Christina’s No. 1 summer musthave is, of course, sun protection. (If you don’t have a tinted moisturizer with SPF, you can try mixing your regular foundation with a dab of sunscreen.) She also advocates stowing away heavy powders and matte formulas that just sit on top of your skin. Instead, use sheer, tinted moisturizers, cream blushes and shadows, and gel-based lip colors for better staying power in the heat and humidity.