Vitamin C, an active ingredient with hydrating properties?

The vitamin C, or ascorbic acid, is one of the most studied antioxidants in dermatology and cosmetics. It indeed has a significant capacity to neutralize the free radicals generated by UV radiation, pollution, and the oxidative stress internal. 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. Furthermore, several studies have shown that vitamin C could stimulate collagen synthesis. Indeed, it is a cofactor for prolyl and lysyl hydroxylase enzymes required for the hydroxylation of procollagen chains. Vitamin C therefore helps maintain the stability and density of the extracellular matrix and has a preventive effect on skin aging. Finally, vitamin C is an effective active ingredient for hyperpigmentation, as it reduces tyrosinase activity, the enzyme that converts tyrosine into melanin.

Despite all the benefits it provides to the skin, vitamin C does not appear to have a genuinely hydrating effect.

However, although vitamin C does not directly influence the skin’s water balance, one can consider an indirect hydrating effect related to its impact on the skin barrier. Indeed, multiple studies have demonstrated that vitamin C stimulates the production of ceramides, the lipids in the stratum corneum that limit transepidermal water loss. In a study 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 to calcium alone. This rise was attributed to increased 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, thereby potentially reducing water loss.

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

The same holds true for oral vitamin C intake, which does not seem to exert any notable effect on skin hydration. Available clinical data show that even when vitamin C is incorporated into dietary supplements, it does not improve skin hydration in a measurable way. A double-blind, placebo-controlled trial involving 87 women over 16 weeks assessed the impact of daily supplementation with hydrolyzed collagen plus 80 mg of vitamin C (CP), or collagen + vitamin C + 30 mg of hyaluronic acid (CPHA), compared with a placebo. The results revealed benefits in dermal density, skin 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, although it is recognized for its hydrating properties when applied topically, did not produce any noticeable difference.

In summary, despite its numerous benefits for the skin (antioxidant action, collagen support, improved uniformity of complexion), vitamin C has not demonstrated a direct moisturizing effect, either when applied topically or 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).