What is the significance of the SPF number in sunscreen, and how does it relate to the sun protective factor of the sunscreen?

The SPF number in sunscreen indicates its level of protection against UVB rays, which cause sunburn. The higher the SPF number, the greater the protection. For example, SPF 30 blocks about 97 of UVB rays, while SPF 50 blocks about 98. This means that a higher SPF number offers more sun protection.