Vitamin C, an active ingredient with moisturising properties?

The vitamin C, or ascorbic acid, is one of the most extensively studied antioxidants in dermatology and cosmetics. It indeed has a substantial capacity to neutralise free radicals generated by UV, pollution and the internal oxidative stress. Thanks to its role as an electron donor, vitamin C interrupts the chain reactions responsible for the oxidation of skin lipids and the alteration of structural proteins. Moreover, several studies have shown that vitamin C can stimulate collagen synthesis. Indeed, it acts as a cofactor for prolyl and lysyl hydroxylases, necessary for the hydroxylation of procollagen chains. Vitamin C thus contributes to the maintenance of extracellular matrix stability and density and has a preventive effect on skin ageing. Finally, the vitamin C is an effective agent against hyperpigmentation, as it reduces the activity of tyrosinase, the enzyme that converts tyrosine into melanin.

Despite all the benefits it confers on the skin, vitamin C does not appear to have a strictly hydrating effect.

Nevertheless, although vitamin C does not directly participate in the skin’s water balance, one may envisage an indirect hydrating effect linked to its impact on the skin barrier. Indeed, several studies demonstrate that vitamin C stimulates the production of ceramides, the lipids of the stratum corneum that limit insensible water loss. In a study conducted on human keratinocytes cultured for 11 days with calcium (1.2 mM) and vitamin C (50 μg/ml), researchers observed a significant increase in total ceramide content compared with calcium alone. This rise is attributed to elevated expression and activity of serine-C-palmitoyltransferase and ceramide synthase, two enzymes involved in ceramide assembly.

This action of vitamin C results in a more functional skin barrier and thus a potential reduction in water loss.

However, when examining clinical studies on the topical application of vitamin C, none demonstrate a hydrating effect attributable solely to vitamin C when compared to a control (an identical cream without vitamin C). Clinical trials report improvements in skin radiance and firmness, but never a direct increase in skin hydration. Studies reporting enhanced hydration involve complete formulations containing both vitamin C and other active humectants, emollients or film-forming agents. Under these conditions, it is impossible to isolate the contribution of vitamin C, with the observed hydrating effect more likely deriving from the cream itself (its texture, lipids and humectants).

The same applies to the oral intake of vitamin C, which does not appear to exert any notable effect on skin hydration. The available clinical data show that even when vitamin C is incorporated into dietary supplements, it does not measurably improve skin hydration. A double-blind, placebo-controlled study involving 87 women over 16 weeks evaluated the impact of daily supplementation with hydrolysed collagen combined with 80 mg of vitamin C (CP), or with collagen + vitamin C + 30 mg of hyaluronic acid (CPHA), compared with a placebo. The results showed benefits in dermal density, texture and wrinkle severity, but no significant improvement in hydration in the CP or CPHA groups compared with placebo. Even the addition of hyaluronic acid, despite being recognised for its hydrating properties when applied topically, did not create any notable difference.

In summary, despite its numerous benefits for the skin (antioxidant action, collagen support, improvement of skin‐tone uniformity), vitamin C has not demonstrated any direct hydrating effect, either when applied topically or when taken as a dietary supplement.

• TELANG P. S. Vitamin C in dermatology. Indian Dermatology Online Journal (2013).

• CHO Y. & al. Vitamin C stimulates epidermal ceramide production by regulating its metabolic enzymes. Biomolecules & Therapeutics (2015).

• VISSERS M. & al. The roles of vitamin C in skin health. Nutrients (2017).

• BOO Y. C. & al. Ascorbic acid (vitamin C) as a cosmeceutical to increase dermal collagen for skin antiaging purposes: Emerging combination therapies. Antioxidants (2022).

• POGACNIK T. & al. The effects of dietary supplementation with collagen and vitamin C and their combination with hyaluronic acid on skin density, texture and other parameters: A randomised, double-blind, placebo-controlled trial. Nutrients (2024).