Medik8 C-Tetra Serum with vitamin C and antioxidants 30ml

What is C-Tetra® and what makes it exceptional?

C-Tetra® is Medik8's flagship vitamin serum, formulated for people sensitive to classic vitamin C forms (L-ascorbic acid, which oxidises quickly and can irritate) and those beginning their vitamin C journey. Instead of unstable L-ascorbic acid, C-Tetra® uses tetrahexyldecyl ascorbate (THD) — a lipid, stabilised form of vitamin C that:

• is exceptionally stable — retains its potency for 12 months after opening, regardless of light and air exposure,
• is lipophilic — penetrates the skin's lipid barrier more efficiently than water-soluble forms of vitamin C, reaching deeper tissue layers,
• is remarkably gentle — does not acidify the skin, causes no tingling or redness typical of classic vitamin C forms.

The jojoba seed oil base provides light, non-occlusive nourishment — skin feels soft and relaxed without any greasy residue.

Key active ingredients

• 7% Tetrahexyldecyl Ascorbate (THD) — gentle, stabilised form of vitamin C with antioxidant, brightening and collagen-supporting properties. Exceptional 12-month post-opening stability.
• Vitamin E (tocopherol) — potent antioxidant synergistically amplifying vitamin C's action, providing additional protection against free radicals and photoageing.
• Jojoba seed oil — lightweight lipid base, biocompatible with skin, hydrating without heaviness.

Confirmed clinical results*

• 7 days to restored radiance and even skin tone,
• 7 days to visibly brighter and smoother skin,
• 96% of people with sensitive skin confirmed product gentleness,
• 87% of sensitive skin users — the gentlest vitamin C serum they have ever used,
• 90% of respondents — skin immediately softer after application,
• 4 weeks — visible reduction of wrinkles and pigmentation.

*Independent consumer study, 4 weeks, 52 people with sensitive skin.

Benefits

• Brightening of uneven skin tone and complexion,
• Pigmentation reduction and dullness,
• reduced visibility of fine lines and wrinkles,
• Antioxidant protection — free radical neutralisation, photoageing prevention,
• support for collagen synthesis,
• Nourishment and softening without greasiness,
• visible radiance and glow.

Who is C-Tetra® for?

• sensitive skin — reactive to classic vitamin C forms,
• starting with vitamin C — gentle introduction to the ingredient,
• dull, grey, lack-lustre skin,
• skin with uneven tone and pigmentation,
• skin with first signs of ageing.

How to use

• Time: morning, after cleansing.
• Amount: 4 drops warmed in the hands, then pressed into face, neck and décolletage.
• Order: after toner, before SPF moisturiser (e.g. Medik8 Advanced Day Ultimate Protect).
• Patch test: for sensitive skin — test 24 hours before first full facial application.
• Medik8 CSA Philosophy: C (vitamin C morning) → S (SPF morning) → A (vitamin A evening) = comprehensive anti-ageing approach.

Specifications and packaging

• Volume: 30 ml
• Vitamin C concentration: 7% (tetrahexyldecyl ascorbate)
• Texture: lightweight oil / lipid serum
• Skin type: sensitive, normal, combination
• Free from: artificial fragrances, synthetic dyes, parabens
• Certification: Vegan Society
• Manufacturer: Medik8 (UK) | EU Responsible Person: TRC 2514, AA, NL

The C-Tetra® range – find your level

• C-Tetra® 7% (this product) — lightweight oil, ideal vitamin C introduction, sensitive skin,
• C-Tetra® Luxe 14% — rich oil with squalane and passion fruit oil, dry skin needing more radiance,
• C-Tetra® Advanced 20% — lightweight gel-serum with plant exosomes and acetyl zingerone, skin with visible signs of ageing.

FAQ – questions and answers

How does tetrahexyldecyl ascorbate (THD) differ from classic vitamin C?

Classic vitamin C (L-ascorbic acid) is unstable — it oxidises in light, heat and air, loses efficacy and can irritate skin. THD (tetrahexyldecyl ascorbate) is a stable, lipophilic vitamin C form: it does not acidify skin, does not cause stinging, retains potency for 12 months post-opening and penetrates the skin's lipid barrier more efficiently. This is why C-Tetra® is safe even for sensitive skin.

Can I use C-Tetra® in summer?

Yes — vitamin C in the morning is a key element of skin protection. It acts as an antioxidant neutralising UV-generated free radicals, amplifying the effect of SPF protection. Always apply SPF after the serum has absorbed — this is the foundation of Medik8's CSA philosophy.

Will the serum make my skin feel greasy?

No — despite the lipid base, the formula is very lightweight. Jojoba seed oil is structurally close to human sebum and absorbs well, leaving no oily film. 90% of study participants felt skin immediately softer without any greasiness.

When should I choose C-Tetra® over C-Tetra® Luxe or Advanced?

C-Tetra® 7% is the ideal starting point — for sensitive, normal and combination skin new to vitamin C. C-Tetra Luxe (14%) suits dry skin needing richer nourishment. C-Tetra Advanced (20%) with plant exosomes is the choice for skin with pronounced signs of ageing requiring intensive regeneration.

• What is C-Tetra® and what makes it exceptional?
• Key active ingredients
• Confirmed clinical results
• Benefits
• Who is C-Tetra® for?
• How to use
• Specifications
• The C-Tetra® range
• FAQ