How Does Medik8 C-Tetra Serum Compare To The Other Vitamin C Products From Medik8?

Last Updated on August 26, 2026 by Giorgia Guazzarotti

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, my preference is Tetrahexyldecyl Ascorbate, the derivative used in Medik8 C-Tetra Serum. It’s sort of the gold standard of derivatives, if you ask me. Here’s why:

What’s In Medik8 C-Tetra Serum?

TETRAHEXYLDECYL ASCORBATE TO BRIGHTEN SKIN

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. Is a powerful antioxidant that 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 in the list of ingredients. 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

JOJOBA OIL TO MOISTURISE SKIN

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?

GRAPEFRUIT PEEL OIL TO… IRRITATE 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):

The Rest Of The Formula & Ingredients

• Cyclopentasiloxane: A volatile silicone that creates a velvety texture that glides smoothly on the skin – and then evaporates into thin air.
• Cyclohexasiloxane: Another silicones that creates soft, smooth texture that don’t feel greasy or sticky. It evaporates quickly after application.
• Tocopheryl Acetate: A form of Vitamin E that fights free radicals and helps Vitamin C last longer.
• Limonene: A fragrant component of citrus fruits, it makes the product smell good. But it must be listed separately on the label because it’s a common allergen.
• PPG-12/SMDI Copolymer: It has fixative properties that keep active ingredients suspended and helps make skin softer and smoother.
• Citral: Another component of grapefruit oil that smells like lemon. It too must be listed separately on the label because it’s a common allergen.
• Linalool: It has a spicy floral scent that makes the serum good. But it’s another common allergen.
• Geraniol: Another fragrant ingredient that smells good, but can irritate sensitive skin.

Texture

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

Fragrance

Technically, it’s fragrance-free. Medik8 didn’t add any separate fragrance to it. Fragrance can irritate skin, so it’s always good to leave it out. But then, you may have a product that does an amazing job at preventing wrinkles, but you don’t want to use it cos it smells like crap.

The workaround? Medik8 added grapefruit oil, an essential oil that gives the serum a subtly summery citrus scent. But, the fragrant components that make this oil smell amazing can also irritate sensitive skin.

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. The closer to clean skin you apply it, the easier it penetrates skin and the better it works. It is gentle enough for daily use, even if this is your first use of Vitamin C. And, of course, always do a patch test first.

Packaging

The new version comes in a dark bottle with a dropper applicator for ease of use. Plus, it looks good on your vanity too.

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. One last thing: this form of Vitamin C should be safe during pregnancy too. But it’s always a good idea to double check with your doctor, just in case.

How Does Medik8 C-Tetra Serum Compare To The Other Vitamin C Products From Medik8?

Medik8 C-Tetra Serum isn’t the only Vitamin C product Medik8 makes. Here’s a quick guide to let you know if this is the best option for you or if you’d be better off with one of its siblings:

• Medik8 Daily Radiance Vitamin C™ (£62.00): A lightweight cream with Tetrahexyldecyl Ascorbate to moisturise, brighten, and fight wrinkles at the same time. It’s best for combination skin. Available at Cult Beauty, Look Fantastic, Medik8, Sephora, and SpaceNK
• Medik8 R-Retinoate® Day & Night (£149.00): It has a retinoid ester and Tetrahexyldecyl Ascorbate (Vitamin C derivative) to prevent and treat wrinkles. It’s a good option for people with sensitive skin that can’t tolerate retinol and/or L-Ascorbic Acid (the pure form of Vitamin C). Available at Medik8, Sephora, and SpaceNK
• Medik8 Super C Ferulic™ (£69.00): It has 30% 3-O-Ethyl Ascorbic Acid, a derivative of Vitamin C. I haven’t seen any independent proof it works better than L-Ascorbic Acid, the pure form of Vitamin C. But if you’re curious to try it, it can help prevent wrinkles. Available at Medik8, Sephora, and SpaceNK
• Medik8 C-Tetra Cream (£55.00): A hydrating cream with 7% Tetrahexyldecyl Ascorbate, Vitamin E, and hyaluronic acid. It’s best for combination skin. Available at Look Fantastic, Medik8, and Sephora
• Medik8 C-Tetra Eye (£24.00): It’s the same thing as Medik8 C-Tetra Serum, so save yourself some money and apply that on the eye area too.
• Medik8 C-Tetra Luxe (£62.00): It’s similar to Medik8 C-Tetra, but it has twice the amount of Vitamin C and an oilier base. If you have dry skin, this is more effective and more moisturising for you. Available at Medik8, Sephora, and SpaceNK

What I Like About Medik8 C-Tetra Serum

• Helps prevent wrinkles for youthful-looking skin
• Helps brighten skin tone
• Lightweight, fast-absorbing texture
• Doesn’t go bad as fast as L-Ascorbic Acid
• Practical packaging

What I DON’T Like About Medik8 C-Tetra Serum

• Fragrance may irritate sensitive skin
• Not as effective as 15% L-Ascorbic Acid, Vitamin E and Ferulic Acid

Who Should Use This?

Anyone who wants to prevent premature aging and can’t use L-Ascorbic Acid because it irritates their skin.

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

Price & Availability

£45.00 at Cult Beauty, Look Fantastic, Medik8, Sephora, and SpaceNK

The Verdict: Should You Buy 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.  I mean, there’s a reason why it’s one of the brand’s bestsellers and is standing the test of time.