Ferulic acid in skincare: what the vitamin C stabiliser really does and when you can skip it
ACTIVE INGREDIENTS
Ferulic acid is a plant antioxidant with one main job in skincare: keeping pure L-ascorbic acid (vitamin C) and vitamin E stable in a serum for longer. In a laboratory study on pig skin, adding it also doubled the protection this combination gave against simulated sunlight. On its own, ferulic acid has only thin evidence behind it. If your vitamin C already comes in a stable form, it is a possible extra, not a must. And it never replaces sunscreen.
What is ferulic acid and where does it come from?
Ferulic acid is a plant compound from the hydroxycinnamic acid group that is found in the cell walls of a great many plants, especially cereals such as rice and wheat, but also in fruit and vegetables. Plants use it as a building block for their cell walls and as protection against light and oxidative stress. The Duke University research team behind the best-known study on ferulic acid in serums describes it in the Journal of Investigative Dermatology as a potent antioxidant that is ubiquitous in plants. Chemically, it is closely related to caffeic acid, but slightly more fat-soluble. A 2018 review in Skin Pharmacology and Physiology notes that ferulic acid has low toxicity and is widely used in the pharmaceutical, food and cosmetics industries.
The same review also names the weakness that matters most for your skincare: ferulic acid itself tends to oxidise quickly. So it is not an indestructible shield but an antioxidant that gets used up in the formula while it protects other ingredients. That is exactly why it almost never appears on its own, but as part of a blend with vitamin C and vitamin E. Other plant antioxidants such as resveratrol or green tea extract are used in serums in a similar way, but they are separate substances with their own body of evidence.
How does ferulic acid stabilise vitamin C, and why L-ascorbic acid in particular?
Ferulic acid stabilises vitamin C by acting as an additional antioxidant in the formula, which slows down the oxidative breakdown of delicate L-ascorbic acid. In a water-based solution, pure L-ascorbic acid is the classic, well-studied form of vitamin C, but also the least stable: air, light and heat oxidise it, and the serum discolours and loses its effect. This is precisely where the study that almost every ferulic acid serum refers to comes in. In 2005, Lin and colleagues added ferulic acid to a solution of 15% L-ascorbic acid and 1% alpha-tocopherol (vitamin E). According to the paper in the Journal of Investigative Dermatology, this improved the chemical stability of both vitamins, and the skin’s protection against simulated sunlight rose from about fourfold to about eightfold, measured by redness and sunburn cells. The tests, however, were carried out on pig skin. Why vitamins C and E work together in the first place is a topic of its own, covered in the article on combining vitamin C and vitamin E.
In 2008, a study on human skin followed in the Journal of the American Academy of Dermatology: a solution of 15% L-ascorbic acid, 1% alpha-tocopherol and 0.5% ferulic acid was applied to patches of skin for four days and afterwards provided measurable protection against UV damage. The authors themselves point out as a limitation that relatively few people were studied. Both papers come from the same research group led by Sheldon Pinnell. That does not make the results wrong, but it is a reason to read them as a strong indication rather than final proof. And they apply to pure L-ascorbic acid – the very case in which a stabiliser has the most work to do.
What does ferulic acid do for skin without vitamin C?
Without vitamin C, ferulic acid is an antioxidant in its own right with some positive findings, but with far thinner evidence than in the combination. A study published in the International Journal of Pharmaceutics in 2000 first showed in the laboratory, on excised human skin, that ferulic acid can penetrate the outermost layer of the skin, and more readily than the related caffeic acid. In the second part, healthy volunteers applied a saturated water-based ferulic acid solution, which then significantly reduced UVB-induced redness. That is a genuine protective effect measured in people, but with a plain test solution rather than a finished cosmetic product.
The review in Skin Pharmacology and Physiology lists further possible roles, such as protecting skin cells, collagen and elastin and inhibiting melanin production. That sounds promising, but it is based on very different kinds of studies, and how much of it reaches your skin from a finished cream is an open question. So you should not expect any visible change in pigmentation or wrinkles from ferulic acid. If you have melasma or patches that are changing, they need to be checked by a dermatologist, not handled from the bathroom shelf.
