A vitamin C serum is a concentrated facial product with a light texture, used in skincare mainly to brighten and even out skin tone. At Panakeia you will find it as the Vitamin C brightening serum, and you can look at the other options in the Facial serums category.
What a vitamin C serum is
A serum is a type of facial product with a higher concentration of active ingredients and a lighter, well-absorbed texture than a classic cream. It is applied after toning and before the cream, because its job is to bring a specific ingredient to the skin in a targeted form, in this case vitamin C. Unlike a day cream, which above all hydrates and protects the skin, this form of care focuses on one or two key ingredients in a higher concentration. That is precisely why serums are usually sold in smaller packs and used by the drop, not by the palmful. The look and texture differ depending on which form of the active ingredient the maker has chosen: some versions are almost clear and watery, others have a slightly yellowish tint from the very first use, which is directly linked to the concentration and form of vitamin C in the recipe.
Which forms of vitamin C are used in serums
Vitamin C is not always added to cosmetics in the same form. Formulators can choose from several chemical forms that differ in solubility and in how sensitive they are to their surroundings. The choice of form directly affects how long the product keeps its original composition after opening and how it behaves in combination with the other ingredients in the recipe. Some forms dissolve in water and suit lighter, gel textures, while others dissolve in oil and so combine better with the vegetable oils in the formula. The difference between the individual forms is not just a chemical curiosity; it also directly affects the texture and shelf life you can expect from a particular product. The following table sums up the most common forms you will meet on serum labels.
| Form of vitamin C | Properties |
|---|---|
| L-ascorbic acid | Pure, water-soluble form, sensitive to light, heat and air |
| Sodium Ascorbyl Phosphate | A more stable, water-soluble derivative |
| Magnesium Ascorbyl Phosphate | A derivative suited to water-based recipes, gentler on the skin |
| Tetrahexyldecyl Ascorbate | An oil-soluble ester, used for example in our Vitamin C serum |
L-ascorbic acid
L-ascorbic acid is the most researched and chemically purest form of vitamin C, but also the least stable. It breaks down under the influence of light, heat and oxygen, which is why serums with it are usually packed in opaque or dark bottles with a pump that limits contact with air at each use. If a product contains this form, makers usually recommend storing it out of direct sun and using it up within a few months of opening. The lower pH that this form requires can be more demanding for sensitive skin, so for gentler recipes formulators often lean towards derivatives. It is exactly this combination of a high active concentration and low stability that explains why this form is sold a little more expensively and in smaller packs than most ordinary skincare: the maker expects it to be used up within a fairly short time after opening.
Vitamin C derivatives (esters)
Vitamin C derivatives, such as the sodium salt of the phosphate, the magnesium salt of the phosphate or an oil-soluble ester, are created by attaching vitamin C to another molecule, which makes them more stable and less prone to breaking down. Oil-soluble forms, such as the one you will find in our Vitamin C brightening serum, also combine well with the oil ingredients in a recipe, in this case squalane or jojoba oil. The choice of a particular form is always a compromise between stability, texture and how well that form holds up in a particular type of recipe. For the everyday shopper this means in practice that it is worth looking at the ingredient list on the pack, not just at the words vitamin C in the marketing text, because it is the specific name in the INCI list that reveals which form the serum really contains and how long it keeps its original quality after opening.
Why the stability of vitamin C matters
Vitamin C is among the least stable cosmetic ingredients, which is why formulators pay special attention to stability already when developing a recipe. As the vitamin C in a serum gradually breaks down, the look of the product changes too: a typical signal is a yellowing to browning of the originally pale liquid, and sometimes a change of scent. If you notice such a colour change in your serum, it is a sign that it is worth reaching for a new pack. This is why studies on the stability of vitamin C in cosmetic products (source: the PubMed database) focus mainly on packaging, pH and the presence of other ingredients that slow the breakdown. Dark glass, a pump instead of an open jar, and storage away from heat and direct sun are simple steps that extend the life of the serum.
How to add a vitamin C serum to your routine
A serum like this is most often placed in the morning routine, right after toning and before the cream, because during the day it supports care for an even skin tone. Some women prefer it in the evening, especially if they have more sensitive skin and prefer a lighter product without further active ingredients during the day. It is important to apply it to dry skin and wait a few minutes for it to absorb before moving on to the next step of your routine. If you are just putting your routine together and have not used a similar serum so far, start by applying it every other day to see how your skin reacts to the new ingredient, and only gradually move to daily use, depending on what suits you.
| Step | Morning | Evening |
|---|---|---|
| 1. Cleansing | Gentle cleansing gel | Thorough make-up removal and cleansing |
| 2. Toning | Facial toner | Facial toner |
| 3. Serum | This brightening serum | Another serum as needed |
| 4. Care | Light day cream, protect your skin from the sun during the day | A richer night cream |
What to combine a vitamin C serum with
This ingredient pairs well with hyaluronic acid, which adds a feeling of hydration to the skin and softens any tightness; you will find more about it in the article on hyaluronic acid. On the other hand, when combining it with stronger exfoliating acids, such as salicylic acid, or with retinol, it is worth proceeding carefully and spreading the individual steps between morning and evening, or between different days of the week. The reason is not that your skin would necessarily be harmed by such a combination, but rather that several strong active ingredients at once can interfere with one another or put unnecessary strain on more sensitive skin. A detailed overview of which ingredients get in each other's way in a routine and why can be found in the article The art of layering. If you are not sure how exactly to put a routine together for your skin, our Advisor will help you.
What to watch out for
When using a new vitamin C serum for the first time, always try a smaller amount, ideally on a small area of skin, and wait a day to see how your skin reacts. More sensitive skin may react to the lower pH of L-ascorbic acid with a slight tingling; in that case it is worth reaching for a serum with a gentler vitamin C derivative. Always close the bottle straight after use to limit contact of the contents with air, and store the serum away from heat and direct sun. If the colour or scent of the serum changes markedly compared with when you bought it, it is a signal that it is worth reaching for a new pack instead of topping up the old one.
Did you know…
Did you know that a vitamin C serum turning yellow is not a manufacturing defect, but a common sign that this sensitive ingredient is gradually breaking down under the influence of light, heat or air?