The myths surrounding vitamin C.

True and false.

Often it is believed that "vitamin C" and "ascorbic acid" refer to exactly the same substance, but this is not entirely accurate. The vitamin C actually corresponds to one of the two forms of ascorbic acid. Indeed, we distinguish L-ascorbic acid, which is biologically active in humans and naturally found in plants, fruits and certain micro-organisms, from D-ascorbic acid, a mirror form that has no vitamin activity. It is therefore only L-ascorbic acid that can be called vitamin C, as it is this form that our body can utilise in its physiological processes, notably in the synthesis of collagen and in protection against oxidative stress.

Vitamin C is always ascorbic acid, whereas ascorbic acid is not always vitamin C.

False.

It is sometimes said that only skincare products containing pure vitamin C, that is L-ascorbic acid, are truly effective. Yet, it is not that simple. Ascorbic acid is a powerful but temperamental molecule. Very unstable in aqueous solution, it oxidises rapidly on exposure to light, air and heat. This instability presents a major formulation challenge. For ascorbic acid to remain active and penetrate the skin barrier, it requires a very acidic pH (below 3.5). However, this low pH can cause irritation, particularly in sensitive skin.

Although L-ascorbic acid is extremely effective, it does have several limitations, which is why there is interest in derivatives of vitamin C, such as Sodium Ascorbyl Phosphate or 3-O-Ethyl Ascorbic Acid.

These derivatives of vitamin C are not diluted or less effective versions: they are alternative forms that deliver similar benefits while overcoming its limitations. Numerous scientific studies indeed support their potential. One study in particular assessed the impact of L-ascorbic acid, as well as vitamin C phosphate (VitC-P) and vitamin C glucoside (VitC-Glu) on collagen synthesis. The researchers observed that vitamin C stimulates type I collagen production by human fibroblasts in a dose-dependent manner (10⁻⁵ M to 10⁻³ M). It also promotes extracellular matrix contraction, a hallmark of tissue strengthening.

Interestingly, VitC-P and VitC-Glu demonstrated similar effects.

The study concludes by stating that these derivatives of vitamin C can act as pro-vitamins that are converted in the skin into active ascorbic acid, and that they represent interesting alternatives for formulating more stable and better-tolerated vitamin C treatments.

False.

Contrary to a persistent misconception, the vitamin C can readily be combined with other cosmetic actives, and these combinations are often very beneficial. It, for example, works particularly well with the niacinamide, whose soothing properties and ability to reinforce the skin barrier compensate for any potential irritant effect of ascorbic acid. When combined with the vitamin E, it forms a synergistic antioxidant duo that effectively neutralises free radicals, while the addition of hyaluronic acid contributes to maintaining hydration and improving skin comfort.

In short, vitamin C is not a standalone molecule, and its effectiveness can be enhanced when integrated into a well-designed regimen.

False.

Contrary to a widespread misconception, vitamin C is not photosensitising in the slightest. It does not make the skin more vulnerable to UV radiation, as some AHAs, and there is no evidence that it increases the risk of sunburn. The confusion actually stems from its instability: L-ascorbic acid oxidises in light, leading to a change in colour and a loss of efficacy. To minimise this degradation, formulations are often very acidic, which can cause irritation sometimes mistaken for photosensitisation.

In reality, it’s the opposite: vitamin C exhibits photoprotective properties thanks to its potent antioxidant role.

It does not act as a sunscreen (it does not absorb UV), but it helps to neutralise free radicals generated by sun exposure, thereby helping to limit oxidative damage. Skin levels of vitamin C decrease after UV exposure, so its regular application, before and after sun exposure, supports the skin’s natural defences. It does not replace a sun protection, but it adds an extra layer of defence.

True and false.

This myth is both true and false: it all depends on the form of vitamin C and its concentration. Pure L-ascorbic acid can irritate sensitive skin, particularly when formulated at low pH or in high concentrations, but this reaction is not systematic and relates more to individual tolerance than to a general incompatibility. Conversely, stabilised derivatives of vitamin C are often much better tolerated owing to their gradual release into the skin. They enable one to enjoy the antioxidant benefits of vitamin C while mitigating the risk of irritation. In any case, a tolerance test is good practice to progressively adjust the use of vitamin C.

False.

