Vitamin C serum is one of the most searched-for and best-selling skincare products. It is also one of those in which the difference between a product that works and one that does almost nothing is greatest, and least visible from the outside. The price and the percentage displayed prominently on the packaging say little. Other factors matter, and you can learn to read them in just a few minutes.
In summary
- Vitamin C is an antioxidant that helps even out the complexion, supports collagen, and complements sun protection.
- Five things matter when choosing it: form, concentration, pH, packaging, and accompanying ingredients.
- Use it in the morning, before moisturizer and sunscreen.
- Radiance in a few weeks, dark spots and firmness over several months. It never replaces SPF.
Article written by Elisa Avalle, founder of LeLang Skin Care and dermocosmetics specialist. Cover image generated with the support of artificial intelligence.
[INDICE:h2]
What it does, and what to expect
Vitamin C does three things for the skin, all well documented. It neutralizes the free radicals produced by the sun and pollution. It is necessary for the enzymes that stabilize collagen. And it slows the activity of tyrosinase, the enzyme that produces melanin.
In terms of results: a more even, radiant complexion, help preventing new dark spots, and support for skin firmness over time. In clinical studies on photoaging, improvements were measured after about three months of daily use. Radiance appears first, followed by fine lines and dark spots.
The molecule’s chemistry, forms, and mechanism are explained in the glossary entry: ascorbic acid and vitamin C. Here we focus on how to choose it.
The five criteria for choosing
1. The form of vitamin C
In the INCI, "vitamin C" may correspond to different molecules. The two main families are:
- Pure ascorbic acid (Ascorbic Acid): the most studied and most potent form, but also the most unstable and the most difficult to tolerate, because it works only at a very acidic pH.
- Stabilized derivatives: for example, 3-O-Ethyl Ascorbic Acid, Sodium Ascorbyl Phosphate, Magnesium Ascorbyl Phosphate, Ascorbyl Glucoside, Tetrahexyldecyl Ascorbate. They oxidize much less, are gentler, and work at a pH closer to that of the skin.
The practical rule: pure ascorbic acid is the most intense choice for those who tolerate it; derivatives are the most sensible choice for reactive skin, beginners, and anyone who wants a product that remains active for longer after opening. There is a dedicated guide to one of the most widely used derivatives: sodium ascorbyl phosphate.
2. The concentration
For pure ascorbic acid, studies indicate a useful range of approximately 8% to 20%. Below that, the effect is weak; above that, it does not increase, but irritation does. For derivatives, the situation is different: each has its own effective concentration, and 5% of a derivative is not "less" than 15% pure acid. Figures for different forms cannot be compared.
3. The pH
It is the least disclosed piece of information and one of the most important. Pure ascorbic acid penetrates the skin only below pH 3.5: a pure acid serum at neutral pH is almost inert. Stabilized derivatives do not have this limitation, which is one of the reasons they are better tolerated.
4. The packaging
Air, light and heat degrade vitamin C. Opaque or airless bottles, dark glass dropper bottles, and small sizes to finish within a few weeks are preferable. A transparent jar opened every morning is the worst possible packaging.
5. The ingredients that accompany it
The most studied combination is vitamin C with vitamin E and ferulic acid: a 2005 study showed that ferulic acid stabilizes the formula and doubles the antioxidant photoprotection provided by vitamins C and E together. A humectant such as hyaluronic acid makes the serum more comfortable. And vitamin C can be combined with niacinamide, despite the contrary myth: this is explained in vitamin C and niacinamide together.
How to use it
- In the morning, on cleansed, dry skin: this is when its antioxidant action complements the day's exposure.
- A few drops for the face and neck, gently patted in without rubbing.
- Then moisturizer, if needed, and always sunscreen.
- In the evening, leave room for retinoids or exfoliants, which are best not layered with vitamin C in the same application when starting out.
Those with sensitive skin can start by using it every other day for two weeks and then switch to daily use.
FERULIC + HA SERUM Brightening antioxidant serum for the face based on Vitamin C & Ferulic AcidEFFECTS: Lightens blemishes Stimulates c... Discover FERULIC + HA SERUM
Our Ferulic + HA serum uses vitamin C in the form of 3-O-ethyl ascorbic acid, a stable derivative, together with ferulic acid, vitamin E, and hyaluronic acid: this is the combination described in point 5, designed for daily morning use.
The most common mistakes
- Use it instead of sunscreen. Vitamin C is not a filter: it works downstream, on the free radicals that form anyway. Without SPF, its effect on dark spots is lost.
- Keep it in the bathroom or on the windowsill. Heat and light oxidize it quickly.
- Keep using it once it has turned orange. A straw yellow color can be normal; orange or amber indicate that the active ingredient has degraded.
- Judge it after two weeks. Reducing dark spots and improving firmness take months of consistent use.
- Choosing based on price or the highest percentage. An expensive serum with the wrong pH, or a 20% serum that causes irritation and is abandoned after a week, delivers less than a well-formulated derivative used every day.
Frequently asked questions
The vitamin C serum tingles: is that normal?
A slight tingling sensation may occur during the first few days with pure ascorbic acid because of its low pH. If the burning persists or redness appears, it is better to switch to a stabilized derivative or reduce the frequency.
Is it also suitable for oily or blemish-prone skin?
Yes, by choosing a lightweight texture. Some derivatives, such as sodium ascorbyl phosphate, also have data supporting their use on acne-prone skin.
At what age can you start?
There is no minimum age. As an antioxidant, it works mainly as a preventive measure: it makes sense from the time sun exposure becomes a daily occurrence.
Can it be used in summer?
Yes, and in fact this is the time when its antioxidant action is most useful, always together with sun protection. Vitamin C does not make the skin more sensitive to the sun.
The next step
The pharmacist at LeLang partner pharmacies and parapharmacies can help you understand whether you need a vitamin C serum and how to incorporate it into your existing routine, especially if your skin is reactive or you are using other active ingredients.
Want to understand where to start?
Book a free virtual consultation: together, we will assess your skin and the most suitable routine.
Sources for this article
- Pinnell S.R. et al. (2001). "Topical L-ascorbic acid: percutaneous absorption studies". Dermatologic Surgery, vol. 27, no. 2, pp. 137-142.
- Lin F.H. et al. (2005). "Ferulic acid stabilizes a solution of vitamins C and E and doubles its photoprotection of skin". Journal of Investigative Dermatology, vol. 125, no. 4, pp. 826-832.
- Traikovich S.S. (1999). "Use of topical ascorbic acid and its effects on photodamaged skin topography". Archives of Otolaryngology, Head and Neck Surgery, vol. 125, no. 10, pp. 1091-1098.
- Telang P.S. (2013). "Vitamin C in dermatology". Indian Dermatology Online Journal, vol. 4, no. 2, pp. 143-146.
Where to continue: Ascorbic acid and vitamin C · Ferulic acid · Facial discoloration
Discover the products: Brighten
