To effectively block both UVA and UVB rays, the product you use must contain avobenzone, titanium dioxide or zinc oxide . Other active sunscreen agents, such as octyl methoxcinnamate, block only UVB rays and still leave you prone to damage from cancer-causing UVA rays. This is especially important if you're using AHAs, Retin-A, birth control pills, or other products that make your skin vulnerable to sun damage. Be sure to use sunscreen liberally. This means use a lot.
Studies show that most people apply only half the amount of sunscreen needed to be effective.
Cover all exposed skin with a generous, thick layer of product, and then massage it in. Reapply sunscreen every two hours when you're outdoors, even if it's cloudy. If you want a tanned look, use a self-tanner. They've come a long way since the orangey products of the 80s. Do regular skin self-exams to check for unusual spots or moles.