.

Vitamin C is also involved in the various stages of the process of wound healing, beyond its well-known role in collagen synthesis. In wounds undergoing repair, insufficient vitamin C levels are frequently observed, which can delay the resolution of inflammation and impair 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 for fibroblast migration, neovascularisation and extracellular matrix deposition. This active compound could therefore be useful to support the healing of damaged skin.

These initial findings prompted an investigation into the efficacy of vitamin C in clinical trials. A study carried out by SARPOOSHI and colleagues in 2021 involved 30 patients with extensive second-degree burns. The participants, randomly divided into two groups, all received standard treatment with a 1% silver sulfadiazine solution, but only one group also received an adjunct therapy with a 10% vitamin C solution. Wound progression was monitored for 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 inflammatory response.

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