This myth is false: the vitamin C can, on the contrary, be beneficial for acne-prone skin. Several studies, both in topical application and oral administration, show that it helps to reduce inflammation, a key factor in lesion formation. Its antioxidant activity also limits the oxidative stress present in inflamed areas, while supporting skin repair and helping to fade post-inflammatory marks. Vitamin C obviously does not replace a medical protocol, but it can be a valuable asset in the overall improvement of skin condition.

A recent preclinical study provides interesting insights. A combination of encapsulated adapalene and vitamin C was tested in a murine model of testosterone-induced acne. The researchers compared several groups (adapalene alone, encapsulated or not; encapsulated combination; acne control; and healthy control) and found that the gel combining encapsulated adapalene and vitamin C was the one that most effectively reduced inflammation and lesion size, whilst restoring skin structure closer to normal. Although these results, obtained in animals, cannot be directly extrapolated to humans, they suggest a possible synergistic effect between the two active agents and reinforce the idea that vitamin C could have a complementary role in the management of acne-prone skin.

True.

Indeed, the human body is unable to produce its own vitamin C. This inability stems from a mutation in the gene encoding the enzyme L-gulonolactone oxidase, which is essential for the final step of vitamin C synthesis in most vertebrates. This enzymatic deficiency renders humans entirely dependent on their diet to meet their physiological requirements for vitamin C. By comparison, many animals synthesise this vitamin themselves in the liver. This dietary reliance obliges humans to ensure an adequate intake to prevent deficiency-related diseases, such as scurvy.

True and false.

It is common to consider vitamin C a miracle cure for the common cold, but the reality is more nuanced. While it plays an essential role in supporting the immune system by contributing to the antioxidant defences of immune cells such as lymphocytes, macrophages and dendritic cells, supplementing does not guarantee the avoidance of a viral infection. The efficacy of vitamin C depends largely on the performance of our own immune system: the faster and more effectively it can respond to a virus, the more the antioxidant role of vitamin C will help to optimise the immune response. Thus, supplementation does not replace a functional immune system, but can help to support it in its action.

True and false.

Supplementation with vitamin C, particularly at high doses (≥1000 mg/day), has been associated with an increased risk of kidney stone development, especially in men. This risk is explained by the fact that vitamin C is metabolised into oxalate, a compound that can contribute to the formation of calcium oxalate stones. Some studies in cancer patients receiving prolonged doses around 500 mg have shown a higher incidence of new stones, with the risk increasing alongside cumulative dose and treatment duration. In healthy individuals, adverse effects remain rare, but particular caution is advised for those with a history of stones or impaired renal function. It should be noted that moderate vitamin C intake may have a protective effect against stone formation, although this benefit disappears at high doses.

In short, the risk of kidney stones depends primarily on the dose of vitamin C consumed, which underscores the importance of following your doctor’s recommendations and avoiding self-supplementation.

False.

Contrary to this common misconception, vitamin C does not have a stimulating effect and does not interfere with sleep. On the contrary, several studies suggest that an adequate intake of vitamin C could even promote better-quality sleep. Higher serum levels of vitamin C are associated with a reduced risk of sleep disorders, particularly in women and in individuals under 65 years of age. Its antioxidant properties may help to reduce oxidative stress, known to disrupt sleep, and animal models demonstrate that vitamin C supplementation protects against the cognitive deficits associated with sleep deprivation. Thus, far from hindering sleep, vitamin C appears to support its quality and regularity.

False.

Although the orange is often regarded as the flagship fruit of vitamin C, it is not the richest source of this nutrient. Other fruits exhibit even higher concentrations of vitamin C, such as blackcurrant, kiwi, guava and acerola, which have levels far exceeding those of the orange. Thus, while the orange remains an excellent source of vitamin C, there are even more concentrated alternatives to vary and optimise your daily intake.

• BERNARD B. A. & al. Effect of vitamin C and its derivatives on collagen synthesis and cross-linking by normal human fibroblasts. International Journal of Cosmetic Science (2001).

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

• TAYLOR E. N. & al. Total, dietary, and supplemental vitamin C intake and risk of incident kidney stones. National Kidney Foundation (2016).

• DUBEY A. & al. Development and investigation of vitamin C-enriched adapalene-loaded transfersome gel: a collegial approach for the treatment of acne vulgaris. AAPS PharmSciTech (2020).

• AKOLKAR G. & al. Vitamin C: Historical perspectives and heart failure. Heart Failure Reviews (2021).

• DING Y. & al. Association between vitamin C in serum and trouble sleeping based on NHANES 2017-2018. Scientific Reports (2024).