5 minute read
Vitamin C is one of the few skincare ingredients almost everyone agrees on. Where brands differ sharply is which form of it they use, and that decision has real consequences for how a serum feels, how it should be stored and who it suits.
SkinCeuticals and Medik8 sit at opposite ends of that decision, which makes them a genuinely useful comparison.
The SkinCeuticals Approach: Pure L-Ascorbic Acid
SkinCeuticals builds around pure vitamin C in the form of L-ascorbic acid. This is the most studied form of the ingredient and the benchmark against which others are measured, but it is also water-soluble, low pH and prone to oxidising over time.
C E Ferulic is the best known example, combining vitamin C with vitamin E and ferulic acid to deliver antioxidant protection and improve the look of fine lines. Our full guide on how to use SkinCeuticals C E Ferulic goes into more detail.
Phloretin CF takes the same principle in a different direction, pairing 10% pure vitamin C with 2% phloretin and 0.5% ferulic acid. It leans more towards uneven tone and discolouration, and suits normal to oily skin. There is also a gel version if you prefer a lighter texture.
The Medik8 Approach: Oil-Soluble Vitamin C
Medik8 uses tetrahexyldecyl ascorbate, an oil-soluble derivative of vitamin C. It is more stable than L-ascorbic acid, sits at a skin-friendly pH and penetrates through the skin's lipid layers, which generally means less tingling and less risk of irritation.
C-Tetra is the original, at 7%, and is positioned as an introduction to vitamin C. C-Tetra Luxe doubles that to 14% in a richer base, and C-Tetra Advanced goes to 20% for accelerated brightening.
Which Is Better For Sensitive Skin?
Medik8, in most cases. Pure L-ascorbic acid formulations need a low pH to remain effective, and that acidity is what causes the brief tingle many people notice with C E Ferulic. Oil-soluble vitamin C avoids that entirely.
If you have tried a pure vitamin C serum and found it stung or left your skin flushed, moving to C-Tetra rather than abandoning vitamin C altogether is usually the answer.
Which Is Better For Pigmentation And Uneven Tone?
This is where SkinCeuticals has the edge, and Phloretin CF in particular. The combination of pure vitamin C with phloretin and ferulic acid is specifically formulated around discolouration rather than general antioxidant defence.
If pigmentation is your primary concern, it is also worth looking at SkinCeuticals Discolouration Defense, which can be layered alongside a vitamin C serum. Our guide on how to get rid of hyperpigmentation covers the wider routine.
Which Is Better For Dry Versus Oily Skin?
C E Ferulic and C-Tetra Luxe both have richer textures that suit normal to dry skin. Phloretin CF and the original C-Tetra are lighter and better suited to normal to oily or combination skin.
Texture matters more than people expect with vitamin C, because these are products you should be using every single morning. A serum that feels wrong on your skin is a serum you will stop using.
Which Should You Choose If You Are New To Vitamin C?
Start with the original C-Tetra. It is the gentlest introduction, the most forgiving on storage, and it lets you establish whether vitamin C suits your skin before committing to a higher-priced serum.
If you already know you tolerate actives well and you want the most studied option available, C E Ferulic is the obvious choice.
Can You Use Both?
There is little point using two vitamin C serums at the same time in the same routine, and doing so increases the chance of irritation without adding much benefit.
What does work well is using one form seasonally. Some people prefer a pure vitamin C serum through autumn and winter, then switch to an oil-soluble version in summer when skin is more heat-stressed and reactive.
How Should You Store Vitamin C?
Pure L-ascorbic acid oxidises on exposure to light, air and heat, and darkens from pale straw to amber as it does. Keep SkinCeuticals serums tightly closed, away from windowsills and out of the bathroom if it gets steamy. A serum that has turned deep brown has lost potency.
Medik8's oil-soluble formulations are considerably more stable and far less fussy about storage, which is a genuine practical advantage.
When Should You Apply Vitamin C?
In the morning, after cleansing and before moisturiser and SPF. Vitamin C is primarily an antioxidant, so it does its most useful work during the day when your skin is exposed to UV and pollution.
Pair it with a retinoid at night rather than in the same routine. Our article on retinol versus vitamin C explains how the two fit together across the day.