Medik8 C-Tetra vs Super C Ferulic: Which Vitamin C Serum Should You Choose?
Updated Aug 20, 2026
The Verdict
C-Tetra and Super C Ferulic aren't really competing for the same shopper. C-Tetra is Medik8's gentle, 7% lipid-soluble entry point, built for vitamin C beginners and sensitive skin. Super C Ferulic is the brand's strongest vitamin C serum, a 30% ethylated ascorbic acid formula for mature or experienced skin that already tolerates vitamin C well — and Medik8 is explicit that it is not the one to reach for if your skin is sensitive.
C-Tetra and Super C Ferulic are Medik8's gentlest and strongest vitamin C serums. C-Tetra is built on 7% Tetrahexyldecyl Ascorbate, a lipid-soluble, sensitive-friendly ester, in a light oil base. Super C Ferulic uses 30% Ethylated L-Ascorbic Acid with ferulic acid and vitamin E — Medik8's most potent vitamin C formula, and one the brand states is not recommended for sensitive skin.
Quick facts
| C-Tetra | Super C Ferulic | |
|---|---|---|
| Vitamin C form | 7% Tetrahexyldecyl Ascorbate (lipid-soluble ester) | 30% Ethylated L-Ascorbic Acid |
| Supporting actives | Vitamin E, jojoba seed oil base | Ferulic Acid, Vitamin E, Turmeric Root Extract |
| Texture | Silky, oil-based serum | Lightweight, dry-touch serum |
| Sensitivity | Medik8's gentlest vitamin C serum; formulated for sensitive skin | Not recommended for sensitive skin, per Medik8 |
| Best suited to | Vitamin C beginners, sensitive or reactive skin, all skin types wanting a low-risk daily antioxidant | Mature or sun-damaged skin, experienced vitamin C users wanting maximum strength |
| Size | 30ml | 30ml |
| Price band | £40s | £60s |
The core difference: a gentle ester vs a high-strength acid
The two formulas take genuinely different approaches to delivering vitamin C, not just different strengths of the same ingredient. C-Tetra is built around Tetrahexyldecyl Ascorbate at 7%, a fat-soluble ester derivative of vitamin C. It sits comfortably in an oil base, resists oxidation for longer than traditional ascorbic acid, and is generally considered gentler on the skin barrier — which is exactly why Medik8 positions it as the brand's entry point.
Super C Ferulic takes the opposite route: 30% Ethylated L-Ascorbic Acid, a stabilised but still high-strength, acid-based form of vitamin C, paired with ferulic acid and vitamin E in the classic antioxidant-trio formulation. Ethylation is what Medik8 uses to keep this form of vitamin C stable over the life of the bottle, but it doesn't change the fact that a 30% acid-based vitamin C is a considerably more concentrated, higher-potency product than a 7% oil-soluble ester. That difference in both concentration and chemical form is the reason one is marketed as gentle and the other explicitly isn't.
Why Super C Ferulic isn't recommended for sensitive skin
Medik8's own product guidance for Super C Ferulic states, in its own words, that it is "not recommended for sensitive skin types due to high potency", and directs sensitive-skin shoppers towards C-Tetra instead. That's a meaningful distinction worth taking at face value rather than working around: a warming or tingling sensation on application is described as normal for Super C Ferulic and should settle within seconds, but if your skin reacts easily, runs sensitive, or you've had trouble with ascorbic acid serums before, this isn't the vitamin C serum to start with.
C-Tetra sits at the other end of that same spectrum. Medik8 markets it as the gentlest vitamin C serum in its range, formulated specifically with sensitive and first-time users in mind, thanks to the lipid-soluble ester form and the absence of the sting associated with higher-strength acid formulas.
Side-by-side comparison
| C-Tetra | Super C Ferulic | |
|---|---|---|
| Formulated for | Vitamin C beginners; sensitive, reactive or first-time skin; all skin types wanting a low-risk daily antioxidant | Mature, normal to dry skin with visible sun damage, dark spots or uneven tone; experienced vitamin C users |
| Base | Jojoba seed oil, lightweight and non-greasy | Water-light, fast-absorbing, dry-touch |
| Scent | Light citrus note from grapefruit peel oil | Not specified on the product page |
| Where it sits in the range | Entry point, below C-Tetra Luxe and Super C Ferulic | Top of the range — Medik8's most concentrated vitamin C serum |
| Not ideal for | Those wanting maximum antioxidant strength once skin has adjusted to vitamin C | Sensitive skin, or anyone trying vitamin C for the first time |
Texture and how each wears through the day
C-Tetra has a silky, oil-based texture that absorbs without sitting greasy, and layers reasonably well under moisturiser and SPF once a small amount has been worked in. Super C Ferulic is the opposite feel: a lightweight, fast-absorbing, dry-touch serum with a water-light consistency designed to sink in quickly without pilling under the next steps in a morning routine. Neither is heavy or difficult to layer — the difference is more about finish (a light residual sheen with C-Tetra's oil base versus a genuinely dry finish with Super C Ferulic) than about how easily either sits under sunscreen.
Can you move from C-Tetra to Super C Ferulic?
Yes, and it's a reasonably common progression within the Medik8 range — start on C-Tetra (or the richer C-Tetra Luxe) to let skin build tolerance to daily vitamin C, then step up to Super C Ferulic once you know your skin handles the ingredient well and you're after a more potent, higher-strength formula. It isn't a straight swap, though: Super C Ferulic's 30% ethylated ascorbic acid is a meaningfully stronger, more acid-forward formula than C-Tetra's 7% ester, so moving up is worth doing gradually rather than switching bottles outright, and isn't the right move at all if your skin is sensitive or reactive. If you're not sure whether your skin is ready to step up, our team can advise based on your skin history — contact us before making the switch.
Where these fit in the wider Medik8 vitamin C range
C-Tetra and Super C Ferulic are the two clearest end-points in Medik8's vitamin C line-up, but they're not the only options. Daily Radiance Vitamin C combines a lighter vitamin C dose with SPF for anyone who wants their morning antioxidant and sun protection in one step, and C-Tetra Luxe offers a richer, more indulgent version of C-Tetra's gentle technology for those who want a step up in sensorial feel without moving to a stronger acid. For the full picture across the range, see our guide to the best Medik8 vitamin C serums, or browse the Medik8 brand hub.
Our verdict
This isn't really a head-to-head between two similar products — it's a comparison of Medik8's most cautious and most concentrated vitamin C options, and the right choice depends almost entirely on how your skin handles vitamin C already. If you're new to it, have sensitive or reactive skin, or you've been caught out by a stinging ascorbic acid serum before, C-Tetra's 7% lipid-soluble formula is the sensible, low-risk starting point. If your skin already tolerates vitamin C comfortably and you're chasing a more potent, higher-strength antioxidant step, Super C Ferulic's 30% ethylated ascorbic acid, ferulic acid and vitamin E combination is Medik8's answer — just not, by the brand's own guidance, if your skin is sensitive.
If you're pregnant or breastfeeding, please contact our team for advice before use.