What does “SPF” really mean?
SPF, or Sun Protection Factor, is a measurement of how well a sunscreen will protect skin from UVB rays, the kind of radiation that causes sunburn. If your skin would normally burn after 10 minutes in the sun, for example, wearing an SPF 15 sunscreen would theoretically allow you to stay in the sun for 150 minutes (10 x 15) without burning. This is a rough estimate, however, and your own skin, the type of activity you do in the sun (i.e. one involving water or sweat), and the intensity of sunlight may give you more or less safety. Note that SPF ratings can be confusing or misleading at times. For example, the rating tells you about UVB protection, but nothing about protection from also harmful UVA rays. The SPF scale is also not linear: SPF 50 does not prevent burns 2/3 times longer than a SPF 30, and in fact blocks only about 1.3% more UVB radiation than SPF 30. In addition, The Food and Drug Administration has expressed concerns that current testing methods may not be able to accurat
