The myths surrounding vitamin C.

True and false.

We often believe that "vitamin C" and "ascorbic acid" refer to exactly the same thing, but that's not entirely accurate. The vitamin C corresponds, in reality, to one of the two forms of ascorbic acid. Indeed, we distinguish L-ascorbic acid, which is biologically active in humans and naturally present in plants, fruits, and certain microorganisms, and D-ascorbic acid, a mirror-image form that has no vitamin activity. Thus, only L-ascorbic acid can qualify as vitamin C, since it's this form our body can use in its physiological processes, notably the synthesis of the collagen and protection against oxidative stress.

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

False.

It is sometimes claimed that only skincare products containing pure vitamin C, namely L-ascorbic acid, are genuinely effective. Yet it’s not that straightforward. L-ascorbic acid is a potent but capricious molecule. Highly unstable in aqueous solution, it oxidizes rapidly when exposed to light, air, and heat. This instability poses 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, such a low pH can be irritating, particularly for sensitive skin.

Although L-ascorbic acid is highly effective, it has several limitations, hence the interest in using 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 provide similar benefits while overcoming its limitations. Several scientific findings also support their relevance. One study specifically evaluated the impact of L-ascorbic acid, as well as vitamin C phosphate (VitC-P) and vitamin C glucoside (VitC-Glu), on collagen synthesis. Researchers observed that vitamin C stimulates, in a dose-dependent manner (10⁻⁵ M to 10⁻³ M), type I collagen production by human fibroblasts. It also enhances extracellular matrix contraction, a sign of tissue strengthening.

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

The study concludes by stating that these derivatives of vitamin C can act as provitamins that are converted in the skin into active ascorbic acid, offering promising alternatives for formulating more stable and better-tolerated vitamin C skincare products.

False.

Contrary to a persistent misconception, vitamin C can absolutely be combined with other cosmetic actives, and these combinations are often very beneficial. For example, it works particularly well with niacinamide, whose soothing properties and ability to strengthen the skin barrier counterbalance the potential irritant effects of ascorbic acid. When paired with vitamin E, it forms a synergistic antioxidant duo that effectively neutralizes free radicals, while the addition of hyaluronic acid helps maintain hydration and improve skin comfort.

In short, vitamin C is not a standalone molecule, and its efficacy can be amplified when it is integrated into a well-designed routine.

False.

Contrary to a widespread belief, the vitamin C is absolutely not photosensitizing. It does not make the skin more vulnerable to UV rays, 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 oxidizes when exposed to light, causing discoloration and a loss of efficacy. To limit this degradation, formulations are often very acidic, which can cause irritation sometimes mistaken for photosensitization.

In fact, the opposite is true: vitamin C exhibits photoprotective properties thanks to its potent antioxidant activity.

It doesn’t act like a sunscreen filter (it does not absorb UV rays), but it helps to neutralize the 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 defenses. It does not replace sunscreen, but it adds an extra layer of defense.

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, especially when formulated at a low pH or at high concentrations, but this reaction is not systematic and is more a matter of individual tolerance than of a generalized incompatibility. Conversely, stabilized vitamin C derivatives are often much better tolerated thanks to their gradual release into the skin. They allow you to enjoy the antioxidant benefits of vitamin C while reducing the risk of irritation. In any case, a tolerance test is a good practice to gradually adjust the use of vitamin C.

False.

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

A recent preclinical study provides intriguing insights. A combination of encapsulated adapalene and vitamin C was tested in a mouse model of testosterone-induced acne. Researchers compared several groups (adapalene alone, encapsulated or not, encapsulated combination, acne control, and healthy control) and observed that the gel combining encapsulated adapalene and vitamin C was the one that most effectively reduced inflammation and lesion size, while restoring skin structure closer to normal. Although these animal results cannot be directly extrapolated to humans, they suggest a potential synergistic effect between the two active compounds and support the idea that vitamin C could play a complementary role in managing acne-prone skin.

True.

Indeed, the human body cannot synthesize its own vitamin C. This inability stems from a mutation in the gene encoding the enzyme L-gulonolactone oxidase, which is essential in the final step of vitamin C synthesis in most vertebrates. This enzymatic deficiency renders humans entirely dependent on dietary intake to meet their physiological vitamin C requirements. In contrast, many animals synthesize this vitamin in the liver. This dietary dependence in humans makes it necessary to ensure sufficient intake to prevent deficiency-related diseases such as scurvy.

True and false.

It is common to regard vitamin C as a cure-all 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 defenses of immune cells such as lymphocytes, macrophages, and dendritic cells, supplementation does not guarantee avoidance of a viral infection. The effectiveness of vitamin C depends largely on the performance of our own immune system: the better it can respond swiftly and effectively to a virus, the more useful vitamin C’s antioxidant role will be in optimizing the immune response. Thus, supplementation does not replace a functional immune system but can help support it in its action.

True and false.

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

In brief, the risk of developing kidney stones largely depends on the amount of vitamin C consumed, underscoring the importance of adhering to your physician’s recommendations and avoiding self-supplementation.

False.

Contrary to popular belief, 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 vitamin C levels are associated with a reduced risk of sleep disorders, especially among women and individuals under 65. Its antioxidant properties may help lower oxidative stress, which is known to disrupt sleep, and animal models show that vitamin C supplementation protects against cognitive deficits linked to sleep deprivation. Thus, far from hindering sleep, vitamin C appears to support its quality and consistency.

False.

Although the orange is often considered the emblematic fruit of vitamin C, it is not the richest source of this nutrient. Other fruits contain 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 optimize 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).