How do you spot ferulic acid on the INCI list, and what amounts are typical?
On the INCI list, ferulic acid appears as “Ferulic Acid”, usually far down, because it is used in small amounts. The formula that the Duke group tested on human skin in 2008 contained 0.5% ferulic acid alongside 15% L-ascorbic acid and 1% alpha-tocopherol. If a brand states a percentage for its product, you can measure it against this figure. Many brands give no amount at all, though, which leaves you with only its position on the list. Ingredients below one per cent may be listed at the end in any order, so their position says little there. How to decode lists like this in general is explained in the article on how to read an ingredient list.
When you are deciding what to buy, the overall combination matters more than ferulic acid alone. Before you buy a serum because of its ferulic acid, a quick check is worth it:
- Which form of vitamin C is on the list: Ascorbic Acid (pure L-ascorbic acid) or a derivative such as 3-O-Ethyl Ascorbic Acid?
- Does it also contain Tocopherol (vitamin E), as in the combination that was studied?
- Is the packaging protected from light and as airtight as possible, such as a dark bottle or an airless pump?
- Does the brand state the vitamin C concentration, or only “with vitamin C”?
How much L-ascorbic acid makes sense alongside it is a separate question. The article on it explains which vitamin C concentration actually makes sense.
Is ferulic acid suitable for sensitive skin?
Ferulic acid itself is considered well tolerated, and the 2018 review describes its toxicity as low. If a ferulic acid serum still burns or tingles, it is usually not the ferulic acid but its surroundings: pure L-ascorbic acid needs an acidic pH to stay stable and be absorbed, and that acidity is exactly what sensitive skin feels. Depending on the product, high vitamin C concentrations, alcohol or fragrance may also be in the same formula. If your skin is sensitive, it is therefore worth looking at the whole ingredient list rather than just the active ingredient on the front of the pack.
As with any ingredient, an individual intolerance is always possible. If the serum also contains vitamin E, the article on what vitamin E does for skin also covers how well it is generally tolerated. If you have rosacea, eczema or very red skin, talk to a dermatologist before starting new acidic serums rather than testing your way through several products.
Test a new ferulic acid serum on a small area, such as along the jawline, for a few evenings before applying it to your whole face. A slight tingle in the first few seconds is common with acidic vitamin C serums; lasting burning or redness is a reason to stop.
Do you need ferulic acid if your vitamin C is already stable?
No, if your vitamin C already comes in a stable form, you do not need ferulic acid on top. Its proven main benefit is protecting pure L-ascorbic acid in a water-based solution from breaking down quickly. If the form of vitamin C has already solved that problem, its most important job disappears. To be honest, though, this also means that the combination with ferulic acid has not been studied comparably for derivatives such as 3-O-Ethyl Ascorbic Acid, and overall there is less data than for L-ascorbic acid. You can find out more about 3-O-Ethyl Ascorbic Acid, the stable form of vitamin C, and how to spot a stable vitamin C serum in separate articles.
| Your vitamin C | Is ferulic acid worth it? | Why |
|---|---|---|
| Pure L-ascorbic acid in a water-based serum | Yes | This is exactly the combination that was studied, and it is where vitamin C breaks down fastest |
| L-ascorbic acid as a powder or in a water-free base | Unclear | Without water, vitamin C is more stable; there is no data on this variant with ferulic acid |
| Stable derivative such as 3-O-Ethyl Ascorbic Acid | Not needed | The stability comes from the form; the combination with ferulic acid has hardly been studied |
| No vitamin C | Optional | An antioxidant in its own right, with few studies in humans |
In our own routine, we solved this question through the form: The Duo contains 2% vitamin C as 3-O-Ethyl Ascorbic Acid, plus vitamin E (Tocopherol). Ferulic acid is not on the INCI list. That does not mean the Duo shares the study results of the vitamin C, E and ferulic acid solution that was tested – only that this form of vitamin C was not designed to need the stabiliser.
