Medik8 C-Tetra 30ml

Medik8's cult vitamin C serum, and the easiest place to start with the ingredient. C-Tetra uses 7% tetrahexyldecyl ascorbate - an oil-soluble, stabilised form of vitamin C that does not sting or oxidise the way L-ascorbic acid can - so it suits sensitive skin as well as beginners.

Applied each morning, it visibly brightens uneven tone, softens the look of fine lines and provides antioxidant defence against the free radicals behind premature ageing. Vitamin E boosts that protection, and a jojoba oil base keeps the texture light and non-greasy.

Oil-solubility is the reason this formula behaves so differently to a traditional vitamin C. It penetrates readily, stays stable in the bottle and does not need a low pH, which is what removes the tingle and the oxidation problem.

If dullness and uneven tone are your concerns and previous vitamin C serums have irritated, this is the one to try. If you want more strength later, C-Tetra Luxe and C-Tetra Advanced step it up.

Apply four to six drops to a cleansed face and neck in the morning, then follow with moisturiser and SPF.

In Medik8's CSA routine, C-Tetra is the C. Pair it with Advanced Day Total Protect or Advanced Day Ultimate Protect in the morning and a Crystal Retinal or Intelligent Retinol at night, and you have the complete framework.