SPF stands for Sun Protection Factor, and the FDA defines it as “a measure of how much solar energy (UV radiation) is required to produce a sunburn on the skin.” The difference between SPF and sunscreen is that SPF is a measurement and sunscreen is a product — but they should always go hand in hand. Here's how to protect yourself from the sun.
John Hopkins Medicine recommends that you wear at least SPF 30 for everyday use, but it’s ideal to use a sunscreen with at least SPF 60. Broad-spectrum SPF means you’ll be protected from UVB and UVA rays, and make sure that you wear actual sunscreen under your makeup, since beauty products with SPF are not enough to protect your skin.
Also, putting on sunscreen once in the morning isn’t enough; you should reapply sunscreen every two hours. UVB rays are the main worry, since these rays are the ones that produce skin cancer. The FDA advises you to apply sunscreen at least 15 minutes before you go outside, so that the products will be most effective by the time you’re in the sun.