For vitamin C, I chose the stable 3-O-Ethyl form rather than pure L-ascorbic acid with a cocktail of stabilisers. That is why there is no ferulic acid in The Duo. It mattered more to me that the vitamin C comes in a form that does not need additives to rescue it. I don’t want to gloss over anything here: the well-known ferulic acid figures come from studies with L-ascorbic acid, and there is less data overall for 3-O-Ethyl Ascorbic Acid. So the Duo cannot point to those studies. It also has no SPF, which is why a separate sunscreen belongs on top in the morning. You can see which active ingredients it contains and in what concentrations in the overview of our active ingredients with their concentrations.
Frequently asked questions
Is ferulic acid an exfoliant?
No, ferulic acid is not an exfoliant. It belongs to the hydroxycinnamic acids, not to the fruit acids such as glycolic or lactic acid that loosen dead skin cells. If a ferulic acid serum tingles, that usually comes from the acidic pH of the vitamin C formula. So a serum like this does not replace an exfoliant. If your skin is sensitive, though, you should not layer an acidic vitamin C serum and an acid exfoliant on the same evening.
Morning or evening: when should I apply ferulic acid?
Morning is the obvious time, because the studies looked at protection when the solution was on the skin before UV exposure. Apply the serum after cleansing and finish with sunscreen. Using it in the evening does no harm, but no particular benefit has been shown for it. How often to apply it depends on the instructions for the specific product.
Does ferulic acid replace sunscreen?
No. The authors of the 2008 study write themselves that the combination works differently from sunscreens and is meant to supplement them, not replace them. Antioxidants do not filter UV light. During the day, you still need sunscreen for your face, applied generously as the last step.
Why does my ferulic acid serum smell or change colour?
A change from pale yellow towards orange or brown usually shows that the vitamin C is oxidising. Ferulic acid itself also tends to oxidise. A noticeably darker serum is less effective and should be replaced. A faint smell of its own can come from the raw materials, but if the serum smells noticeably different from when you opened it, that is a reason to stop using it.
Can I combine ferulic acid with niacinamide?
Yes, from an ingredient point of view there is nothing against combining ferulic acid and niacinamide. If your skin burns with a ferulic acid serum containing L-ascorbic acid, that is more likely due to the acidic pH than to the combination. In that case, it helps to use the two products at different times, such as vitamin C in the morning and niacinamide in the evening.
Is ferulic acid natural or synthetic?
Both exist. Ferulic acid can be extracted from plant material such as rice or made chemically, and in both cases the INCI list says “Ferulic Acid”. The molecule is the same. Whether a product discloses its origin depends on the brand, and it makes little difference to how well your skin tolerates it.
Do I need a ferulic acid serum if I use The Duo?
No, you do not need an additional ferulic acid serum. The Duo contains 2% vitamin C as stable 3-O-Ethyl Ascorbic Acid and vitamin E, but no ferulic acid. If you deliberately want a classic L-ascorbic acid serum with ferulic acid, that is a separate decision. It is not necessary; sunscreen in the morning matters more.
Sources
- Lin FH, Lin JY, Gupta RD, Tournas JA, Burch JA, Selim MA, et al. Ferulic acid stabilizes a solution of vitamins C and E and doubles its photoprotection of skin. Journal of Investigative Dermatology, 2005. Source
- Murray JC, Burch JA, Streilein RD, Iannacchione MA, Hall RP, Pinnell SR. A topical antioxidant solution containing vitamins C and E stabilized by ferulic acid provides protection for human skin against damage caused by ultraviolet irradiation. Journal of the American Academy of Dermatology, 2008. Source
- Saija A, Tomaino A, Trombetta D, De Pasquale A, Uccella N, Barbuzzi T, et al. In vitro and in vivo evaluation of caffeic and ferulic acids as topical photoprotective agents. International Journal of Pharmaceutics, 2000. Source
- Zduńska K, Dana A, Kolodziejczak A, Rotsztejn H. Antioxidant Properties of Ferulic Acid and Its Possible Application. Skin Pharmacology and Physiology, 2018. Source
