Nothing weathers your skin more than the sun, says Sobel. Damaging rays speed up the aging process by slowing down collagen production and cell growth and forcing skin to lose its elasticity. Your best defense is a good sunscreen. Look for a moisturizer with an SPF of 15 or higher that provides broad-spectrum protection, meaning it blocks both UVA and UVB rays. Our pick: La Roche-Posay Anthelios SX Daily Moisturizer ($32, laroche-posay.us).