Vitamin C serum: why the form and formula matter

A vitamin C percentage tells you something about a serum, but it does not tell you everything. The ingredient's chemical form, the liquid carrying it and the way the finished product is tested all matter. Two bottles labelled with the same percentage need not behave alike.

For anyone comparing a vitamin C serum in Singapore, the ingredient list is a useful starting point. Reading it alongside the research helps separate what is known about vitamin C from what has actually been demonstrated for a particular product.

What vitamin C does in skin

Vitamin C is part of the skin's antioxidant defences. It can neutralise oxidants associated with ultraviolet exposure and environmental pollutants. A 2017 review by Pullar, Carr and Vissers describes this biology, while noting gaps in the evidence for topical products. A biological role is a reason to investigate an ingredient, not proof that every serum containing it delivers the same benefit. [1]

Vitamin C also has a role in research on pigment formation. Melanin production involves an enzyme called tyrosinase. The review discusses how vitamin C may reduce chemical intermediates generated during this process; research on certain derivatives has also found reduced melanin synthesis. This is more nuanced than saying every vitamin C ingredient simply switches tyrosinase off. [1]

These findings help explain interest in vitamin C for uneven-looking tone. They do not establish how much a particular serum will change someone's complexion, or how quickly.

L-ascorbic acid and formulation

L-ascorbic acid is the form commonly referred to as pure vitamin C. Its formulation presents challenges: it can oxidise, and delivery through the skin's outer barrier depends on the conditions in which it is applied. The 2017 review describes research in which acidic conditions supported topical delivery. [1]

That does not mean an acidic serum will irritate everyone, or that every derivative will feel more comfortable. Tolerance belongs to the whole formula and the person using it. An ingredient name cannot guarantee a particular skin response.

Nor does oxidation research justify saying that most vitamin C serums fail. Stability needs to be assessed in the finished formula, with its packaging and intended storage conditions. An ingredient's reputation cannot replace that testing.

What ethyl ascorbic acid research tells us

3-O-Ethyl Ascorbic Acid is a vitamin C derivative with an ethyl group attached at the 3-O position. This changes its chemical properties. Researchers have investigated it as an approach to the stability and delivery challenges associated with ascorbic acid. [2]

In a 2019 study, Iliopoulos and colleagues characterised the molecule and investigated its stability in selected solvents. They also measured delivery using full-thickness porcine skin in laboratory diffusion cells. Some solvents allowed the derivative to enter and pass through the skin; others produced skin uptake without measurable passage through it, or no detectable penetration. [2]

The practical lesson is that the vehicle, the liquid carrying the ingredient, matters. The experiment was not a clinical trial showing improved facial appearance, superior tolerance or equivalence to L-ascorbic acid. It did not test RADIANT-C MD SERUM. It also does not establish how much of this derivative is converted into ascorbic acid in a person using that serum.

How to read a 12% label

The current SW1 Shop listing names RADIANT-C MD SERUM as "12% Vitamin C". Its ingredient list identifies 3-O-Ethyl Ascorbic Acid and also lists tocopherol, ferulic acid and sodium hyaluronate. [4]

Keep the label percentage and the ingredient identity together. The listing does not demonstrate that its 12% claim is equivalent to 12% L-ascorbic acid in delivery or effect. These are different molecules, and evidence from one formulation cannot settle the performance of another.

There is no universal optimal percentage established by the sources discussed here. The 2019 study was designed to investigate chemical properties and delivery, not to identify an ideal consumer dose. A concentration claim alone cannot establish either effectiveness or daily tolerability. [2]

The same caution applies to pH. The current listing does not state a measured finished-product pH. Citric acid and sodium hydroxide appear in the ingredient list, but their presence does not reveal that value. Describing the serum as guaranteed neutral-pH would go beyond the information supplied. [4]

Vitamin C, vitamin E and ferulic acid

Tocopherol is a form of vitamin E. Vitamin C and vitamin E participate in an antioxidant network: the 2017 review describes vitamin C helping regenerate oxidised vitamin E, a lipid-soluble antioxidant. This is not the same as claiming that tocopherol continuously replenishes vitamin C in any serum containing both. [1]

Ferulic acid has been studied with these ingredients in a defined formulation. In a 2005 paper, Lin and colleagues investigated adding 0.5% ferulic acid to a solution containing 15% L-ascorbic acid and 1% alpha-tocopherol. They reported improved chemical stability and protection against experimental ultraviolet exposure for that tested system. [3]

Those results belong to that formula and experimental setting. RADIANT-C MD SERUM lists a vitamin C derivative, and its current page does not state the concentrations of tocopherol or ferulic acid. The shared ingredient names do not establish equivalent protection, a particular antioxidant regeneration cycle or an all-day effect. [4]

A straightforward morning routine

The current product directions are to apply a few drops to cleansed skin each morning, before moisturiser and SPF. Follow the packaging directions if they provide further instructions. [4]

There is no need to invent a precise waiting interval from the ingredient list. Allow the product to settle enough for comfortable layering, then continue with your routine. Introducing one new product at a time also makes it easier to notice which product coincides with discomfort.

Vitamin C serum is not sunscreen. Experimental antioxidant findings do not give an untested serum an SPF rating or justify reducing sun protection. Keep sunscreen in the routine rather than treating the antioxidant step as a substitute. [3]

If a product causes persistent irritation, stop using it and seek advice. A derivative label should never be read as a promise that irritation cannot occur.

Read the formula before choosing

A useful product page identifies the vitamin C form, gives directions and makes clear which claims are supported by testing. A percentage can help describe a formula, but it cannot stand in for evidence about delivery, stability or results.

View SKN THRPY RADIANT-C MD SERUM and its current ingredient list to review the 12% Vitamin C label and morning-use directions before deciding whether it belongs in your routine.

Sources

1. Pullar JM, Carr AC, Vissers MCM. The Roles of Vitamin C in Skin Health. Nutrients. 2017;9(8):866. https://pmc.ncbi.nlm.nih.gov/articles/PMC5579659/
2. Iliopoulos F, Sil BC, Moore DJ, Lucas RA, Lane ME. 3-O-ethyl-l-ascorbic acid: Characterisation and investigation of single solvent systems for delivery to the skin. International Journal of Pharmaceutics: X. 2019;1:100025. https://pmc.ncbi.nlm.nih.gov/articles/PMC6733298/
3. Lin JY et al. Ferulic Acid Stabilizes a Solution of Vitamins C and E and Doubles its Photoprotection of Skin. Journal of Investigative Dermatology. 2005;125(4):826-832. https://www.jidonline.org/article/S0022-202X(15)32491-X/fulltext
4. SW1 Shop. RADIANT-C MD SERUM 12% Vitamin C. Current product title, INCI and use directions checked live on 8 October 2026. https://sw1shop.com/products/radiant-c-md-serum

Shop the products

• RADIANT-C MD 12% Vitamin C — stabilised vitamin C at a declared 12%, with ferulic acid.
• GLOWGENIC C+T — vitamin C with niacinamide, licorice root and turmeric.
• PLASMABRIGHT TX-K — tranexamic acid, kojic acid and vitamin C on pigment.

Free delivery within Singapore on orders of S$100 and above.