Skin cancer is the most preventable form of cancer, and using a high-quality broad-spectrum SPF is the key to that prevention. skincancer.org says:
"The SPF number tells you how long the sun’s UV radiation would take to redden your skin when using the product exactly as directed versus the amount of time without any sunscreen. So ideally, with SPF 30 it would take you 30 times longer to burn than if you weren’t wearing sunscreen.
An SPF 30 allows about 3 percent of UVB rays to hit your skin. An SPF of 50 allows about 2 percent of those rays through. That may seem like a small difference until you realize that the SPF 30 is allowing 50 percent more UV radiation onto your skin."
Because of this Megashdes uses SPF 50 for more coverage and protection from the harmful sun's rays.