Vitamin C has a host of benefits, from protecting the skin from UV irradiation to supporting collagen production and promoting skin elasticity. Sunday Riley C.E.O. Rapid Flash Brightening Serum (£61) uses a powerful form of vitamin C called THD ascorbate to help improve skin's loss of firmness, the appearance of fine lines and wrinkles, dark spots, and more caused by time, stress, lifestyle, and pollution, all while rapidly brightening the skin's complexion.