One common myth surrounding SPF is that the higher it is, the less burnt you’ll get and the more protection your skin will have from the sun. In reality, the SPF number actually refers to the amount of time it will take the sun’s UV rays to penetrate the skin. For example, if you’re wearing 50 SPF sunscreen, it will take approximately 50 times longer before your skin starts to burn than if you were without any sunscreen.
Having said that, a higher SPF sunscreen can keep a small percentage extra of UVB rays out. This can make a difference, but perhaps one of the biggest mistakes people make is assuming that the high factor sunscreen lets them spend more time in direct sunlight without reapplication. This simply isn’t true, as the extra protection afforded isn’t so much that you can expect not to get burnt at all.