Sun Protection Factor (SPF): What do the numbers really mean?
Sun Protection Factor (SPF) doesn’t measure the degree of protection from UVB rays per se, but how long it will take for UVB rays to redden skin when using a sunscreen compared to the length of time it would take to redden without sunscreen. For example, if you use a sunscreen with SPF 30, it will take 30 times longer for your skin to redden than without sunscreen.
• As you can see from the chart, UVB protection does not increase proportionately
• An SPF 30 sunscreen protects against 93 percent of UVB rays only—not UVA rays.
• A sunscreen with a high SPF (UVB) rating—even as high as SPF 100—isn’t going to do the trick alone—you also need broad-screen protection.
