Pro-Collagen Synthesis Super Antioxidant Serum. Medik 8 C-Tetra is a revolutionary ultra-stable vitamin C serum which helps combat sun-induced damage to the skin, trigger collagen synthesis, increase the skin’s elasticity & density as well as improve the skin’s texture & brighten the complexion. Designed for both men & women in their mid-20s to 40s. Regular vitamin C is very unstable & many typical vitamin C products are inactive by the time they are used on the skin, in some cases, they have become pro-oxidant & actually generate free radicals! Ground-breaking stability data on C-Tetra guarantees real vitamin C activity & best of all, unlike L-ascorbic acid (regular vitamin C), C-Tetra will not exfoliate or irritate skin. C-Tetra contains 3% Tetrahexyldecyl Ascorbate, the most potent & highly stable derivative of vitamin C available. C-Tetra has been shown to have upto 4 times the potency L-ascorbic acid & other derivatives such as MAP (magnesium ascorbyl phosphate). Paraben & fragrance free.