The American Academy of Dermatology says that one in five Americans will be diagnosed with skin cancer sometime in his or her lifetime, so wearing sunscreen is an imperative step when going outside. The AAD suggests choosing a sunscreen that is at least 30 SPF, has broad-spectrum protection against UVA and UVB rays and is water resistant. How much sunscreen do you need for a day at the beach? You need about the amount that would fit in a shot glass. Bottoms up!