Medik8 C-Tetra Serum review

NOTE: This serum is now called Medik-8 C-Tetra and comes in a slightly different bottle. But the formula inside is the same, so everything still applies.

What’s the best Vitamin C derivative out there?

Yeah, yeah, ideally we should all use pure vitamin C (L-Ascorbic Acid). But that’s irritating as hell. Unstable AF. Goes bad before you reach half the bottle and stings your skin like crazy.

Give me a derivative, pronto!

But, which one? There are more than a dozen these days, all promising the same benefits as pure vitamin C without the side effects. How do you know which one really delivers?

Personally, I’m partial to Tetrahexyldecyl Ascorbate, the derivative used in Medik8 C-Tetra Serum. Here’s why:

What’s In Medik8 C-Tetra Serum?


Let’s be honest: Tetrahexyldecyl Ascorbate (TA) isn’t as powerful as L-Ascorbic Acid. But it does two things way better than it:

  1. Stability: It doesn’t oxidise (i.e. go bad) as quickly when exposed to light and air (read: you can actually finish the bottle!).
  2. Penetration: While L-Ascorbic Acid only penetrates the epidermis (uppermost layers of your skin), TA penetrates both the epidermis and the dermis (the deeper layer below it).

TA is so good at penetrating skin because it’s one of the few forms of vitamin C that’s oil-soluble. And that straight away catapults it to the top of the vitamin-C-derivates-to-try list.

But, what the heck does it do once it penetrates skin? Studies say it:

  1. Brightens the complexion
  2. Fights the free radicals that cause wrinkles
  3. Boost collagen production

The catch? These studies are done by using either high concentrations of TA (20%>) or by combining lower doses (8%>) with L-Ascorbic Acid.

Medik8 C-Tetra ONLY uses 7% Tetrahexyldecyl Ascorbate.

Don’t get me wrong. I’m not saying this concentration is too low to work (I did see an improvement, as I’ll share later on in this review).

But at this concentration, this is more of a preventative serum for women in their late 20s/early 30s. If you want to fade dark spots or reduce wrinkles, you’re still better off with L-Ascorbic Acid.

One more thing: vitamin C works better when used together with vitamin E and ferulic acid. This serum only has vitamin E. Not a biggie. It’ll still do its job well. I just wanted to mention it for those who are looking for all 3 antioxidants in their serum.

Related: Why You Should Add Vitamin C Into Your Skincare Routine

medik8 ce tetra vitamin c antioxidant serum


I know what you’re thinking: “I have oily skin so anything with oil is out of the question.”

Normally, you’d be right. But jojoba oil is one of the exceptions to the rule. Why?

Out of all the oils, jojoba oil resembles sebum (your skin’s natural moisturiser) more closely. This means it’s lightweight enough to sink quickly into your skin and not aggravate acne.

Plus – and this is good news for ALL skin types – jojoba oil is rich in fatty acids that moisturise skin and increase its moisture content. 

Translation: it moisturises skin without leaving a greasy, pimply mess behind.

Fun fact: jojoba is pronounced “ho-ho-ba”.

Related: What Are The Best Facial Oils For Oily Skin?


I’ll be brief. Grapefruit peel oil is here only to make the serum smell citrusy (because how else do you expect vitamin C to smell like?!).

Problem is, its fragrant components may irritate sensitive skin. There’s only a drop of it here, though, so it’s unlikely to be problematic for any other skin type.

I’ve been using it for weeks and I didn’t experience any irritations. Even though I still prefer my skincare fragrance-free, I have to admit I like how this serum smells. 🙂

Related: Is Fragrance In Skincare As Bad As Paula Begoun Says?

Struggling to put together a skincare routine that minimises wrinkles, prevents premature aging, and gives your complexion a youthful glow? Download your FREE “Best Anti-Aging Skincare Routine” to get started (it features product recommendations + right application order):


Lightweight texture that sinks into the skin really quickly. I swear you’d never say the base is an oil!


Subtly citrusy.

How To Use It

I like to use Vitamin C in the morning underneath sunscreen to maximise sun protection. But you can also use it at night before moisturiser.

Performance & Personal Opinion

Within a week of using Medik8 C-Tetra Serum, I noticed my skin becoming brighter. My skin has a lovely glow that makes it look healthy.

I can’t see that I’ve seen any reduction in fine lines, but then this serum is preventative. You use it to prevent wrinkles from creeping up on your face, not so much to reduce those that are already there.

And the science there is solid. Vitamins C&E can destroy free radicals before they leave wrinkles on your face. So I have no complaints here. I know that my skin is well protected all day long.

Who Is This For?

Anyone who wants to prevent premature aging and can’t/won’t use L-Ascorbic Acid.

Who Is This NOT For?

If you’re serious about anti-aging, L-Ascorbic Acid is still the best option.

medik8 ce tetra serum review


A dark bottle with a dropper applicator. It’s sleek and practical.

Does Medik8 C-Tetra Serum Live Up To Its Claims?

Utilising the antioxidant power of vitamin C and E, the hydrating serum brightens and smooths the complexion, while fighting free radicals to reduce visible signs of ageing. True.
The formula sinks into skin quickly, leaving behind a soft and glowing complexion. True.

Price & Availability

£35.00 at Cult Beauty, Feel Unique, Look Fantastic, and SpaceNK

Do You Need It?

If you’re looking for a gentle Vitamin C serum that doesn’t go bad within a few weeks, this is a good option to consider.

Dupes & Alternatives


Simmondsia Chinensis (Jojoba) Seed Oil, Cyclopentasiloxane, Cyclohexasiloxane, Tetrahexyldecyl Ascorbate, Tocopheryl Acetate, PPG-12/SMDI Copolymer, Citrus Grandis (Grapefruit) Peel Oil, Limonene